Repair Briefs - Guitar Amplifiers, Band/Stage Gear, A to E
The following are repair briefs for various
equipment.The infomation is directed
to technically competant repair engineers.Generic terms have
been used to make this info less model specific,eg terms like
replace transistor Q123 have not been used.
The equipment is Guitar Amplifiers, Audio Amplifers, Stage Gear.
I would be interested in finding
any other repair listings on the internet structured as i have
done ie intended to be less model specific. For convenience using search-engines,
use keyword divdevrep to target these files.
There is no point in contacting me about any of the following, the
repair job may have been done 15 years ago .
I cannot clarify or enlarge on any of the following.
In the following V ac means RMS DVM AC volts
unless stated pk-pk. Mains is 240V, UK
Should the location of this file change please use the keyword "divdev7" in
a search engine to find it again
A number of the pictures are now apparently not downloadable, because the hosts have disallowed
remote linking although not saying so. To view them , you have to remove the picture file name
from the picture URL and put this .htm file name in its place
and scroll down to the relevant pic.
Band Amps and other stage gear , A to L
AER Compact 60, made 2000
German made very expensive 60W "practise amp"
but well liked for its features.
The owner's cat , not a tomcat fortunately,
decided to piss on the cabinet.
Piss went down inside the Neutrik XLR/0.25 inch
socket and also corroded the gain pot so it
stiffened up too much to turn properly.
Easy enough to desolder the pot, clean and
ream out the aluminium corrosion.
The neutrik was a different matter,
could use the XLR input but not the 1/4 inch, horrible
blue-green mess of corrossion inside after
desoldering and prizing off the rear.
Cleaned out the worst with meths but could only
return to normal use by removing the grounding contact
that lodges in the rear closure, it would not cleanly
make or break and as had been used for months
without , in effect, the grounding due to corrosion.
As a pin for pin replacement not available in the UK.
pinning arangement (I've labelled the A,B,C as not on overlay)
A B C
2 3 1
B,C,1,R,SS,S were all grounded
with no plug 2 to ground
1/4 inch S=gnd, A=tip,R=ring
no plug R to gnd
Also fixed the rather crass foam cover in place with
strips of double-sided carpet tape.
Large Rs 2 x 82, 5W
TDA7294, 7815,7915, 2x 7805
33078 opamps, LF353
SSM2142, 470R, SSM2018,LM393,TL072
3x W24257aj-12, HC02A, HC123A,HCT05, AD SD 2115, CS4220
TL072,HCT14 and in all the amp just one
incidently "diode" DVM test readings for a good TDA7294V
relative to the heatsink
Akai AMX10 mixer amp, 1999
Dropped then nothing.
Surprisingly the latched connector between IEC socket and
ps had disconnected, large toroid filter broken away from pcb
barely held on by two wires and a crystal problem on the mixer board.
ps and amp uses K1181,2x K1179, .15,.22,47K,LT1509
6x 1k, 4x W38NB20, 47k,3x 1M
ribbon to mixer
AKG D1200E microphone
Broken wire inside
With 120R desoldered and no mike, inductor measured 98R/120R
Getting inside , unscrew meshed cover, pull out mike and desolder
marking which wire. Pull out the rubber grommet moulding, metal yoke
wires internal way round. With piece of dowel , no slipping, or
will break fine wire and push pcb out the socket end. After
removing socket screws but leave filter sw in place.
Used pan scourer as spittle trap instead of perished foam.
Alto maybe rebadged Behringer
Alto ACL2Pro near enough same as Behringer MDX2200 composer Pro
Alto L12 mixer, only 2007, not 2 years old
Intermittant loss of one channel , in different positions
of the master slider.
Undo handles and side plates. Remove the knobs
of pots and sliders only, not bush nuts.
Undo the 3 front and rear screws that hold top to bottom
of case. Break off, with pliers, the hot melt from the headers.
Undo the 14 screws from the top, not pcb
side of spacers, to remove the main pcb.
Beware the trick one under the graphic slider panel, threaded
stud so may undo. Remove the main pcb from
the panel at the end with the 2 small ribbon connects , first.
End-snipping and then grinding off the tinplate tangs before desoldering the
active pins is the way to deal with these tiny sliders , without colateral damage.
Getting inside, the non-resistive tracks are only 1mm wide and one pair of
single wiper "wires" must have been right on the edge of one such track so
intermittant contact, 1/2mm transverse bend and repaired.
Will resolder the remnant tinplate tangs for earthing and add hot-melt
around the housing where there is spaces.
4 tracks inside the 8mm width and 1mm for the conductive track and very easy for
the pair of wiper contacts can veer off track.
All 9 of these sliders are the same, but no problem with a channel one going
U/S unless someone uses all channels, problem was of course, Murphy's law,
on the critical one.
ps voltages printed on the overlay.
Ampeg BA115, 2008
sp 3.5R, mild ? PbF
NTC inrush 15R cold
No output from bad ground contact in phones so that takes the sp current
long pk for XLR
Ampeg BA600 - 115 bass amp combo, 6 months old, ROHS, 2010
D-class amps and SMPS
Yet another owner forgoing replacement/repair within warranty. I imagine the
importer has no replacements in stock as the whole batch has the same
faults. Perhaps bass guitarists should use pneumatics and proper compressors
to shift air.
Mechanical rattle noise due to brass cylinder spacers used over the control
pot bushes , loose bush nuts, so rattle.
But more importantly
At moderate levels an electronic crackle is the main problem. Remove the
screws in the cab to release the amp and one caged nut falls into the amp
space due to cracked cage. And a nut ( now known) falls out of its cage in
the screened off ps+pa section. The PA although supposedly 600W uses only
TO220 ,(4 x TOP66 in the smps).
Amp and its casing 6Kg but 22x21x16 inch cab and 15 inch sp only 18Kg so
maybe part of the problem.
TO220 in the PA is 3 on pcb , 3 on one section of heatsink and 4 on another,
no fans. As slab SMR nearby are 22R I assume for the moment the o/p devices
are powerFET. Each bank of TO220 held down by cross bar and 2 screws.
This is my scale of screwdriver torque
1 light finger pressure around handle
2 strong finger pressure
4 2 hands
6 impact driver
Testing the cross bar screws (they do have captive spring and plain washers)
torque measures about 2 , 1 and
then 1.5 and 0
The absent one either dropping out unseen as I knew a captive nut was loose
inside or still trapped under ps or pa.
So I assume silipads had compressed but these are 1.8mm thick porcelain,
even less compressible than mica. They were still in place surprisingle but
you could slide them with fingers and the TO220 nearest absent screw.
This is my educated guess as to what happened at manufacture as absent but
distinctive 20mm long bolt not found around here. The 4 output devices
should be held to the heatsink via a cross-bar over all 4 of them and 2
bolts thru it into the heatsink. The insulators are ceramic and the 2
central ones, butted up together , do not clear the retaining bolts on their
outer edges. After graunching the thread the assembler decided to leave it
out and trust to luck one off-centre bolt would hold.
Coming to reassembly I found a 3mm screw for replacement but it would not
hold, as tapped thread is stripped, so I tapped that one hole out to 4mm.
Tried grinding a clearance notch on the side of one pad but got nowhere as
Not only that but I had no trouble holding the slab in fingers while trying
to grind a slot , it was barely getting warm - good thermal insulator or
small grinding wheel not generating heat as not cutting into the material ?
As possibly BeO , should not have tried grinding into an edge
So ,lateral thinking, decided to grind down the screw thread where it
interferes with the ceramic , on one bolt.
I wonder if this was a one off at manufacture or a whole batch like this,
all that was needed was shift a tapped hole 1mm, plenty of room there for
that. Or one ceramic pad 1 or 2 mm narrower
Unfortunately it would not grind. I assume it was not heating up because the
grinding disc was just running over the surface without even rubbing , let
alone grinding, so no dust, still the flat edge . Does BeO have that sort of
translucent appearance of porcelain? I've managed to grind small sections of
the ceramic used is high temperature "chock block" connectors, that has a
normal solid white appearance. But given its use here then presumably BeO.
It was the slightly milky/translucent porcelain-like appearance that
I've seen pink TO3, presumably BeO, insulators before but they did not have
this transclucent like appearance.
I had to get inside that amp again, yet another PbF problem from next to
zero insertion force speaker connector at the PA 4 removal & inserts by me
was enough , only 6 months old.
The slabs pass red laser pointer light, but then on checking but so does the
ceramic of high temp "choc block".
These slabs are more trnasmissive and scatter the light throughout the slab
not just the entry and exit area of the chock block.
Complete scarttering with no obvious bright spot
directly opposite the entry point. Chock block ceramic was just the
adjascent bright spot , much attenuated in comparison to the porcelain or
vitrified BeO slab
These were not made for the job. They have a hole for either TO220 or TOP66
maybe size transistors . So too wide for this use and the hole is not used
. The layout does not mean they have to be 1.8mm thick , any thickness from
mica up could have been accommodated. Normally you would go for the thinnest
Cannot find that 20mm long screw lurking anywhere and extremely unlikely to
jump through the grommeted lead ports into other section of amp and then
fall out. Straight on , top and bottom x30 viewing of all TO220 soldering
looks ok, surprisingly. Did find some nasty rework/fudge. 2 standard radial
legged 10uF 50V, C19 and C54 soldered to standard SM pads, no thru board
holes. Near it a SM cap, C61 something like 100pF , had been soldered over
conformal coating with one end not soldered to trace, as coating under.
Owner has owned from new. 4x IRF450N power FET for 600W as D Class operation
As distortion was crackle rather than push-pull failure distortion hopefully
solder failure , think I can see ring cracks with x30 microscope at awkward
angle, pushing around the loose TO220 legs not obviously moving at solder
points) rather than some thermal runaway devices.
Drilled down deper and longer 3mm bolt for the missing one eventually.
Laid heat resistant glue over pairs of starwashered bolts and along the
cross-piece to definitely lock in place.
It does use 2x Int Rect IRS20955S, each one driving a pair of
there is an IR application note out there for those being used in Class D.
would explain the socking great inductor/choke well out of scale with all
the SM on that board. Will check that inductor is at the output and try and
locate a clock line , presumably back to the SMPS.
A generic problem with these will be mechanical noise from vibrating control
7 of the 9 were loose , in 6 months of non-commercial use. Not brass
cylinders over the bushes but are stop-ledged/ partial threaded leaving not
enough space for chassis thickness, nut and normal star washer so they used
thin plain washers. Luckily I have managed to fudge some thin star washers, too small inside diameter but I
belled out , using a tapered shaft nail punch to slide over and tube to push down on,
to go over the bushes - to remove would require inserting dart point and rotating off.
Downloaded the datasheet and that IRS is for pwm/D class operation. Input
,pin3, goes back via Q9 to 74C04 buffer so digital.
That large L , in a 53x53x24mm case is connected between the common points
of both FET pairs and across the speaker (with an ohm or so somewhere not
ascertained). That L1 measures 4K ohms , inductance not possible on LCR
meter as a yellow block HV polyprop? cap , label obscured by L1, is also
across it but measures 1.15uF apparently on LCR meter.
Speaker lead has a 4 pole connector for disassembly , 2 poles per wire, but
same size connector on the pcb only 1 pole each. Worse than that the commons
traces going to L1 are 3mm wide with solder run thickening for the current
but the 2 output traces going to the speaker are 1.5 mm wide and plain
tinned. So assuming 300 watt for a second into 4 ohm then about 9 amps.
From the Enumber in ul.com, it is 1 oz board and using
for 60 mil track and 9 amps for plain copper then 100 deg C rise , don't
know how much the tinning coat would change things , say an unlikely
doubling to 2 oz in effect, then 32 deg C rise , unacceptable ?
Can you have the bridge of a bridge tied D-Class filter of form
as single L and speaker and C in parallel
L is inductor ,Sp speaker,C capacitor
I'd forgotten the double wound toroid inductor of 360uH in series either
side of the speaker.
What sort of value of inducance for L1 and its wire gauge/current carrying
requirement for 300 to 600W use? C 1uF, 250V
I removed the filter cap to measure the inductance of L1 . Cap marked 1uF,
This L1 weighs about 170 gm, estimating weight of remainder components and
pcb from total of 290 gm.
Through a hole I can see some wire about 1mm diameter.
Using 1KHz RLC meter, L1 measures -2.2H on H scales and -140mH on mH scales,
don't know what that means , will try and find a manual for an Avo B183.
Maybe faulty, but measuring plain inductors through the scales is positive
and consistent across neighbouring scales.
1KHz ac resistance is 230R, DC resistance is 4K so perhaps what is labelled
as L1 is R and L in series.
Perhaps R of 4K and L of .6H , to give 230R at 1KHz, but if wholly 1mm wire
I cannot see how 600mH with 170gm of 1mm wire, strange core material?
I could not find a manual for the B183 or B184 . I tried an audio output
transfrmer and a resistor but no negative readings on the meter. Perhaps
there is another capacitor inside the can , other than this external 1uF
that I removed temporarily.
It almost seems perverse, 0.4 amps of mains current draw (at 240V) and 25
watts of 400Hz sine into 4R dummy load and a thermometer laid over the tabs
of the 4x TO220 output device, rises only 8 deg C over ambient.
And that with amp laying on bench so no convection over the external
heatsink vanes, no wonder no fan needed.
Previous D class I've played with were Stagepas , not possible to monitor
their operation without making up umbilicals to operate PA out of the little
box. And as separate clock maybe "RF" problems doing that
Do Ampeg make bass amps? There will be loads of returns of this model.
Any large lump inside a bass amp is likely to vibrate if inadequately
secured. That 2 x 2 x 1 inch lump is only secured by its screening can at 2
pointsplus inductor ends soldered. That was the main problem , proper solder
would be hard pushed but PbF only lasts 6 months like this.
Also PbF failing on the speaker socket, would not have been so bad if they'd
used the 4 pole connection like farther down the speaker line and bad PbF on V2 of prea. Plus the
absence of star washers on the pots. Ignoring the absent h/s bolt.
PCB construction of the PREA pcb ,
where holes are drilled for thru-board components but of diameter far too
big , thru-hole plated , but no eyelet/inserts used to fill the gap. So
1N4001 size leads in holes twice their diameter and 1N4148 in holes twice
their diameter. So not a case of only one drill size for all. So in area
terms about 1 to 4 ratio of lead to solder. Bad enough practise with proper
solder but with PbF, ring cracks starting all over.
Is it to avoid mutiny by the by-hand board populators ? Loads of suspect looking
possible PbF ring cracks on th ePREA
To get the amp out of the cab. 3 screws each side. Thin steel rulers either
side to release amp from cab. While at it open out the 2x pairs of holes in the cab
, drilling through the wood, to make alignment of screws easier.
To release PA+PS cover 2 rows of smallest screws and 2 countersink at either
end. Broken caged nut, small size cages. Found replacement 4mm caged nut but
too large for the existing holes. Ground back one arm only of the spring clip
to get into the square hole, the other into gap between cover sections and stopped
it shifting out of that gap with hot melt glue in there. Replacing amp in cab hang top 2
bolts first, rear flush with cab sides and heatsink recessed about 2 or 3mm inside cab line.
and lies with about half inch gap under to the cab ledge. 2 sheets of celluloid
at the bottom helps reassembly
Mains filter section TH1 cold 8.2R. R66 and R72 measured 330K, markings 750K ?
PREA 820R, 10K, 4x 10R , 2x 100K?/R? large Rs
PS 10,1L,3x10R ?, 47K,22R,2x 68K
PA empty pad has no chassis pillar under
Maybe ringcracks on 2x TO220, under x30 mag.
Speaker 3.7R, consistent at all times so hopefully PbF in there not playing up.
Power level control/crossover each lamp 1.3R and inductor about .2R
PA 7915, 7815, 7812A
TIP32C, TIP31C LM35DT temp monitor, 4x IRF540N
74HC04, 082, 72, 293M, 4580M, 339M
VTL5C7 opto coupler
U21 E78E 805J89
C19 , C54 10uF, 50V soldered to SM pads
Black sc 5 short and 1 long (to SMPS Tx cover ), 2 medium length for SMPS Al angle plate.
C61 soldered thriough conformal, one lead to o/p FET common, S of one D of other.
Other lead to 10uF (CBS) to pin 15 of IRS..
R25, R26 01C = 10R, C1D = 8.84K
In cct with RLC meter ,measured 1.43nF over C83
and with C61 replaced with 120pF measured 1.53nF so perhaps C61/C83 is about 47pF.
I managed to overcook the original on removing and did not fancy removing the other
one just to measure out of cct.
Full mains ps V at sockets
pa W -44V, Y -25, Bk 0, Be -44, R 44V
prea R -15.2, Bk 0, Be -15.3, Bn 13.8, Y 302V
prea to o/p 0,-15,15,0,0,0
0, .4V, 0,0,0,0,0
4R dummy load, note not ground referenced
400 Hz output 10V ac over 4R for 46mV in with all controls at mid
and vintage ch. About 0.4 amps mains draw and only 8 deg C over ambient for
thermometer laid over tabs of op TO220 considering amp laying horizonttal with h/s under
Access to speaker wiring removing RH side (from front) hives horn access as well.
Dart point in corner and lever will remove front grill panel off the
velcro pads, leave labels in place.
Rustle noise above a certain level and then continues on reducing volume, feeding in 50HZ.
When good 3V across speaker but with rustle 2.9V say.
R-C across speaker brown polyester cap and 2x 22R 1W sM in parallel for R
Bad solder joint at pa speaker connector (2 pole only) and trace on upper side
of board , lever up shroud enough to introduce solder while heating from below.
Bad solder at L1 to traces, while resoldering fill in the missing solder thicknessing over the
traces near the ends. To brace this large L1 decided on a solder tag introduced between PS
Al angle and chassis using existing bolt through. Length of pen barrel with hotmelt in either end , one
end slotted to go over solder tag. Other end build up with hotmelt into hole in L1 casing,
hoping reduced ventillation? not significant.
With 4 wire prea-pa lead missing, very little hiss from speaker.
Still rustle noise above a certain level. Turned attention to prea. Amp would work fine
laying horizontal , put back in cab and play up.
Probably bad PbF at V2 socket as that area sensitive to twizzling , fine with 12AX7 vertical but not horizontal.
Replacing V2 made no diff. Remember double
sides so solder points both sides. Opto coupler soldering looked bad
also . Redid all large R and C on both sides.
Ampeg B1, 1992
Blown transformer due to shorted op device and TIP device
broken pull switch spindles repaired as PTF.
2x MJ15001, 2x MJ15002, TIP31C, TIP32C, 2N3402, 2N3440
220R, 10R, 3.3R
2x 10R, 100R,
2x 1K, 4x 0.33R
N/C th sw
Arion (Prince Tsushinkogyo) guitar tuner,1985
Not chromatic (new one on me) ie not full spectrum ,
does not have pitches "C" and "F" , dedicated to guitar use.
Bad on/off, probably lead/jack trodden on and broken solder
on socket joints, no nut mechanical holding of the bushes
Ashdown maybe worth checking Trace Elliot, Orange or Peavey as related companies
Ashdown ABM500 bass amp, 1997
Had been seriously dropped in a flight case and a number of problems, now
sorted so it now works but there is a fairly low level background hum
problem with no input. Attending to all the pots as most were
worn or suspect in some way and some solderings at the heatsink.
Festoon bulb replaced with a physically larger
12 V bulb so mount needed extra fixing in place,
o/c voltage supply, has dropper, at the bulb mount 17V ac.
Some other data secondaries 13.5V; 62,0,62 ;
17,0,17 ; 270V (16 ohm DC )
main ps , +/- 84V
Thermal sw n/c. 1V dc over meter reads "2".
At 22 deg C , the heatsink thermistor , in circuit, measured
70 ohms giving only 9.6V at the fans, parallel with 68R gave 11V and 28R // gave 12.3V.
To remove the preamp board, remove pot and switch knobs
and push in switches and slacken off the transformer to give space.
Shift the other way to remove the rear board.
See tips files for coachbolt removal problem.
All inputs and outputs and pots (exept the pot casing) are electrically
isolated from chassis, on schema and in reality.
Just the mains inlet earth bond point to the chassis.
The pa has a nominal "grounding" point of // 100nF + 10K, 1/3W R
and the pre has the same to chassis and the signal line "ground" between
Another sort of problem with this faux ground arangement.
I thought it odd how long it took to drain the 450V caps and the main
reservoir caps, before I previously dismantled all the boards.
You have to connect the low ohm resistor to faux ground rather than through
20 say + 10k//10K to real ground.
So about 5K between real ground and nominal ground.
Disconnecting the signal lead, the pa o/p is clean.
Driving into 8 ohms , with shorted inputs then at max volume setting then
0.7V on DVM ac range, dropping to 0.002 V for min vol.
It is more intrusive than I would normally expect but I don't have any
figures for what is normal.
shorting the preamp 10K then the hum goes.
The input 1/4 ins shorting contacts, with no input jack, are ok
Putting 1K across the pre amp 10K then the hum level drops to a much more
acceptable 0.1V. What are the safety issues with this sort of arrangement ?
They are not marked on the schema as
fuseable resitors nor on board marked ! in a triangle.
I've probably found the source of generic hum noise problems in Ashdown amps
with this faux ground structure.
The problem pot marked with a "B" meant it was linear and not log so a
replacement easily found.
Taking the original apart there was no broken track or rivet /paxolin
failure, stressing/bending paxolin and measuring etc showed nothing
But I did notice the track was offset, ie not coaxial to the paxolin base.
The noise intrusion was most prominent at about 2/3 and at that point due to
the off centre track and slight ovalling of the outer pot casing the
track/wiper at this point was very close to the casing.
For the replacement pot I bent back the four tangs that hold the middle
casing/housing section of the pot to the bushing plate, introduced four bits
of insulation, closed back on them and glued in place.
So the casing is now isolated from the spindle and bush which is still
properly grounded to the chassis.
Now normal hum level with shorted input and maximum vol/gain settings
varying from .04V clean to 0.07V ac on full grind setting
into 8 ohms. So factor of 10
or better improvement just from isolating that one pot casing and presumably
more centrally aligned pot tracks perhaps to lesser effect.
The 2 x 10K faux to ground resistors still as the original design.
One of those annoying self-made, in a sense, problems also associated with
the faux earth.
Trying the amp with the equalisation board free of the chassis was fine but
mount it back in and horrible mains noises.
To save messing about I was temprarily placing the board back in without the
3 spacers on the 3 pots. These pots have the casing to chassis earth but the
4 slider pots have the cases connected to faux earth. Without the spacers
then the slider cases came too close to the chassis.
The grid vltage on the ECC83 varies from 0 to -3.8V via
the clean/grind pot
I wish there was a proper techie/muso translator somewhere ,ie full
translator techie-speak for techies and muso-speak for musos . What is grind
? in terms you can see on an oscilloscope for instance, not the usual muso
I want to know, in this instance, if you feed say a triangle wave in what
comes out on full grind?
Final loading check , 400Hz, giving 20W
in 4 ohms, no rise or drop in Vac over test period.
Heatsink with the 2 fans active gave
20 deg C rise over ambient of 22 in 12 minutes.
Also into 4 ohms, no input , clean channel
full vol & gain of 0.03V ac of mains hum over the load
Ashdown ABM-500 EVO-II Head, 2002
Intermittant crackles and gain dropping, part into a set
with normal usage.
2 temp sensing things , one vaguely touching , the other bent away from the
Perhaps every roadie should be put in a flight case and dropped down some
stairs as a lesson.
Anyway both heatsinks must have bent relative to the pa pcb, bending the
leads , when dropped. Main spring held items stayed ok.
How to anchor back more firmly than just white paste? The main TOP66 power
devices etc have those slide on spring steel clips but the loosened TO92
tranny and fan thermistor are a long way down from the mounting slots, for
anything like that. Any ideas ? - live heatsink btw, hence not rigidly held
Too crowded to drill/tap the heatsinks and the assembly of
these sort of hook-clip arrangements is realy make once,
dissamble/reassemble at your peril.
This is a likely generic fault scenario for all
such "live heatsink" amps that are only fixed to flexible polyester pcb
Double sided foam/tape tape was supposed to be keeping a duaghter board
marked EB SUB ? (4013 and 3 x 072) fixed
to the preamp but dislodged in the same drop presumably, failed solder
joint/s leading to crackles.
I removed 2 nearby caps , 2 small holes ,to match cap pin spacing, in cut
down lengths of cable-tie , and soldered back in, regooing and positioning
the 2 shiftees. Volume was fading down after half hour of use, presumably
because the NTC fan thermistor was staying at room temp and fan speed not
upping with increasing heatsink temp.
Unsupported daughterboard is now braced back to 2 chassis anchors
NTC thermistor TH1 ,88 ohm cold
2.2K,4.7K, 1W, 4R7 vitreous
33R , 1W on prea board
main bridge rect , one prong poor solder, supply pcb conn block
for fan , bad solder.
Returned for "repair" years later , dead at power up, repeated pressing of
"Mute" made no diff. As received , no proiblem, added 2x silicone sleeve plus2x Hamma beads
to the Return Tip bypass sw as
the compact type and next to impossible to clean. Made a slot hole in the pcb between the
Send and Ret so, and wired across to replace the cut trace.
Returned some years later. Failed , no output, after using in/out leads at the rear.
As compact , tight footprint , and difficult to clean sockets. To avoid blanking off and making a new chassis hole.
Drilled through pcb at the common trace , so wired in a replacement. Then doubled
up silicone sleeving and Hamma beads to reinforce the sw action
Ashdown Acoustic Radiator 2, amp, 1999
It was only when I saw the IEC on the rear that I realised it was not 1960s,
scuffed red mock leather covering, large thick leather handle, "ivory" knobs
, that cream stove enamel used on a lot of medical kit etc of the era after
the crackle finish of the 40s/50s.
Now I've seen it all. To get the amp out you need to remove a speaker to
release the speaker wires internally. But its a dummy speaker, presumably
the 2 in the model name means 2 speakers. Basket , suspension , kevlar
looking skirt, and cone , only. No pig tails or holes for pigtails or Voice
coil or magnet. So if these were off a production line, how were they
further processed? 4x3 sets of holes in the basket for what I would have
thought were screw holes for a magnet , but sealed off by the seated cone.
Would they glue in VC to the cone and magnet glued in to the basket with
some sort of active monitoring of sound output , while posistioning in the
Problem is the otherwise Ashdown Bass amp common symptom of loss of output ,
returning a few minutes later, but this one will then continue for an hour
or more with no drop-out. Not had a chance to power up yet , to investigate
Never seen dummy one before . I've seen holes in boxes called adiabatic resonators , yes,
so I'd believe anything was possible.
What is an active loudspeaker , if not an acoustic radiator? The company
blurb refers to 2 speakers which to my mind implies 2 of the same sort of
speaker . Eiter 2x active speakers or 2x passive speakers which would likely
result in a lot of returns
Tweeter 4.1R, bass 4.9R
2x lm3886t (slide the spring H/S clips)
Remove front expanded Al sheet and reset the dents and restress with weights and add hotmelt glue
runs against the frameing
Brass sc to retain the amp
RH sp is dummXover wires are close to shorting
cut sp wires and add terminal block
open up hole in the wood for sp wires
Active sp marked cone
20 2015 D9 1?99.78
and barcode on magnet
added tap washer under the bare sc only just holding the handle to the cab, as original broken
Jack in tuner F/S will kill the amp, or into S or R will seriously attenuate the amp.
Setting I was in , pulling the vale made no vol diff
bad low i/p so, scratchy Tube pot.
Lot of bent pot shafts
Whole board under the digital pcb loose from the chassis , all nuts in place just
Chassis rear is meant to have those wonky angles.
Q pot pulled out and bent
Discharge the 450V caps , 250V on one 2 days after no mains
Discharge at R31 and 38
solder ring crack at .25" so tip
Made replacement stem for the unobtanium quad pot
Taiwan alpha B 100Kx4
1.5mm thick Cu strip 45mm long and ground down to 3mm wide
at interior end, protrusion knotched to take dollop of hot melt
mid pot posistion, outer pair measuring 48K , inner pair 21K.
Cu strip should have been 1.9mm for a tight fit
rear level pot loose
some 1/4 in so bad solder
all sc terminals for power could be tightened
replaced the XLR
292V and 276V on 400R and .7amp mains current at 240V and
V1 glowing dull red
-13V on R63 bias
Tank 57R in , 210R out steel grounded on o/p side
Background hum increases with reverb pot
from amp short lead has ground shield wire to R25
RMS noise .4V ac with R6 , no i/p , over 8R / .024V ac in the correct way round .
Long lead to Tx end
Replace meter, then graphic panel with lamp at meter, then main board .
With less than 80% mains then a Jacob's ladder buzz
Something bad about lowZ Z socket, middle contact required to gnd with a mono jack.
With stereo jack low level o/p with tip and sleeve, needs the R-S connection for
full o/p. So 2 chances for 2 contact failures , although no bypass contacts used.
75mV of hum when amp is placed inside the cab, added mu-metal
draped around the Tx, reduced hum to 50mV (25mV when out of cab)
2x 150, 2W
2x 4.7 , 1W discoloured to white blue gold , 2.7R on overlay
Ashdown Electric Blue 180, MAG250, 2004
IEC inlet broken and fallen inside along with the line socket.
Replacement IEC plus fuse needed 2 screw holes ball-milled into the steel .
Discharge the H/S s before undoing PA pcb screws
usual suspects under and lacquer on the sc
Ashdown Electric Blue 180, made 2004, 26Kg
The amp cut out totally and when it had cooled down
and he switched it on , it worked, but he
noticed the fan was not turning so he
switched it off again.
Beware the heatsinks are not grounded
and +61V on one and -61V on the other.
The supply to the 12V fan is off the preamp board
so had to remove from the front pannel.
The owner had never had to tighten any knobs
but one grub screw (brass) had been graunched
at manufacture so had to drill that out
first (see the tips files for technique).
The 100 ohm dropper to the fan had resonated
and failed inside the pcb hole, copper coloured
fracture face so presumably work hardened copper
failure. 150 ohm dropper in the display area had
overheated to 156 ohm and giving apparent band colours of brown
Uses 2SA1668 , 2SC4382
2068, LB1443, 5x TL072, M51134FP
2x .33, 4.7, 4.7K large Rs
Speaker DC resistance 5.6R
Ashdown Mag 200
Bad intermittant throughput, but not wh me, of course, all good.
Bus as bad in either input, probably bad EQ SW and also changed
axial type RETURN so. to conventional.
After replacing the EQ sw with a standard toggle sw and wiring into place, (opened out star circlip to seat centrally in the too large
panel hole), turned out was due to bad solder at a cap connected to the sw , close to the sw.
Then further problem of no output, due to bad solder on sp
output socket, both were bad
Ashdown Mag 200, 2001
Bad no-name input 1/4 in so, or pehaps bad solder pad. Cross-coupling meant problem
on one would affect both inputs. As a pot shaft was bent , perhaps the cab had taken a bash.
Tip contacts bent or misplaced.
Replace 2x 1-K with longer leads so can bend out of the way of replacement
conventional wired in replacement so.
Effects return so is switched but its gnd solder point was bad.
Tx 1-.5R// E 2.5R, O 2.6R
Remove 2 front caged nuts before removing the Prea pcb
2x 56R resoldered as heat browning
Remove the copious dollops of white goo
Tape over the input socket ends , while some hotmelt is molten between them and the pcb
while placing in the chassis. When cold, demount and add more hotmelt around the pins.
Wiring to one so, around pcb edge and a hole made in the pcb for the other so wires.
Ashdown MAG 200, maybe 2000 or 2002
Combo with 1 x 15 inch speaker.
After hour of use it cut out.
Next time it failed after 10 minutes.
Lead-free solder "volcanoes" or electrolyte
from the 10uF cap near the J112A N-D type FET
caused solder failure on the cap and falsely
triggering the protection circuit.
In use voltages on the 112A were 0.2,0,-8V
clicks over at about -1V
As mosfet, discharge the reservoir caps before
dismantling if no speaker load. In working order the Source to
ground of each power fet shows a forward "Vbe"
one way or the other and only that terminal.
To get to the front board leave the 4 nuts in place
and remover the 2 captive nuts and the
2 small screws on the top. To replace
put the sleeves into the front panel
rather than on the pot shafts and locate the
meter into recess before pushing in the
pots and switches and sockets.
The thermal switch T'-key 125-a15 code
meaning 125 degree C, I took to 120 C
and did not change state and not mechanically
Also 3 of the pots were (needlessly) long
shaft with nothing other than paxolin and
nylon bearer around shaft keeping them in place.
Could easily have used the normal shaft ones
and extend the pins, so proper bush nuts to
front panel could be used. Replaced with a
panel mounted one , wired into the board.
Meter had been pressed in and soon
would have had solder joint broken.
Made a hole through the pcb for a nylon bolt and
nut glued to the component side of the board so
could be tightened against the meter when aligned
and fixed in the chassis.
I do not know if this is correct setting but this VU meter
was 0 on scale with 0.18V RMS 1KHz input from a 600 ohm
source and input pot at maximum.
I don't know what the illuminated meter looked like as original but I reckon
my re-jig would be better, looks quite nifty,
although not 'retro'.
Because the cover protrudes 1mm or so it even looks effective
when viewing skew-on.
Put a 2K , 3W dropper in and a bright blue LED wired-in and moved to
vertically under the meter movement when mounted in chassis and
angled toward the ring section, so internal refraction ,
through the plastic, forms a blue ring around the ali cut out , especially
after abraiding the coating off the aluminium in that recess, plus a bright spot under the
meter that shows in bright ambient light and it also throws a light on the
scale. Filed a small notch angled downward so the
front periphery to the meter was still circular but
allowed more light into the bottom area of meter cover,
revealing more of the LED directly as an indicator
for bright light conditions.
2 LEDs , under but angled in and across, would have been better as the static part of the movement
shadows part of the light cast.
Comment on return to the owner.
"looks amazing! thanks for doing that, it really makes it stand out, cheers"
The 20mm fuse on the preamp board is too close
to the metal edge so covered with a cut-down piece
of wide flatted-U file binding spine.
As all lead-free solder redid all
heatsinking joints on both boards.Main AC rails 50-0-50 and
Ashdown MAG 300 amp, 2004
meter movement but no output, no hiss
Both 6.3amp fuses blown, 2 diodes of the bridge rectifier s/c. Internal failure of this bridge, dodgey looking splodge logo, presumably Fronter logo and 8amp rating, marked
or something else to change as well?
Main caps look ok and ESR (for what its worth in such cases) ok
The 2 failed diodes are
-ve to AC
+ve to other AC
Suspiciously 2 solder points look like crazed PbF solder but all is SnPb,
melted and reformed? the 2 points are at the -ve terminal and the AC terminal of the other failed diode. Output devices DVM-D cold test as expected. No heated traces or even obvious gaseous eruptions from the bridge or anything out of the normal. No reported preceeding noises prior to failure.
Looking at the Frontier datasheet, the bridge has to be derated to only 3 amps at 40 deg C, which seems surprisingly low temp. This amp was all day sitting outdoors in the cloudless sun and failed after 1 hour of use in a set. So 40 deg C was quite likely exceeded, so probably the reason for failure.
As constricted in space , without going off board, I see a heatsink being bolted to the replacement same rating bridge, or wiring off board and bolting to the chassis
I cannot see how an honest rated 8amp bridge could be in a 15mm square pack. Replacement will be 4 amp 200V rating, with a hole to take a vaned heatsink, no hole in the original (perhaps to get 8A it uses the central area). The fan airflow in these amps is fine for the output heatsink but the bridge is sheltered by the main caps and wiring knot, vane will be off-centre poking into clear air, off the edge of the board
I picked up the wrong bridge, the original Frontier one does have a central hole
with 4x10" cab, combined sp imp 5.1R
no fixed DVM-R or D at sp outlet
8AC6 = 35430DEC
tighten and lacquer sc under h/s. Tied the vaned h/s bolted to the bridge, to chassis base
-70V on outerh/s , +70V on inner one
returned to owner and bounced back
-25V on outer H/S, 0V on + h/s
Both fuses blown softly , after 1.5 hours of use and volume turned up.
With catastrophic failures I initiaaly down rate fuses , in this case to 3.15 amp but forgot to
replace them with 5 or 6 amp ones
PA overlay marked
EB150 , T5A 36V
MAG250 , T5A, 45V
presumably AC, as MAG300 is higher V then assumed 5 amp were correct value instead of th initial
6 amp. If 2x 5A blow then 6 amp ones wil lgo in there
(NOTE to myself , next time some bright silicone rubber rings placed around such testing purpase down rated fuses, next
Noticed C15 and main cap C16 both had marks from abrasion or perhaps discharge.
REmoved C15 and added extender and reorientate , on end, to clear the main cap.
Sp leads have anti-shake spades , push to release
Ashdown MAG 250
For factory retro-fitted fans.
4 faults in one just fitting a fan and power bleedoff
For random fan stoppage - look for
Instead of 47R 5W W/W placed in line with the fan (dangling R unsupported at
one end) , 0.047R soldered-in so 21V across the 12V fan. Surprisingly
thousands of hours of unproblematic use like that.
Even without that , for any long term excessive wear on the bearing of fan ,
the reaction force pushes the impeller towards the mounting bracket,
eventually touching it. You could see a slight trace of where one fan vane
had rubbed the bracket and rubbed the plastic of that vane, ie clear of
usual gunge. If meter cover stays in fascia cover to protect
when working on prea.
Replace with 47R, supported by tagstrip bolted to fan, and new fan with the centre section of the
mounting bracket hacksawed out. Take negative lead via a wire
to an added terminal set in the prea.
Fourth mistake : the fan just circulates the air internally, no added
baffles to duct air in from outside. Set the fan in a stiffened
card bafle going from LH corner of front to
centre divider of rear vent.
So air heats up, softens fan's plastic vanes , vanes flex a bit, to the
extent of touching the mount.
Removed the the sw and checked for temp action and
any vibration sensitivity and checked caps in the controller area.
If the sw goes o/c in these Ashdowns the gain
drops at the top end mainly, not cut out .
1KHz in and 1V ac over dummy load then if sw changes
then o/p drops to 0.04V ac, less so for lower frequencies
which seems upside down for amp protection.
Still random intermittant gain drop and distortion.
Beefed up return socket switch as per tips. The holes and pads for these are far too
big for the pins so a good place to see crcked solder, but not this one, so far.
R46 , 1/3W, resitor at the 1.6K bias R cold joint.
Ashdown MAG 300 amp, 2004
Both 6.3amp fuses blown, 2 diodes of the bridge rectifier s/c. Internal failure of this bridge, dodgey looking splodge logo, presumably Fronter logo and 8amp rating, marked
or something else to change as well?
Main caps look ok and ESR (for what its worth in such cases) ok
The 2 failed diodes are
-ve to AC
+ve to other AC
Suspiciously 2 solder points look like crazed PbF solder but all is SnPb,
melted and reformed? the 2 points are at the -ve terminal and the AC terminal of the other failed diode. Output devices DVM-D cold test as expected. No heated traces or even obvious gaseous eruptions from the bridge or anything out of the normal. No reported preceeding noises prior to failure.
Looking at the Frontier datasheet, the bridge has to be derated to only 3 amps at 40 deg C, which seems surprisingly low temp. This amp was all day sitting outdoors in the cloudless sun and failed after 1 hour of use in a set. So 40 deg C was quite likely exceeded, so probably the reason for failure.
As constricted in space , without going off board, I see a heatsink being bolted to the replacement same rating bridge, or wiring off board and bolting to the chassis
I cannot see how an honest rated 8amp bridge could be in a 15mm square pack. Replacement will be 4 amp 200V rating, with a hole to take a vaned heatsink, no hole in the original (perhaps to get 8A it uses the central area). The fan airflow in these amps is fine for the output heatsink but the bridge is sheltered by the main caps and wiring knot, vane will be off-centre poking into clear air, off the edge of the board
I picked up the wrong bridge, the original Frontier one does have a central hole
Ashdown MAG 300 , EVO 2, 2008?
intermittant cutting out, banging the cab will reset for a while.
pa +/-71V on the heatsinks + one nearest Tx . Discharge the main caps before dismantling, regardless of whether last used with
speakers or not. Top thermal sw n/c
There is a bang preceeding siilence and another before returning to normal.
Stick pierced cloth tape over the caged nuts to avouid tearing up the lining shield foil. Beware
of pushing the meter front when replacing amp into the cab.
The sp cable is squashed to accommodate sliding into the cab.
ring cracks starting at sp outlet.
inadequately tight 8sc on PA pcb , added lacquer.
Bad plating? on Harwin connector pins , 100 percent tin plating tinpest problem?
Because of the sharp edges to the tops of the pins I would haveexpected any pbroblems
with the plating to be on the socket pins put plating there is fine as is the crimps
Added RTV to major PA components as can rock easily
Resoldered C5, C8,C1 on PA in case of false protect mode
Ashdown MAG 300, 2004
pcb marked MAG250 EB150
Blows mains fuses during low volume practise session.
Survives long enough for the meter lamp to come on half
a second. Nothing found obviously suspect in ps or pa probing around cold
and inspection. Bad internal AC
supply fuse holder contacts , arcing burn marks on the fuse barrels. Both
are 5 amp rating but neither blown or showing stress on the fusewire.
So much for so called "Top Cheers" transformers.
Initially could take variac to 50V and then run away , now cannot even put
the minimum of 5V on the primary , with nothing connected to the
So just coincidence of bad fuse holders on the 48V ac lines or directly
leading to failure ? Could repeated breaking of secondary current induce
very high voltage in the primary leading to shorted turns?
Nothing visibly wrong through the tape wrap or smoke trails from inside. DC
measurement on primary now about 1 ohm , unpowered, was about
6 ohm when received.
The first winding was the low current 15-0-15V secondary. This was wound
with doubled up .45mm wire in one go so reducing the number of shuttle
passes to wind on. The 2 wires brought together to form the "0". Thought to
myself, perhaps that is ok for low voltage winding as only 50V peak or so
maximum for 2 thicknesses of lacquer to sustain.
Then the 3 amp 48-0-48 wound as 2 separate layers of 1.06mm wire, not run as
paired winding, fair enough. Anyone know why 3 runs of loosely packed turns
per layer when one run of tighter turns per layer could have been done, so
Get down to the unruptured thermal fuse, tails of the primary and the .7mm
wire primary and nothing obviously wrong in the way of hot spots. But
blow-me-down a return to the paired up winding and ends joined to give
120-0-120V for 240 UK use. But of course now 2 thicknesses of lacquer having
to sustain a normal maximum differential of about 350 volts.
Totally wound off and the small burn patch was midway , where
maximum voltage difference is/was, so just required some otherwise
rather minor, short duration, mains voltage spike to
Thermal fuse marked Klixon ?
From http://www.sensata.com/download/17am.pdf not fuse but bimetal dome switching on
combined temp and amperage maximum 8 amp , take the 3 digit number ,
if starting 0, subtract 7 and multiply by 5 so 033 == 130 deg C for sw temp.
If number >060 subtract 40 first, if >160 subtract 140 first, if >200 subtract 180 first
Difference on cold probing between drivers on both
sides of the amp due to resistance 47 + 330R between B-E of C4387/ A1668
but not corresponding ones.
If gingerly powering up this sort of amp don't
have a speaker connected as amp is unbalanced below about +/-25V.
Powering up on bench power supply and monitoring output line
+/- 10V o/p 9.9V
+/-15 o/p 12V
+/-20V o/p 18V
+/-25V o/p settles at 0V
Uses +/-70V 2x 2SA1294 , 2SC3263
Output pot goes past the endstops, dismantled and
reformed the outer case. Meter on this ashdown
stuck at the top, needed desoldering off the pcb,
measured 650R and read 80 percent on DVM voltage,
unstick the tape before resoldering.
Ashdown Mag 300 No output after someone replacing the fan and
not discharging the main power rails at the o/p device heatsinks.
Touched one of the fins to the prea -ve power rail.
Shorted the -15V zener and at least one of the 072
IC2 / IC3 . As received static 0.43V over the meter . Replaced the zener
but problem with the bass pot so that above 1/2 then
distortion and then cut off.
-11V on pins of the ICs that should be about 0V and
varying DC on the tone pots.
Ashdown Peacemaker 20, 2003
Loss of preamp, pa ok with external feed
0.05V 400Hz ac into return produced 3V ac over 8R , "maximum " volume set.
Signal injecting at pin 6 of IC2 and IC3 produced o/p
10K dropper failed in valve anode supplies. No obvious
reason for failure , even breaking open, no overheating
or colour change to body or bands . Replaced
R11 and R23 also
o/p tx 0.9R
R90 22K replaced with 2x 47K , 10K in the schematic and A1=A2?
To refit main board , and 1/4 socket spacers, 3 each to the front and
2 each to the rear
Ashdown Peacemaker P60 valve combo, 2003
Volume fluctuation and background rustle
I discovered how to get into it, remove front knobs etc and remove the facia
panel first. Lever out the mains switch enough to
pull the fascia around it.
Remove and replace amp with cab on its side.
Meter unslots and tape it to the underside of the chassis.
This amp runs very hot in the region of the EL34 output valves, almost to
the point of charring the pcb, localised black rather than just brown
discolouration, through the bulk. The valves are inverted and no ventillation path
under or around the valve bases. There is plenty of space to mill holes in
the pcb around the periphery, and avoiding traces, to allow some ventilltion
Scraping back some of the pcb surface browning and into the bulk of the pcb
material , the browning extends the depth of the material. Also some brown
staining on the surface of nearby solder points, probably some vapour coming
off the polyester and settling on the solder. No ventillation grill in the
cabinet top either.
I'd half considered a fan but there is no obvious place to put it and
without cutting a hole in the steel chassis or the wood cabinet it would
just be circulating the air, unless mounted outside the chassis , directed
over the bottles. Could use the rectified heater supply as a less than 12V supply
for a fan.
Cut a 3 x 2 inch hole in the cab top , masked with grill.
Positioning it asymmetrically off-centre in both senses so above the big
bottles and clear of internal encumberances so a 2 inch fan could be fixed
under the grill , later, if required. Bolted down some metal bar etc
with the handle bolts to form a slideway, for 45 degree drill bit
guide to slide and step along to cut 2 angled slots to bring
the vent hole inside the chassis. Cut through the ends and tidied up
and painted black.
And the pcb perforations with dremmel and 1/8 inch ball mill
Putting a thermometer in the quiescent vent flow, 40 degrees C above ambient,
better out than in.
On EL34 side of one AC coupling cap .25V ac dropping to about
0V and on the other side .25V upping to .3V on volume drop.
Replaced that one nearest the heat build up and its match.
The pair of 220K in blacked glass sleeving to -12V is to " stablize the bias until the
tubes have warmed up enough for the self-bias to take over.
It adds about -6 volts to the grids" soon after switch on.
One HT cap had bad solder. Replaced weak input socket.
Beware earth continuity is through 1 only pcb standoff
and beware of trappping loose wies against standoffs.
EL34s use ac on heaters, 12AX7 s use +/- 12V DC in pairs
33K large dropper, bad solder points and overheating, stood
off the board with heavy duty pins, also 2x 1K, 2x100R, 1K.
2 canted 072 because of large Cs.
Mains 7R // 29.5R,.2/.3R,.3R
o/p 113R bn, 103 bk,// be/gn .9R, Y/W .3R with o/p set to 8R
Not returned in 4 months of use with passive venting mod, for fan
retro-fitting, so presumably my venting mod was enough.
From a USA user
"I came across a thread on cooling issues with an Ashdown Peacemaker
I bought a Peacemaker 40 in the US. I have experienced
issues after a few hours of having the amp on.
At one point I use to put a window fan behind the amp while we played!
I thought about mounting a fan as well but I would prefer not to cut
a hole in the outer cabinet if possible."
Ashton GA80 guitar amp (Australia)
RoHS date of introduction for Australia ?
Anyway 1/4 inch i/p socket too weak even for domestic use , breaking up in a
few years ( within RoHS regime), no obvious datecodes except main electros
seem to be 2000, otherwise maybe 2004 or 2005 IC dates. No-name flimsey junk
, the type with 2 insulated change over contacts. On trying to work out the
functions, apart from the tip contact/grounding setup there is a line to one
of the isolated switches that grounds at plug inserted and o/c when removed
, it goes DC connected to the base of a pnp SM1015 transitor - function ?
If it kills the gain for bang-less plug insertion then it would only work
for insertion , not removal, as that switch makes before tip makes/breaks
Luckily the owner wanted a reliable input socket and was unconcerned about
the loss of the plug-in de-thump cct. To replace the domestic headphone
socket (has isolated switching) would have been a work up as 0 or 15V on
that control line so could not use an effects pedal type ring switch action.
And the ring switch for a normal stereo 1/4 inch jack is the wrong action
for here anyway, requiring an inverter somewhere or one of those awkward and
rare offset 1/4 inch switch actions. cct proper, holds off full gain for 0.5
seconds or so after plug insertion, all the while removed 30dB or more gain
drop via 15/-15V control into the first amp. Although no obvious PbF solder
problems the original input socket had thin+wide blade pins going into holes
of that wide diameter and loads of filler solder, asking for problems with
ordinary solder let alone new-fangled
More as a reminder to myself, for the next time this problem appears. A work
around without having to cut into the existing cct to put in an inverter.
Use a small SPDT relay (+emf diode) with power adapted from whatever
Permanent ground on the flexing ring contact in a 1/4 inch TRS socket and
the fixed ring- contact to the low side of the relay.
The added delay, due to relay action, only adding to the desired effect of
delaying the removal of the gain suppression until after tip contact is made
( unless someone is very slow at plug-in)
Uses 2SA1941 ,2SC5198
7815 , 7915 ? not seen
220R for phones
That SM1015 base goes from 14V to 14.6V in each state
and Col 14.7V to -14.8V
Audition spring-line amp
Excessive white noise.
Germanium technology low power practise amp one time
sold at Woolworths with detacheable 15W speaker.Replace
the input side transistor 2SB440.
Seems to be a notorious problem with fan system on these, so many I cannot
find a recognised solution in amongst the complaints.
Monitoring V to the 12V fan takes ages getting from 1.2V to 3V and stops
there as fan starts taking current at 3V. Already the h/s is too hot too
keep fingers on. I never liked the idea of slowly ramped V to fans but will
ask the owner if they want the temp monitoring changed or fan on all the time.
I'm reluctant to bend thermal sw back to reveal the other face as pins
look semi rigid and probably not marked anyway.
Not so straightforward a work around.
Mark the 3 screws with nylon spacers before dismantling h/s
TO126 C3205, Q15
TOP66 C5242 Q24, TO220 A1837 , Q14
8R cold over R64 at mains
1R over R63
.9&.5 "diode" over Q24,25,26
1.6&/5V "diode" over Q21.22.23
s1 th sw NK 1.1 with Q25&Q26
JM65RC TO220 Q27, A1837 Q28
Active monitoring with a TO220 device
LM35DT, linear output, and perhaps JM65RC means selected for 65 deg C.
Plenty of data on them but will have to sketch out the LM35 and 2
transistors to see a way around dropping 65 to 40 deg C in effect
The self-tap screws supposedly holding the IEC socket to the chassis have no
bite and so each insertion/pulling of the line cord plug, stresses the PbF
solder joints on the pcb carying mains voltage . Solder OK at the moment but
looking a bit suspect already and so a year or two on ,a conflagration in
the making. So remedial solder and bolts and captive nuts replacing the
The cut out sw is nearest the hottest part of the h/s so cuts out before the
fan drive has really got going, it still has to cool down the bulk of the
heatsink, all the while the underside is still going up. I can see a diode
going in "under" the LM35 to raise the 0V output for 0 deg C to a voltage
that will at least turn on the pass transistor to the fan, at room
temperature, and then increase it with use. As it is the heatsink gets too
hot to keep fingers on (50 deg C?) before the fan gets any voltage at all ,
surprisingly 24V but 3V will start to turn it.
A great advantage with always-on is that the user knows the fan is
in working order right from the off.
I tested the cut out sw in situ. I can just make out markings through
the insulation wrap.
028 A 20 161
perhaps 161 deg F
Sw goes o/c about 80 deg C and s/c again 65 deg C
marked 028 A 20 161
Don't try this amp with no heatsink attached as the quiescent current is too high
without heatsinking the o/p devices
If the amp is left switched on with no input the quiescent current is enough
to slightly raise the h/s temp to about 30 deg C and fan comes on now
I suspect the problem is drift over time of the Vbe of the drive transistor,
change of 0.01V there leads to change of 1.5V on the fan , so if Vbe rises a
few mV the fan will only come on at 50 or 60 deg C, too late to be safe.
3x "17 deg C "/ 0.17V of lift from 3 SM shottke diodes under the sensor is about
right to get the fan turning properly at ambient 15 deg C or more.
.27V over shottkys (.44V at DVM measurement) and .25V from sensor gives about 5V on fan
.17V one shottky not enough
.29V Ge gives 1.24V
.55V Si diode is too much
Definitely a PbF solder amp from 2007. Made in China for USA for export to
the UK but presumably the same for domestic USA use , no mention of PbF on
pcb or rear of casing
3.3R, 2x 10R
"harwin" connectors have locking pips on the long face end cheeks
33R from +60V rail
Vs from R41 near umbilical
Fan stabilised with o/p of .57V [.3 (ie 30gegC)+.27] and fan having 7.7V, room temp 21 deg C
Load test 400Hz , 5.8V ac over 4R
22.6V over fan
.23V , .66V on combined sensor output
Behringer maybe rebadged Alto
eg Behringer MDX2200 composer Pro near enough same as Alto ACL2Pro
Behringer LX1B-PRO , Bass V-amp ,2003
Behringer SL2442FX PRO , mixer desk, 2004
This 24 ch mixer has been "repaired" twice for a very rare random fault.
months after being "repaired". Loss of L channel output at the XLR. Previous
person had obviously looked at the most likely suspect of the 1/4 in sockets
for insert , with bypass contacts and XLRs thmselves. Remove graphic panel buttons
before removing main pcb
Both Main/Sub push-push switches, 4 pole C/O are very suspect in the FX
sections, half a mm pushing when out will loose the effects component of L
or R channel and a bit more, full loss of one or both channels. Any other
suspects to check?
I'm surprised the schema are out there but minus smps so some details taken,
just in case.
switcher driver ? (reverse of pcb not explored) maybe designated
04N68, TO220 , usual 0/O possibility (obstructed viewing) other marking
googling around turned up
"Incidentally, on more than one occasion I have repaired a Behringer with
this exact same symptom (no L ch), and it turned out that one of the main
runs right at the far right edge of the PCB from fader to output jack socket
section. When the PCB was installed into the chassis, something sharp
caught on the PCB and partially cut through the track, which eventually
failed some time later."
Got into that panel now
Although no observable damage to that trace, I may as well run a line // to
this trace while in there. Looks like that mod, replace the 2 4p c/o sw ,
the 2 1/4 in sockets for Insert and at least remove the main slider ,
Putting some alternate sets to the pins of the interboard headers, and keep
After that, should it bounce, I suppose its a matter of building an active
buffer and LEDs as telltales , half way through the outer stages, to
localise down a bit.
I will try and advise the owner to swap to using the upper channels , in
case its a problem earlier on.
Force on the 0.25 socket L insert sw about 700gm, to break contact, about
1400 gm on the R to break contact is a bit suspicious. Normally I would
expect problems in the order of 300 or 400 gram contact force. Found a pair
of 4w c/o switches to fit in the 13.5mm of clearance space.
To desolder the no-name black 8x8x12 mm 4p c/o switches you need to sling .6mm wire under the sw
body and pulling when desoldering. Normal clamp force over the body is
enough to break-up the casing of these very weak switches. At least I could
see inside and no wonder they're problematic.
Remove 2 side cheeks and 1 sc each side under
Leave 2 ps sc in place in square recess and remove 2 sc at the IEC, open and disconnect
ps from pcb.
Excessive hotmelt glue on cons , pick off with a dart point before breaking.
Remove the ps to make more bench-friendly.
Bend the 2 prongs to release phantom sw lead.
ps 180uF, 400V, bowing top
270R, R27, 470K
T1 clip protruding so bent back so 270R can be pushed away from the NV cap, held to the clip
using a loop of silicone sleeving
Master slider 10KD , 1/2 track 90% , log
Removed both Insert 1/4 in so and pushed 14x10x1.5mm into behing bypass contact and glued
ps ribbon in phantom mode
Replaced both 4p c/o with Secme doubled up miniature rotary sw. With wires to the pcb holes
under the replacement sw , just about room with the 13.8mm of clearance between
pcb and front panel (brass standoffs)
Sub posistion is lower (end of front) when sw pushed in (as original)
electret microphone is right next to the PTT sw
Beware of misaligning the TRIM LED on edge of pcb
Before fitting the main pcb back, make sure the shield for the digital board is fitted.
No R op now, with test signal , signal at in and out of both L & R insert socket but not
at top of MAIN slider or MON slider.
Tape out L&R ok
I'd fractured a trace at the insert soldering.
Chirps and hash on phones output due to bad contact at large ribbon IDC connector.
Replaced the IDC inside of the original with a plain unpolarised one and cut off the original, enough cable length
Added a large cable clip bolted through the convenient hole in the pcb to clamp
the centre of the 40 way fixed IDC at the othe rend on the op pcb. Check it clears the ps.
Check all 40 ways are good. 4 chances each of L and R signals failing in passes through this ribbon.
To replace the chassis back leave the 2 slotted sc at the ps loose fit until the IEC and sw are in place.
Place a large cheek sc in each end for temporary alignment for the small sc
Returned later , the above problem resolved but now loss of FX 1 function
FX1 present on Aux Send 1 out.
Select subgroups and FX1 signal there.
If the memory push action stops working, remove the knob and screw up a bit of paper
and push insid ethe knob - it was bottoming out against the panel.
Main-L out of FX1 on 4w sw connects to Main-L of FX2 at its corresponding 4w sw
Cross compare FX1 and FX2 / main / sub sw in all 4 combinations for a broken
pcb trace or via. Not seen as left the pcb in place and 2 wire bridges used instead.
4 end poles of th emain/sub sw 4w sw, go to 4 track ends of the main Stereo pot.
pins 1,4,5,6 with pins 2&3 to gnd
IC53 Inverts INVERT line L &R
Beware of the metal shields under the DSP pcb as it is floppy and could short components.
Big Time practise amp
failed mains fuse assembly
uses D1406 and B1366 , 2x 0.5R, 4559
Blackstar Artisan 30, 2008,ROHS
4x1K on EL84
20K between pairs of G1
40 percent mains fuse ok and HTs
about 60 percent and sound out
100 percent mains, all electros with 8R load
all mid pots
10mV 400Hz in Hi, 3.1V over 8R
Fuse holders in awkward position and messed up cap and bad contacts.
To remove requires heating back nut to melt lacquer.
Assumed intermitant making was blowing fuse although no reported noises.
Boss BCB-60 effects pedal board
Is there a problem with the 1/4 inch sockets on these? Especially the input
one that must take a lot of guitar lead yanking. They are the flimsey
domestic, no name, hifi type things and used vertically at floor level so
any stage crud gets in them.
Intermittant through-signal drop and I cannot induce collectively or
individually and will have to check the internals of all 5 pedals plus
daisy-chain leads etc.
Although metal mounting bushes on these sockets, it discuises the fact that
all behind is flimsey plastic. The one taking the in-use strain had its tip
contact displaced outwards relative to the other one. Making contact, but
presumably not reliably under temperature change/ grime etc. I replaced both
with standard robust plastic bush sockets wired together and space made for
them , being somewhat larger. And checked the internals of the 3 out of 5
otherwise suspected pedals, and leads.
Looked inside the board output ones as well, because leads to them could
have been tripped over at some point.
footprint space 12x13x27mm, so small, a justification for use, logo
something like HT curved to fit inside an absent semicircle and type numbers
variously e/b/a/h/g. Sighting through the barrel the tip contact should be
in line with the centreline (centre of ground contact) but the stressed one
was 2 to 3mm off line. The rear plastic closure square will come away on
releasing the pawl. Grotty PbF-looking soldering on the output interboard
Both i/p sockets (as daisy chained so either could be used for lead
in)replaced with manly ones.
Another amp roday will have a manly 1/4 inch chassis mount socket replacing
the pcb mount failed one.
Boss OD3 uses M5218
Boss TR2 uses M5207L01, 3 M5218
Ibanez TS9 uses TA7555
Boss BR600, digital recorder, 2006
Q47 an 8pin SMD presumably a powerFET switch, with an erupted hole in it. Marking
probably ?? as 1 or 2 missing characters
3 connected pins of the IC go to batt -ve, single pin via R2 a fusible resistor of .3R to batt +ve (9V), and 4 pin combination on to the rest of the circuit via the on/off switch.
Quite a bit of space to fit something bigger than the original, but what sort of rating or identity and then data for a BB??F1 top code SMD ? So far not found an 8pin BB powerfet identity
but no identity of the powerfet,
www images swamped with external views of course and 1 out of focus pic of the diode fudge in the above thread
The Service Manual identifies it as VEC2302
Dual p-ch 3A,30V, buried in the datasheet Marking: BB
With the ex-SOIC off the board then traces are consistent with the pinout of that IC with both devices paralleled
Both devices are in series:
S1 -- D1/D2 -- D1/D2 -- S1
1 7 8 5 6 3
This is in parallel with the not fitted D2, so you can just fit a diode in
position D2. Maybe a Shottky.
D2 Anode ----------- D2 Cathode
I was going to put an IRF9532 in there as plenty of space for a TO220 but I've no idea what the seriesing is all
about so a couple of paralleled shottky SM diodes went in at D2 pads
Owner lost the original plug in ps, and tried using another 9V one of the wrong polarity.
I changed the connector and polarity and the unit worked for about 10 hours and then bounced back.
So something to do with reverse polarity stressing or knocking out one powerFET initially but continued for
those 10 hours with the other one or something like that
It does not say regulated but I had checked it initially and it was 9.6V,no load, and as rated .5A then probably
good enough. Original Boss one not known
Talking to an engineer familiar with solar PV controls. He was reminded of the anti-shadowing bypass "diodes"
in solar panels. Otherwise a shadow over as little as one cell will kill the output of the whole array, so as little
as a good dollop of seagull shit is all that is required. Say 50 cell panels and each sector of 5 can be bypassed by
one of these 2pin powerFET devices built into each panel , output falls in a sector below a trigger level and
"diode" kicks in bypassing the 3amps or so of the rest of the array but only dropping .05 volt, so overall array
efficiency drop of 1% instead of 90% or whatever with the shadow of a chimney or telephone pole or whatever.
PS pin is negative
With no lead then battery wiring is connected to the power in socket.
Previous leaking of a battery leading to corrossion of battery terminals and no battery
]operation, when working
Green fuse is Tyco 7X7 marking 7 overlaid pair of Vs inverted 7 , resettable .7 amp
Boss ACA adaptor must be 15V or more
using 9V supply is too low. 7V dc on battery is too low
Changed the 220R 1/8W on ps line to 35R cold ptc thermistor and 10V zener
Boss DD3 digital delay foot pedal, version 3B , 2003 ?
Does not always latch on, momentary footswitch seems ok eg physical
switchpoint, zero ohms on , the latching is via RC and taking an input to a
Mark all the 1/4 sockets before removing as their orientations
Original problem was probably (from sooting/tiny etch mark)
the electro (too long lead had touched the adjascent
ground line so cut it back)at the 5V line of the SM 5V regulator marked "A E" , IC9
I don't like the indirect footswitch ground line via 2x 1/4 inch
sockets and casing but nothing loose.
placing various Cs across the sw made no improvemnt.
Desolder the small pcb off the switch so the metal casing can be removed for
ease of working on after demounting the sockets and pot board.
Did a subcircuit determination
Using one wasted, as paired-up, input to one of the SM 74HC00 gates ,
cutting just one pcb trace and added an R,a C and a D constructed a 0.4s
monostable, pulse stretcher so now latching properly. It does not seem to
have affected the hold mode option either.
Footswitch goes to ground to activate, with input lead connected.
via 100 ohm to pin 1 of 74HC00, linked to 2 (H via 100K), 3 to 4, 4 to
12 and 13 and red lead to hold option on mode sw,
5 (H via 100K), 6 via 10K to pin 62 of main IC,
8 to pin 59 of main IC, 9 to brown lead and hold option on mode sw,
10 to 11.
Soldered 1M between pin 2 and 14, cut trace between 1 and 2, then
.47uF SM cap from 2 to diode to pin 6 to conduct when pin 6 is low.
Latching failures seem quite common with DD2 and DD3
according to the archives.
The line to the led had been squashed against the power-in socket.
The input socket switch only functions with battery power
Roland BOSS DD6 effects pedal ,2002,(no repair but did create a noise generator , see tips files)
Dropped into warp mode of its own accord then failed to
move out of bypass to any mode
Originally thought the mode switch/pot was flakey because about 12K
left at the end of the track, not knowing internal endstop, so beware.
Thinking bad contact could make the mode selected be "0" , the warp setting.
Mode selector switch on a Boss DD6 effects delay peadal. Looks just like the
other 3 green case subminiature pots each marked B50K , by Alpha. Nothing
external to indicate the 7 posistion "switch" is different. Inside a second
properly molded-in internal endstop as well as the normal one, so track is
limited to 3/5 of normal full track.
So if wiper breaks, due to grease, then pedal has a mind of its own which
mode it wants to be in. When cleaned out measures 0, 3k, 8.1k, 13.4,19k,
25k,30.6K in the 7 positions and over full track 48.6K.
Pot used as a mode switch yes, with vague areas around the knob designating
the mode but not ever seen a dedented pot before. And how are they assembled
at manufacture.? Externally there is absolutely no different appearance
between the "switch" ones and the pots, I've looked under an inspection
lamp, no odd dot in the molding or any other difference. If you turn the
shaft then it clicks into the dedents, being the only difference, but that
is not visual.
functioning as a switch, relying on high linearity and
non-variation of resistance for firmware interpretation.
There is a difference to the pots, they are ink stamp marked 2G on the side,
this "switch" one is marked 2H7
Laid out on a clothes peg and mm rule. Third part is the track section
inverted to show the second green endstop. The fourth image unclear in pic,
as buried in the body, holds the dedent wiper. One detent that shows is to
the right of the purple > and the endstop arm marked A
testing the 9V line , ohmic, varying 150 to 250 ohm
and drawing well over 55mA spec current.
unidentified ps components
Perhaps voltage regulator or bucky controllers
5 pin , size of body area, 2.8 x 1.5mm, SOT235, IC9,
Overheating ps components
same physical type but top code
4 pin on perhaps a pass transistor, size of body 4.3x 2.4mm, IC6
(number one not I) and printed as 2 pairs , Q15
Replaced with sm BCW67CTA , to proceed.
BJSQ replaced with a LM317 set for 3.6V as the datasheet for
the AK4352 DAC said maximum ps was 4.6V but was driven up to 5V
via Q15 and DAC and ADC seemed to run ok at tehat and
probably suppoosed to. So don't know what BJSQ was , perhaps
a supervisory IC. Back to some useability but still
somewhat high consump[tion.
Testing 9V line now , probably as it should be,
Diode check 1.1V / 0.6V and on R like testing an elecrolytic.
Test connector pins
1 gnd, 2 pin 19 of IC5, 3?,4?, 5 IC7 pin1, 6 2100 supply, 7 ?
ucontroller responds to function changes correctly but audio output stays at
bypass. That u sends data that varies on function change to pin 63 of a Boss
proprietary 100 pin. AK5353VT ADC sends data to pin 68. There is data flow
to the RAM but otherwise nothing comes out. The AK4352VT DAC is ready to
receive but nothing there. This main Boss chip runs warmer than should and
more than the 55mA consumption , in specs
In this non-working state and deliberately feeding with 7.4V
and not 9V, the 5218A supplies are 6.6V and the 2100
like the main chippery is 4.3V, probably should be topped out at 5V
, regulated with full 9V
Boss GT-6B multiple guitar effects pedal board, 2005
Two of these known to the owner of this one have shown the same symptoms,
but never connected together in any way.
The other one apparently corrected by a factory reset (coincidence?)
At switch on the display continuously scrolls as though one of the up or
down bank select pedals
is active, ie looks like the action of someone continuously turning the
rotary encoder switch.
Have taken apart but not reassembled yet , unenclosed .
Only 0.2mm differentiating first touch to click over of the very basic click
switches under all the
foot pedals. The "wah-wah" switch is different action. Is it a stock fault
of deflecting steelwork/pivot wear/bending pcb/expanding soft inserts?
causing engagement of these switches, then just washer packings to correct
for a short time until the problem re-emerges) or something more
electronic/software or internal rotary encoder problem
Not a stuck sw problem. Unlikely rotary encoder sw problem as physically
rotating it changes the 7-segment display but the auto scrolling error
function does not. No susceptibility to touching components. Select a
funtion like tuner and the display stops scrolling and gives tuner display.
Disconnecting all ribbons except the display one , the scrolling display
still there so a main board problem seemingly. I suppose ESR caps check is
first port of call. User manual from Bossus site and schema etc on e-service
I asked, at receipt, whether this one had been connected to a pc and it had
not. I've just asked whether it had been connected to a sequencer and so
maybe the other one had as well, transferring corrupted code. This 6B same
as the e-service 6 pdf as far as display is concerned , buffers between uC
and display seem to be operating correctly but still scrolling with the
switch and rotary board disconnected. No obvious ESR problems, little much
else to do, check a few V if 6 and 6B agree there.
With all ribbons disconnected other than display one I noticed that the
display stabilised if "digital" fingering of the empty mainboard socket for
the ribbon that goes to the sw board and pair of analogue mx chips.
Reconnecting that ribbon the display still scrolled but tugging on the fixed
end of the ribbon stopped it. Resoldered the ends and display and overall
functioning seems normal, eg up/down bank buttons function, unlike before.
Nothing obviously wrong with solder or the crimp? terminals to the wires
that are also the solder points but something wrong there. Not PbF but
resoldered all 4 such ribbon fixed ends JIC. As maybe generic Boss problem
area they are no-name white "Harwin" 0.1 inch type connector system for
discrete wire ribbons, same crimp? system at the fixed end (inserted into
the housing then soldered to pcb) and socket end , so standard sockets at
one end and solderable thru-housing and pcb pins at the other.
So is it coincidence the other one was playing up the same way and was
genuinly cured by factory reset or same wiring problem coincidently
disappeared for the present on that one? Or of course some other
intermittant problem with this one coincident to fiddling with one
connector, the repairman's dilemma. Repairing (or not) by divination in
I've now had word back that both units have only been connected analogue to
amps and guitars, no midi or digital connections. Not bought from same
LCD ribbon, line 6 disconnected, top line of pixels only on,ditto line 4 and 5
2x4051 ribbon and display connector then no scrolling. Remove 2x4051 line
and scrolling returns. Same scrolling with all othe rribbons
connected, but not the 2x4051.
Before dismantling the wah-wah, if necessary, monitor the pedal force to
return it as found.
Boss ME50 multi effects pedal
All LED flash on &off then latches up with the seven segment display
showing the decimal point only. Removed the single board from chassis
No stuck sw, no bad solder joints seen, no bad ESR caps. One time only,
pressing on area of pins 1 to 20 of 144 pin Boss chip the board started
responding to switch pushes, not repeatable since.
It will read data from the EEPROM always, so can read version number and also can do
factory reset. Sometimes it will function, responding to switch pushes, from
switch on. At least a full service manual with all data lines etc is on e-S.
All datalines between DRAM and uC have continuity, in area where there sems
to be pressure sensitiviyt. Now to power up and check some DCs
Leave 3 pedals in place and remove 6 rear screws to remove pcb
Annoying rattle on moving is nylon rings over the LEDs
Reset IC M51957B6P topmark 957B
10uF across existing 1uF and delays reset by 3 sec from .3s
67.7MHz just observable on 20M scope
expression pedal .1V to 2.7V range , 3.3V
8.9V in 7.3V at IC9
7.3V at IC1 supply
3.3V on all pots
dot in 7 seg display means manual mode but no further response
IC3 codec p10 22uS pulses
p12 2.5MHz , p11 11MHz
IC11, p16 active when responding to sw and any pot turning , never activity on DRAM
Decided part of digital signal processor chip faulty
Boss ODB-3 bass overdrive
Sometimes fails to work or stops on battery and sometimes on adaptor.
The plating on the power socket metal parts was breaking up ,
presumably interfering with the switch contact as well.
Boss PSC 2036 broken and lost UK dummy pin
9V 1A smps
3mm a/f recessed screw under the label.
Could not find 3mm spinner so ground slot into the head (and plastic)
Now know what PPO (Polyphenylene oxide) smells of when burnt
a pungent tarry phenolic smell.
Maybe swap the housing next time . Robbed a pin off a scrap
wall wart and cut a fare face to mount to casing. Opened out a guide hole in the hollow centre of the pin to
take a screw and also superglued in place .
400V 33uF, ER401 diode , 1A fuse, NEC 2561 opto, TO220 TOP223YN,
zener ?150? (obscured, 105 deg caps 470uF 10V, 100uF 15V
Bullet VM30 combo, GDR from 1990
But looks more 1970s . Pull+slide
the covers off the handle to release and springline
"X2 080" ,"X8 761" ,"TL 761" (not opto) ,"X8 082" ,"X6 081" ,"X6 082" ,
B080D = TL080
B081D = TL081
B082D = TL082
B761D = TAA761
V4007D = CD4007UBE
the X* numbers are datecodes
2x KD607 80V, 10A, SD339 and complement SD34?
SD335 , 336 on preamp , 2x330R , 120R
An E-line size or varicap type package of a diode like SAY32
marked 32 VV or 32 YV, 32 volt zener ?
The ones marked 15 are the zeners for setting the
+/- preamp rails. Works for 1 second and then fades out.
There was a burnt section of the ground track between the
secondary ps side of the preamp and the signal side.
The grounds of the 1/4 inch sockets were measuring 6V.
Bridged temporary with 68 ohm and measured .6V so
bridged with a fuse holder and 1.6 amp
Probably due to
operator "error" and have replaced with a fuse there.
Fusing current of approx .16x.8mm copper strip about 7 amp
Eventually in use this
fuse failed gently, so replaced with a 2.5 amp antisurge
The siting of the ones marked 32 maybe for overvoltage sensing , but not
normally in service.
Probably those are 32V zener.
There are 2 more of that package on the preamp.
These labelled 15 X4 and next to the +/- pass transistors for the preamp +/-
rails so probably 15 Volt.
Springline 315R and 10R, if the 10R one is disconnected there
is distortion to the output with reverb set to zero.
Repaired now, but for the archives there is a safety issue with these amps.
The earth bond wire to the amp chassis is fine but the bond to the front
panel metal is very poor, just a brass rivet to the phenolic of the pcb, of
a few ohms drop over the years. Needs redoing to the metalwork properly.
Top handle screwed into the reverb tank so leave in place.
Lost rear bolt anchor. Hot melt glued in place a captive nut
Burns Orbit Three , 1967, ser no 40*
loss of ch 1 and ch2 over the years , broken handle
someone had disabled Tremolo and Reverb at some point ant too much missing to
14 Ge transistors and 2 zeners
o/p Tx KB1923
2/2/4R across the top between the 2 paxolin tag boards not along the boards
TR3 near TR8 NKT404
TR15,TR14, missing?, TR13
TR17 (near intensity pot) , TR16
Black scale rings under the knobs are glued to the facia , heat with hot air
to remove and to replace (removal required to undo pot nuts)
Bad vol pots leading to loss of ch
Someone had replaced TR4 with Si NS BC1547351 ()BC154 of 1973 ? )
3 x Jensen C10R sp, 2 measured 11.9R and 1 11.4R
Original core was 7mm sash window cord , sissal so broke of course. Clad in
sewn thin leather which had failed as well . Main handle thick leather with
figure-of-8 x-section. Pulled and pushed out the glued core and thin leather
from the main handle to reuse the thick leather part.
5mm polyester guy cord , 4 turns threaded singley with stout wire through
each side of the handle, through the cab fixings and also 2 pieces of heatshrink.
Heatshring large enough to take the 4x polyseter and small enough to slide in
plain run of the handle, the othe rrun is lapped to sew-up.
Tie off the ends with an extended "knot" and push into the overlapped run of the handle
so wedged tight but next time may add some hotmelt string for the heating stage.
Balance up the 4 turns of cord. Encourage the heatshrink out of the other run , through and around
the fixtures and return into the other handle run. Centrally posistion the handle.
With something wedged under the handle,
heat the heatshrink with hot air
Carlsbro, late amps, linked with Laney so check via google images for similar kit the schemas.
Carlsbro BassBeaver, 20Kg
Broken pin on input socket, desoldered but soldered
wire to the remnant and soldered to the nearest component
While in there noticed a burnt 2W resistor that was o/c.
This was a snubber at the speaker output consisting of
1uF,100V non-polarised electrolytic and this resistor.
Remaking the remnants of the R it was about 3.9 ohm.
Nothing on TDA7293 product pdf. Replaced with a
2.5W, 8.2 ohm with long solder joints along traces.
As probably o/c for months obviously not too critical
The R-C combination is a Zobel network
"can be quite important to the
correct operation of the amp. It's purpose is to neutralise the inductance
of the speaker voice coil, with the intention of flattening its impedance
curve at the HF end. However, without this network in place and doing its
job, I have known output stages to burst into spontaneous ultrasonic or even
RF oscillation. The values of R and C are calculated according to some
esoteric formula that I'm sure real audio buffs could quote at you chapter
and verse, but the general rule of thumb is that you start with a resistor
of equivalent value to the voice coil's nominal impedance, and then
calculate C from there. " - Arfa Daily also http://sound.westhost.com/highspeed.htm#a33
+-41V, uses TL071, 072
Resistors 150 ohm, 2x680 and the unknown 2W
Carlsbro BassBeaver, 2002
Zobel 4.7R 2.2uF 50V unpolarised
150R, 2x 680R, C547, BC546B
Gain pot is set back so needs a starwasher and the grounding loop.
Dropped then nothing
ok on receipt but bad rear send bypass so replaced the socket, cut the solid wires
to release,and rewire in 2+1, 2 to stubs and 1 to pcb
Carlsro Cobra PA100. 1992?
Cuts out due to send return bypass sw
No op but pa works inserting signal
+/-15V on all 072
With test signal at input and xtal earpiece then signal on send so moving
contact but not the static one.
1 thin and 1 thick bush washer on each control
Carlsbro Cobra PA100
Blowing mains fuse . Under test the LED would noticeably dim if insulated 600R mic
in low Z input in one hand and other hand brough near to speaker will introduce
50 KHz oscillation and excess main current draw. 50nF across PA input dropped o/p
50 percent at 10KHz , perhaps 30nF next time. A lot less prone to
Carlsbro Cobra , 1986, 28Kg
Someone threw something at this speaker in a Carlsbro Cobra combo.
It works with distortion, like a weakened form of one of a pair
of complimentary drivers working only.
By digital probing (using my fingers) at about 4 o'clock position ,
unpowered, the rubbing resistance feel to movement of the cone disappears.
Same if powered up, no distortion, to a power level where the effect of my
fingers damping comes into play.
A liquid that will contract on drying to paint radial stripe on
cone and dry and test, repeated until problem goes plus one or two more
Or would freeing the rim or part of the rim of the cone by hot-air heationg
and reseating all or part be better.
If part then release 2 to 6 o'clock say and pull or 8 to 12 o'clock and
push, my guess is pull would be better.
The central dome was buckled in so attacked this first. Drilling a few 1mm holes
and using a dental sickle brobe managed to pull it back into reasonable
Somehow that corrected things, just a small puncture in the cone periphery
to patch over now.
Uses 2x 3055, 2x1C03, 1C04, 2x 10R, 2x 0.24 , 150 ohm on phones line
in the pa.
1C04 misread as IC04
TL071 s , 2x680R , RC4136 on pre-amps
+-44V dropped to +-15V
Someone had been in there before and managed to disable the reverb.
The transmit side of the springline wire has no earth return, just a dummy
pad on the pcb. That person had soldered the braid of that wire connected to the receive
ground to the driver output.
Tracing the RC4136 quad the spring line driver output is
pin 3 o/pA via 100 ohm to springline and 220p+100K return to
"A" i/p and via 100 ohm to i/p(D). Receive side of springline
connected to pin 9 i/p(C).
Carlsbro Eclipse 12, 1998, 12 ch mixer amp
Drummer laid his snare drum brushes by the side of
the amp and the wires flicked into the vent slots on the
side and killed the amp except for front panel lamps.
Replaced 2SA1668 pre driver, and FS7 fuse and
added "crockery scourer" grill cloth inside the vents either
side. Also for personal H&S cut off all the jagged
corners on the sheet metal work with double
pa uses MJ15024 / MJ15025, 2x 2SC4382, 2x 2SA1668 , 2x 4580,
TL071, BA10393 , 4093
digital board TIP132, 7805, 7815
discoloured 220R ?, measured 265R over each in cct.
Disassembly, remove side panels, remove top
and then divider panel
5.7V, -15, 15, 15/5/50V,
47R in cct, 2x 10R
PL4 for LCD display panel
PA works with all mixer panel disconnected
main bridge rect ac 102V, 138V dc
othe rbridge 18.8V ac
Carlsbro Equinox 8150DSP, 2003
Music stand fell on to the sliders area and snapped off the stems
4 sc to separate amp and mixer
break nail varnish before removing ribbon
cheeks , 2 pk under, 3 m/s sides
knob colours G,3xR,2xB,W ,then R/B/B
top panel 9xpk I/O area and 11x m/s
4x star washers on the top 4 so only
Slider logos YD in a circle, A503 according to the user manual , ALPS probably rotary pots only.
Tried gluing back the stems but failed removing knobs test.
Headphone L is stereo
Could not find stereo pots with same physical footprint etc , as usual.
Robbed the sliders from a couple of pots with near enough the right size
sliders. But the required tracks are L,W,W,R (W=wiper) wheras all
the ones I had were L,W,R,W. Melted the plastic swaged "rivet" to remove
one contact strip and mounted it back the other way and remelted with some added hotmelt.
Although this worked the physical height was less and the leading edge of the wiper would
touch a pcb rivet , 10% from 0 and 100% ends of slideway as the whole wiper tipped in moving.
Cut some 1mm thick PTFE strips to lay under the slideway , ove rthe stem to pack out to stop the tipping
and also ground down the rivets a bit on the touching edge to give an incline.
Carlsbro GRX7, 1996
Smashed vol pot B10K, broken inside
Red tank conn, nearesr Cab edge
7815,7915,VR on master panel
Carlsbro GRX7, 1996
Sometimes failed to work and sometimes dropped in power
All the 1/4 inch sockets needed attention, front and rear.
The signal pa/preamp interconnect lead needed attention
The subsidiary +rail 156R dropper needed replacing.
Uses 4x MJ15024,
2x SM2177A, 2x SM2178A, CBC182A, BC212
1C03 , 2x TL071
156R, 5x R33, 10R,2x 4R7
Mains primary 6.9 ohms
uses +/-15V regulators on preamp
Carlsbro Hornet 45 lead, 1984, 17Kg
Distortion. Problems with output transistor, poor joint at
base for some odd reason, heatsink hold-down bolts not tight
enough. Soldering generally did not look very good - flux
residue problem? - re-did all power handling ones.
Uses BDW93C, BDW94C, RCA IC02, RCA 1436
Rs one measured in circuit as 156 and 2 not larger than 0.3ohm.
Put a union in the speaker cable for ease of repair.
2 pairs of side screws at rear release the rear
panel and front ones for front panel release, springgline
fixed to centre board.
Unusually the amp separates into 2 sections separately connected to the
wooden casing and so electrically isolated as far as any earthing.
The mains transformer is on the rear panel which has a proper earthing point
from the IEC mains inlet.
Power supply is plus and minus rails but the common is not connected to
ground at all. The power and signal lead to/from the pre-amp / reverb is 4
lines : plus , minus , common , line level signal with no earth connection.
The front panel is connected to the common , not to earth anywhere.
There is much more noise immunity from general stray pick-up if I run a wire
from the earthed back plate to the front so bridging common and ground
but left as is.
Interestingly this unit was yearly PAT tested and passing presumably earth
bond and insulation test each time.
If they had checked insulation resistance relative to the front panel , he
assuming it was earthed, then could that have caused damage.?
Carlsbro Keyboard 150 , 15 inch combo from 1985
TO220 devices marked 40871 and 40872 and also SM are presumable RCA40871 /2
, anyone happen to know what the TO3 devices are , presumably NPN ,
cold test seem ok. Usual Carlsbro, locked behind rivetted heatsink,
otherwise prea looks like HH Marlin type amps
I should know the identity of the TO3 tomorrow , both NPN on rechecking.
Loose Collector bolts so I have to get to the other side to tighten. Not
rivets , looked superficially like aluminium rivets . On Googling ,maybe cct
similar to this admirable effort at unravelling to a schematic, the Stingray
Even more like the Stingray. 2x MJ802 , 1 BC182 and 3xBC557 instead of 3x
bc212, 100R between B-E of MJ802.
Soft blown (not blackened) ps fuses and mains fuse , then abandoned for 10
years, no recollection of original failure scenario and nothing found, cold
so far , a likely culprit
Prea ps droppers 2x 680R
PA 2x.1 approx, 10R, 150R
Don't remove the TO3 -C bolts as not captive. To remove PA pcb
Remove 1/4 in so nuts, bridge rect bolt (heat solder points and push down
the pins to relieve any stress in the pins of the bridge rectifier, regular failure point here) , undo the 2x h/s,
and undo the B-E terminal blocks . As loose screws here and one collector nut probably the original soft blown fuse
problem. Refix with laquer. The blocks need holding back or they swivel , on tightening the terminal screws
ch1gain pot and main pot needed attention, usual Carlsbro problem of excessive grease inside
the pots , getting on the tracks, not wear.
No reverb function due to excessive Al corrosion on the tank sockets, leading also to
a large amount of hiss in the o/p
Prize off the spire nuts to release the tank and replace with normal nuts and a dab of nail varnish.
Accutronics 4BB3A1B 24R i/p red side, 207R o/p black side
Touching tank o/p pin induced amp noise. mid controls and 50mV 400Hz in and 4V on the tank input line
without tank connected. Cleaned off all corrossion .
Carlsbro Marlin 6-150 m2 1987
Insurance write off -not working after being in a room with a serious fire
not associated with this amp.
Some minor radiant heat damage and smoke stained but failure probably
generally relevant to other equipment in similar circumstances. Although
there are no ventillation holes with these amps there was considerable smoke
deposit on the inside of the amp. The concentration of smoke must have been
so great it had penetrated through the 1/4 inch jack socket holes. All these
sockets needed cleaning but the real reason for not working was smoke
entering the mains switch and IEC integral fuse holder and insulating the
electrical contacts. Power devices 2 off MJ802 ok . To gain access remove
one case end face,slide out top and bottom pannels after marking and
disconnecting springlines. Remove the rear heatsinks to get to the power TRs
that unusually B and E fix into screw terminal blocks on the pcb.
Carlsbo Marlin 8400
Run for 3 days powering 2R speakers, saved by 5m long speaker leads probably.
But not be break in the mains cable.
So if repeated breaking carrying mains current , depite X class cap
over the mains switch , would that be a more likely reason for the failure.
? Back EMF going well into the KV, punching through the insulation in the
primary section. Failed primary and exploded mains fuse.
Tx data core 2.35Kg 54.2mm thick with plastic tape cover , and 108mm and 54.7mm diam with tape.
47V , 5A inner wire 335gm outer 350 gm, 1.45 mm diameter.
Primary wire .95 mm ,
3.5V, .1A, CCD ac supply 10 turns .3mm
Carlsbro Marlin 8400 , 2002
exploded mains fuse after running the amp on 2 ohm speaker load
Tx primary measured 150R, variac at 20 percent jumps to high current.
Tx blown , probably bifilar wound, certainly chinese made.
Carlsbro Marlin 8400 , 2003, 400W mixer amp that immolated itself.
Remove the front panel first to work out which screws on the back
Q319 is a high voltage TO92 ( totally burnt and erupted
but 2 isolated lighter blobs on the remnant of TO92 face are in the position
of the isolated printed 2N of other 2N5551s on the board) then the melted
blob component goes from the base of this feedback transistor to the speaker
output line via the relay and choke. But it was 2N5401, (from the obtained schematic)
which did not have a match elesewhere. The
board is also burnt so overlay for this blob also missing. Anyone ever come
across a metal oxide resistor melted to a 3mm diameter blob like a small
tantalum. Metallic grey blob that measures 40 to 150 ohm or so across
diameters, was 1/3W reistor of 330 ohm.
The thermal heatsink monitor tranny was also exploded but as the face was
gooed to the heatsink, that face was spared from charring/shattering and
that was 2N5551 also, the thermal switch is 105 deg C.
The subframe inside the chipboard casing is held to the chipboard with 12 x
4mm bolts, into clinch nuts on the outside covered with the black vinyl.
2 had dropped out and because you carry this kit vertically but use
horizontally, plenty of chances for 1 inch long steel screws to roll into
the power amp.
But only plain washers and not star or spring washers under the heads
and no varnish /glue spots over the heads to stop any undoing.
On reassembly all internal bolts were replaced with star
washers and glue spots.
Audience were treated to piles of smoke erupting from the
back of the amp - Hendrix was more impressive.
Plenty of other damage but identifiable components for the others.
3 .5R, as well as above items and even
a 5mm wide , current reinforced with solder, track had burnt.
Copper trace 3.5 x .02mm and as 2 half approximated elipses of solder then
area of 1 elipse of tin+lead which is Pi x a x b , a and b minor and major
axes of .15mm and .8mm.
Copper fusing current of the trace = 12 amps
Lead+Tin elipse then 6 amps (not as much as I would have intuitively
Total 18 amps so 18/4 = 4.5 amps conventional fuse rating.
Presumably the circular to sheet allowance would up this 4.5 amp figure ,
but by how much ?
What sort of correction factor for thin sheet/non-circular heating then
I had a play with track width calculator
and assuming it is still sort of valid
at very high temps.
Putting the melting point of copper of 1080 deg C then for 3.5mm strip of
presumably 1 oz copper then the rupture current would be about 48 amps
which seems reasonable. I knew it must be higher than 12 amps as that
calculation was for round wire. By 1080 deg C we can forget about the solder
I think, assuming they survive ordinary power-ups a few times, I'll settle
on a mains side 4 amp anti-surge , with a 5 amp A/S ready to hand spare and
2 off 10 amp quick-blow in the DC lines.
Oriental script on the mains transformer and on a schematic.
Q319 was 2N5401 and the R was 330 ohm. I'd not thought about it but VxV/R
heating with single rail of amp voltages of 65V to melt a 1/3W resistor, not charr
or explode it, it must be about 300 ohms or 10 watts dissipation.
Uses 47V-0-47V ac, 3x 2SC5200, 3x 2SA1943
2SA1306, 2SC3298,2x TIP41C, TIP42C
2K, 6x .5,5W 2x 47
Replaced output trannies with lower voltage, higher
current but much cheaper TIP35C and 36C
and 2SA1668 to 2SA968 and 2SC4382 for 2SC4159
On bench tried powering with half rails of
+/-30V , too low for relay to click over and
no load at all. TOP66 of shorter form than
the originals so ground split some standard
spring to heatsink retainers and ground a small
notch in the end to engage with the mounting screw plus
star washer and glue dab and sprung against the
tranny body (with glue dabs) so using existing mounting holes.
With these lower rails
.3, 30, -.14 and .8, 30, .3 on "positive side" TO220 and TOP66
.8,30,-.3 on thermal feedback TO92
.13,-30,-.07 and -.4, -30, .13 on "negative side"
Full rail voltages not measured.
+/-15 V on the separate TO220s
With amp outside cab but in normal vertical
position and 7V ac of 400Hz driven into
4 ohms then temperature of thermometer clipped
to the top of the big heatsink stabilised to
27 degrees over ambient in 35 minutes.
No need to remove all knobs etc to acces the
preamp control section of pcb.
The master volume slider pot "knob" was
broken , owner used a match.
Plenty of sideways room to keel the slider
over to glua an extension to the side.
A bit of black cable tie bent and glued
to double up in a vice. A bit of a bend in this
piece to roughly match the leaning pot.
Desolder the 2 pins on one side to lean
over and introduce back into the cover and
resolder after positioning better.
Carlsbro Marlin 6 150 IV, 1995 ?
prea 2x 1K
pa 2x 0.3R (in circuit) 2x 10R,150R
TO3 nearest signal IP line probably NPN
Beware the effects switch at the rear can
give this "fault" as well
if falsely engaged. All pots
"worn" to the extent that its harcdly possible to
find a position on any of them to pass a signal to
the amplifier , so effectively dead when the
main vol control becomes extremely "worn"
as probability of blindly finding 2 active
spots in a pair of controls with 90 percent
defective is unlikely and pretty
useless if found anyway.
This occured at a period of cold weather
which may be contributory.
The pots were not worn as such. Believed to
be the original lubricant had hardened over the
active pot surfaces. Renovated all 8 gain pots
and treated the bass & treble pots with meths
bathing , both as per tips files.
Carlsbro Marlin 6-300 Mk 2 1986
Blowing fuses. TR7 TIP41C s/c all round,R (R21 ?)between C10 and VR1 burned but
probably 1K,R29 burnt replaced with 100R, other damaged Rs R9 22K ?, R13 3.9K ?
R14 1K ?,22K ? preset burnt out. 3 of the 4 2N3773 defunct.
As an interim replaced power devices with 4 x 2N3055 while
checking out biasing section before replacing with 2N3773s.
This amp had been repaired at least once before so cannot be
sure if correct components or voltages but from repaired amp :-
Thermo feedback used a BC182B, unknown CBC640 small BC182 type body in 60V
section of circuitry. Other devices RC4136N and TL072 .
Driving 8 ohm load DC voltages reading from heat sink side
on track side of board.
then row of TIP41C,42C,42C,41C
Carlsbro Marlin 10400 , broken effects code switch, glued stem to
basic plastic PCB mount hex codeswitch which only a marginal knock/heavyhandedness
will break and of course fails inside the sw so cannot change with a small screwdriver
as no purchase left.
Electronics similar to Laney CD850S.
leave 4x large screws on front panel . Remove 2x3 on sides and 4 large under,
inner case slides out.
"Digital" 7 segment number on overlay 200935 , not 2009
Remove 3 sides cover before breaking laquer and 2 x screened leads. Mark all leads before
removing including spades behind mains panel switch
pin8 of digital board binary1 then 4,2,8 and C is pin 24.
See tips for beefed up codeswitch details.
Check with owner what number on the front was the setting and check the 8,4,2,1 switches as
unlikely to agree numbering.
o/c powertone speaker , ITF, 6.4R
replaced with Eminence Alpha 10
mains tx 21R, 1.8R
6sc around main section
disconnect umbilical and both speakers, blue to main panel
discon prea gnd
remove 4 front grill sc to pull out prea
Tx 10.3// .9R
2x MJ802, 10R, 2x 1R 5W, 2x 10R 2W, .24R
2x 1C03, 1C04 piezo horn and 5.3R speaker
Carlsbro pm12, 1998
Hum and vibration crackling and sometimes , PPI LED
Speaker cons loose also
Feed XLR panel into cab, release front grille and end PS/PA
panel to reassemble outside cab.
loose gnd points, bad 1/4 in i/p so.
Bad solder to Zobel L, and D3, and bad PA-PRE cable socket.
Y is 0V line
R31 2.2R o/c but not discoloured so fusible R and someone perhaps connected something they shouldn't
Loss of frame gnd continuity as loose pot on the front
Carlsbro PM15, 2001
Dual purpose 200W PA head or a foldback monitor.
Reported occasional loud bangs and pops without any signal
input, otherwise no distortion. Of course I powered
up and with any amount of banging of cabinet no induced problem.
Took apart ( need to remove the 15 inch speaker first )
and powered up with twizzle stick and serious
bangs and whistles can be induced by tapping in area
of electrolytics C1 (4.7uF,63V )and C3 (47uF,63V) and
2 small signal MPSA92 all at input
from pre-amp. C1 probably AC coupling from pre-amp and
C3 local DC rail decoupler.
Otherwise no dodgy looking fuses, spade terminals
hotspots or suspected dry joints anywhere.
Replaced the caps and resoldered the trannies,
removed Cs seemed ok and one trannie pin/solder
did not sweat properly , contaminant ?
TR3, SM2178A voltages, -59,-0.6,-59.8. 2 possible dry joints
on this TR3 so added insulated heatsink tied to the pcb
with cable ties.
45V ac on both fuses
60V,-60V on bridge rectifier
uses TO3 devices BUZ906D & BUZ901D
power to preamp 15.6V,-15.6V dc
3 sets of 8 screws, machine bolts on speaker, washered
screws on front grill.
Carlsbro PM65-100 , 1991 stage monitor amp-speaker , Carlsboro
No repair as problem was in external feed.
In exploration a 100R resistor next to TR7
was charred but functional,replaced with 1W.
Replaced S M marked pnp TO220 trannies 1C04 with TIP41C
and npn 1C03 with TIP42C.
( for 1C03 use RCA1C03 and RCA1C04 for 1C04 to find data )
Supply rails +-44V
Carlsbro PM65-100 , 1990 stage monitor amp-speaker
Loud buzz plus hum and no power LED on front.
Someone had been inside and fiddled because they
had moved the header to front board one place out.
So + feed not connected. Still a buzz when put in
correct position or disconnected so presumably original
problem was on main board. Erroded "dry joint" on -ve
pin of the bridge rectifier so
remade all pin joints.
TR3 marked S M and 1C03 ? ICo3 ? 1C03 ? IC03 ? replaced with
TIP42C as seemed to have been running hot for no heatsink.
Carlsbro Sherwood Classic , 2002
Reported consistently low power
1994 JBR 23/2/1994 on the overlay but component dates seem to be 2002
and appearance more 2002, ser no. 80021.. (002 part =2002?)
2x MJ802, 2x 680R, 5W, 10R 5W
2x .24R 5W,
2x 29.5V, 2.4A Tx
2x .1R 1W, 2x TIP41C, TIP42C
8x TL072, 1x 071
philips C547B, 2x C556B, 2x C557
4 top cab sc plus 1 on Tx side
Cut horn cable and put in a connector, slacken reverb cable cab clamp
to release cable and unplug from tank, red to cab side
return bypass contact cuts amp
Poor clearance between prea pcb and chassis, resonance in use would easily allow it to ground out,
without any pot nuts slackening, added spacers under
main caps unglued
3x zeners probably say ST and not 15
B-E DVM-R of 100R on the 802s so perhaps cct similar to Stingray cct
sc 4 at top and 2sc L&R
With rear pwer level at max and pots at mid , GN-A, manual
400Hz 5mV in , 2.1V over 8R (main speaker line)
4KHz , 8.4V over 8
1KHz , 9.1V over 8
10K 50mV over 8R
No problem found , on further querying , the owner expected feedback when using the guitar
close to the speaker, he was not aware of the Phase control
Rear HF cut, cuts the horn out. Needs celluloid sheet around chassis
to insert amp into cab
Carlsbro Sherwood ,1982
Parametric gain pot bad leading to bassy growl noise
Bad send bypass sw kills amp
nut and bolt missing from bridge Rect, replace and resolder pins relieving stresses
Bad pot track rivet + grease
2x 2N3055, 2x10R
2x .24R, 2x40871, 40872
BC182 ,3x BC557
wires to tank are crossed over and if wrong way round bad noise with turning up rev pot
tank 43R, white 184R
no maker name, single conductor tails, bits of pcb show at phono sockets, both sides grounded.
Remove amp front grill 2 sc and the panel with sp falls inward , so support on undoing.
Carlsbro Showman parametric/1 , 1990
Blown fuses, shorted power rails used in very damp or wet conditions many
rusted and seized bolts
pa much like S600M without the triac cct on mains primary
3 blue and 2 or to other thermal sw
C-E short on 2x MJ15024 and spalled .33R vitreous coating
prea 2x560 ,2x270 2x15V
mains tr 1.4R/0.2R
Broken pair of output terminals. Replacement threaded sections too short
for direct replacement. Had to heat up and bend the pcb to angle away from the rear chassis.
Removed the fan delay switches as owner preferred to know the fan was
working at switch on and always used loud.
Red polyester .33uF, 400V between base panel and pa 0 rail.
Terminal strip R 5, Gn 7, Y 10, Bk 11
2x 4u7,63V TIC263D, bidirectional diac/zener?, 2 caps ,47K, 2k2 on speaker protect cct
2xSM2718A,2x SM2177A , 4x .33, 10R 1W, 10R vit, 4588 on pa
Beware stray wire filaments at the terminal strips
bad 20mm fuse holders
other ch 3way o/c SM2178 on o/p board replaced with 2SC2516 could not find a BUT11A or 2SC2373
powered up ok without 8R load but with 8R drew 1 amp of mains at 70 percent mains
terminal strips DVM wrt pin 7 when rerpaired
With mains at 55% main rails +/-30V
1 channel good the other one even with a 27 ohm load oscillates at 65
percent of mains and above, bursts peaking at 40 KHz dropping back to much
lower f, extinguishing and restarting over 5 seconds or so.
power amp probably much like Carlsbro S600M
uses 4x MJ15024 , 2x SM2177A, 2x SM2178A each ch
predriver DC levels (prior to oscillation) certainly different to the good
ch but no obvious reason other than rain got into the amp
A lamp will go in each of the +/- rails before I fiddle again
Removed the triac speaker prot cct just in case a reaction with that, same
result. Checked ESR of all cap types.
Upto +/-40V rails , below oscillation, all DC agree near enough on both
channels all TO3,TO220 and TO92, zeners.
Go up to about +/-45V and the 6V, 5W bulbs start glowing that I added into
the supply rails , alternately swapping dim and bright pairs very odd. Next
I'll disconnect 1 of each complementary pairing of MJ15024 and see what
Still oscillatated with one pair and also with the other pair. Checking over
the board again there was no continuity between line level i/p ground and
the pa ground. An innocuous 1/4W resistor the same body colour as all the
others but overlooked at 2.2 ohm bands was o/c linking the grounds. No
discolouration except I managed to originally see the third band as yellow ,
not gold. No overheating on the adjascent pcb , so presumably a fusible
In hindsight the slow "hunting" effect of the osc giving alternate loading
to main + and - rails should have suggested a ground or zero problem.
The "good channel" also had an o/c 2.2R but presumably because full o/c no
The failed one in the oscillating channel had 3.7K across the ends so
presumably not fusible resistors. Must have been a very high current surge
to knock out normal MO resistors without any sign of overheating.
Disc 1 input is sleeve of TSR of 1/4 inch socket, Disc 2 is normal tip
Carlsbro S600M, 1981 600W slave amp
Triac mains power protection, thermal sw on heatsink plus other stuff monitored
presumably. Its in an awkward area to get to, a lot crammed in a small box.
Carlsro badged TO3 audio o/p devices ERD1159 ERD apparently means Emitter Ring Diffused
and MJ15024 is reasonable replacement.
All h/s screws needed tightening but all unplated. Distinctive feature all
sockets on the back XLR ,4 i/p and 4 speaker o/p one set of 4 female and
other male. I cannot, cold, see how this setup works
I'll have to desolder one each of the pairs of the th/sw (4 in total) , one
pair for each ch , seems one parallel pair for normal fan use (in series to
mains fan) and one higher temp parallel pair for overall cutout via mains
triac. As all seem to be s/c cold, perhaps one of an o/c-cold pair is
shorted. Then there is a triac crowbar on each output that presumably
activates the mains triac, 3 triacs in all, to confuse matters
So 2 n/o 58C th/sw in parallel for fan operation and 2 100C n/c th/sw in
series for cut out. Can power up now having sorted that conundrum out.
Power side works including the over temp th/sw system, now to somehow
reconnect the signal lines. Unfortunately another problem became apparent.
To avoid a 1 turn secondary on the torroid they passed the coach bolt
through a second anchoring plate with some insulation. Looks like 2 cut down
black plastic 1/4 inch socket outer rings. One either side of the hole in
the plate, but of course not high temp plastic and have softened enough to
deform , not actually making metal/metal contact but obviously not safe.
Cut some PTFE discs to go inside the large hole and 2 pairs of
sheets of PTFE either side to bolt down 7.6mm and 12.1mm diameters
100R via mains sw , due to triac cct
primary 1.6R, sec blu/y .3R
2x 47R ww
SM2177A +1 inside heatsink section
SM2178A + 1 inside
4558 each ch
TIC2360 as speaker protectors
2x 1500uF, 63V
remove 4 screws outside air filter grill to demount
whole power block
118v DC R/Bk at bridge R, for 228V on variac, later
emerged this high V was due to triac control problem
I was running on a variac and with about 90 percent
mains and with no load etc there was 0.1 amp current drawn from the mains
and a noticeable amount of transformer noise I took to be saturation noise
and current drain, more than I'd like but until I could confirm with the
owner about previous useage, I let be for then. This time I powered up and 1
amp being drawn with no load at only 70 percent mains. Disconnected the
secondaries from the amp and still the same.
Disconnected triac circuit and the transformer is happy to 100 percent
mains, fed directly, and only few mA of current drawn. What can be going on
? To get to the triac componentry proper requires a major strip down first.
Could it be half cycle firing and causing some sort of magnetic
mutual/resonant/self-induction effect that is causing excessive current? A
matter of isolation transformer and scoping some dropper in line with the
primary to see ? No obvious heating on the triac, only a small heatsink. I
was monitoring the DC last week and it was already a bit over the 63V rating
of each electro. This time direct to mains, no triac, it was much more
normal, forgot to note but about +/- 55V probably at 100 percent mains
Scoped the secondaries and a cross-over distortion developes on increasing
the variac voltage, not particularly strongly, but definetely there, and
increases with voltage increase and "saturation" current/mechanical noise.
Placing an isolation transformer on the primary with a 25R/20W dropper to
"neutral" and scoping, then the problem was obvious ,now unfiltered by the
transformer. Could now run up much higher variac voltage because of damping
by the added R but even then there was 3mS duration spikes of peaks twice
that of the mains ac pk-pk of mains (UK) 20mS period. So some sort of quasi buck boost
inverter effect going on. What to look for around the triac when I get to it
?. To get to triac area, 8 XLR connectors with 3 stout wire standoff
conductors each to cut,
(then desolder both cut ends and replace eventually ). Because audio input
and output and mains control all on the same board with no obvious isolation
band between the sections
I replaced the BC214 with a BC212 and as no TIC236 to hand , with a TIC226D
for proving purposes, temp. There is now no sign of the broad spike trying
with the 25 ohm dropper, even to 100 percent mains. The 214 tests as 420 hFE
and I'll assume the triac is faulty. My triac test is little more than
go/no-go, as only substituting in a lamp dimmer set up, so may well work
with light duty and non inductive load. The 5.1V device tested as a 5V zener
, I wonder why 2x 1N4005 and not 2x 1N4001 in that area.
This is probably the circuit, split primary is used , ZD is a 5V,1,3W zener
, V are 1N4007 checked ok, 2.2uF,250V polyester ,
pnp BC214 emitter to top , 94R is 2x 47R in series
need equi-spaced font selected to read the ASCII image
| mains primary
|C------- 120V ac---------------------------------------|
| 47R |
| ___ |
| -|___|-| |
| /´ | |
| ,´ | |
| ,´ |< BC214 |
| / -| |
| / / |\ |
100R,25W| ,´ / ------- |
| ,´ / | | |
|----- / / | V 2.2uF , 250V |
.-. _|_/ / | - || ___ |
| | V_A / V ----||------|___|------|
| | | / - | || 94R,10W
'-' | | ZD | V
|----| | | -
| | | |
| --- --220uF
| 220uF --- ---
| | ___ |
600W audio amp, runs perfectly happily if this triac
stuff is bypassed. Soft start circuit
Plenty of gain on the pnp, all Rs check out ok and triac
checks ok tried out in a dimmer circuit.
Running up the transformer , without any load, with this cct via a variac
there comes an ac voltage where large peaks are produced at the primary and
overvoltage at the secondary and nasty saturation type noise from the
windings. Checked waveform on a scope via isolation transformer and
monitored over 35R resistor placed in series with the primary. Peaks are one
a cycle (about 3mS of 20mS UK mains) but not at peaks , troughs or inflexion
point of the mains and amplitude of the peaks maybe as much as twice the
mains peak to peak .
Swapping the TIC to a lower rating TIC226D the amp (no load) works fine, no
nasty mechanical noises.
Swapping the triac to a TIC263M 25A, 600V the same effect is observed. I'm assuming
that something is causing the triac to cut , once a cycle, when a high
voltage is across the transformer and the inductance of the primary is
generating these peaks.
As the 2 220uF,10V were high ESR I
desoldered them, to replace with new, but because new and old were short
pinned radial format, I managed to solder in the old ones again.
Replaced with 2 x 100oF,16V atop one another and shrouded
and fine with 25 amp TIC, so left in there.
Cut the standoff to all those XLRs to access pcb, replace
with new afterwards
In a closed steel case, no air cooling ( fan air is ducted only through the
power amp heatsink ) and no passive/convective vents.
Torroidal structure, no inherent saturation current with open secondaries
and otherwise well behaved. What sort of plateau temperature would you
expect if it was delivering continuous 600 watt ?
Rule of thumb: 1 degree rise for every 1 watt with an area of 100
sq.in. located in free air.
Assume 95% efficient transformer 30W!
Two layers, we're talking over 60 degree rise from outside air to
inside torroid. Just an estimate.
That was worse case scenario. I added a 110 degree C , 10 amp thermal fuse to
the outer surface of the tx. Should never be run at 600 watt and there is
some forced air ventillation as the amp heatsink is not totally airtight and
slight holes around the casing, but these transformers were made without
internal thermal fuse.
(A way to measure INTERNAL temperatures in a transformer without having
to dig into them:
Run until temp is stable. Shut off and immediately start
measuring winding resistance as a function of time. Plot the curve
and recreate the missing section of plot between t0 to t1, where t0 is
when you shut off and t1 is your first measurement. The resistance at
t0 tells you what the winding temperature was. you need to know
what the winding resistance was at room temperature to get a
Carlsbro Viper 1992
no compressor, no EQ
IC4 CA3080 , others are 4558
Corroded and broken 1/4 in socket
bad solder on comressor pot
3 sliders of the EQ corroded but renovatable, and no LEDs lit
Uses 1 amp rated TO92BC640 and BC639 predrivers to 2x 2N3055 , not TO220 devices
Cleaned all IC pins and graphic LEDs came on
IC6 p1 -14V, p2 -.003, p3 -2V, p5 +2V,.06,+14.5V
IC1 p1 0, p2 0, p3 0. p5 0, p6 0 ,p7 0
replaced IC6 and same +/-2V
pots at 1/2 and signal in passive ip
compressor at 0 , 400Hz in 50mV and compressor LED just lights
compress pot at 1/2 , 215 mV in and LED lights
pot at max needed 500 mV in
with all pots and sliders at half and comp and graphic sw in
50mV 400 Hz in
IC1 p1 and 7, .028, .32V ac
IC2 .25V, .32V ac
IC3 .25, .25V
IC4 p6 .11V ac
IC5 .24, .24 ac
IC6 -14V, +14V
with working amp
With all mid pots and sw in , 400 Hz in then .95V in and PPI
Carlsbro Viper bass combo, 1990 , 25Kg
Pops and bangs then drops out after 20 minutes,
starting ok again when cold.
Vibration induced failed dropper joints at the preamp 15 zener
supply rails. Redid droppers tied together with silicone rubber
sleeving and silicone rubber support pads and replaced associated
caps has one had probably leaked.
Redid solder joints on major leads on pa as
2 would soon be a bit suspect.
One 1/4 socket broken, the other weak , replaced with stouter
types , upside down and cros-wired and located in place
over the intrusive switch for one.
Rails +/- 44V , with back plate horizontal
and feeding with 400 Hz and o/p of 6W
continuous, then thermometer in the heatsink
back bracket stabilised at 75 degrees over
20 degree ambient after 40 minutes.
Uses 2 x 3055, 2x RCA 1C03, RCA 1C04
2x .24 , 22x 10, 1K 1/3 W
4x 4558, 3x RC4136, vectrol linear optocoupler
2x 470 ohm
Carlsbro viper, 1989
Buzz much worse on disconnecting the prea as no secondary ps
caps then. Loose main cap
Viper pa is supposed to be much like Colt 120 schematic
Carlsbro Viper bass , 1989
Dropped amp. Hum,hiss and thumping according to signal level.
Main rails +38V and +3V
Broken pin and failed trace to another pin of the bridge rect KBPC602.
Had to grind off the 4 outer rivelts and the 2 inner larger rivets , trice each
as the centre blob barred removal of the remnants
2x 2N3055, 2x .24R, 2x 10R, 2x RCAIC04, IC03-C,2x BC 212
1x BC182A ? indistinct
Extended the affected pins of the bridge with wire allowing plenty of slack.
Rivets replaced with 2 different sizes of bolts and captive nuts.
Carver PM 1.5A amp, 1999
Serious amount of damage on one ch from someone using handfulls of white
goo under the TO3 ," insulating" the pins as they were inserted through it
into the TO3 sockets, causing sparking at E and destruction of that socket and a
load of colateral.
Plenty of info out there
But nowhere can I find the ,no load, quiescent draw from the mains. I have
bypassed / isolated the mains triac board and powering via metered variac to
the transformer direct at these preliminary stages of powerup. Covering the pins of the
proper mains plug . Running at 50
percent mains about 0.1 amp current draw and all monitored DC levels match
between channels and clean signal on output and ps rails half expected
values. Increase to 60 percent and draw climbs abruptly to 0.5 amp . So far
quickly returned to 50 percent and nothing obviously overheating. Anyone
happen to know the expected draw?
I had to check whether I'd connected mains to one 120V primary by mistake as
it was that sort of effect but without saturation noise from the
transformer. Will return to it later today and also try engaging the triac
section as I've not got my head around the on demand draw triac instead of
good load/bad load or brownout triac
Very awkward wrapped-up around itself amp to work on. With so many supply
rails and 50 percent values I'd not noticed a blown up and shorted
3900uF,50V electro in the ps. Another 20 minutes getting that sub-board out,
anything to avoid taking the whole amp apart with all those 24 TO3 sockets
demounted , frail soldered-in interboard "headers" etc
Most Rs around R30 burnt up.
Q30 replaced MPS8097 with 2N3402
MJE2955T to BD912.
Replaced TO3 socket , replaced a number of the TO3 and pulled and cleaned
the goo off the existing over-gooed B-E TO3 pins
30 percent mains, high level distortion on pin7 of main interboard header array
-34.6, -15.3,-9.9, 20.8, 0,-8.0,-0.2
good ch pin 7 +0.2V
470uF was s/c
mps8099 ohmic replaced with 2N3906
40 percent mains DC at TL081 op up to 6V on bad, 0V on good
3900uF, 50V s/c in ps
disconnected R21 and R57 vand checked V
R21 49,8V and R57 -10.4V , 40 percent mains
Polyester 10nF C7 shorted due to radiated heat from failed adjascent R30, 220R
Reconnected both 4.7R and compared DC on good and bad ch at some main nodes
Change bias pot setting to bring down quiescent current on the repaired amp
50 percent mains +/-63V main ps
measured some main pa node V,both ch
o/p 0.0, -62.3, 62.3, -3.6,3.6, 0.0
at 50 percent ps rails +/-63V, +/-18.8V, +/-27V, +/- 11.8V
15V on fan supply
At 60 percent mains current draw jumps to 0.5amp, time to reconnect triac system
With triac/magnetic drive 70 percent mains and .21 amp mains current
First time of meeting this triac drive rather than protection concept
Upping to 90 percent mains the current draw drops from the 0.5 amp of 80
percent mains to .2amp approx and fan revs drop
100percent about .25amp , main railes +/-122V
.47V 400Hz in both ch , 9.3V over 4R each with vols set to mid
What is the prognosis for PAT/insulation testing of these "magnetic field"
amps, knocking out diac/triac etc ? with 3.9M, R8, between ground and one
side of the mains transformer. Triac protection ccts are isolated from
ground, IIRC, where used in amps. Survived previous PAT testing , 2M cutoff in UK
Carvin Pro Bass 100, PB100
Blown o/p , maybe started with poor solder,
hot spot, small burns at solder pads, device Carvin marked
60-72940 , replaced with TDA7294V
15 pin device to 10 wire ribbon
H2 15V,0,-15,sig to pa
H5 1 sig in, 2 gnd, 3 stdby, 4+5 + supply,
6+7 - ps, 8 mute, 9+10 o/p
Carvin Pro Bass 100, PB100
Any movement of the frequency pot for mid band lift
created full DC bangs. Ultra-miniature pots that have
next to no metal for the wipers. I assumed gooey grease
in the pot was sufficient to lift the wiper from the track which
in itself had no wear. Decided to replace the pot with sub miniature
pot but as overall length less, padded out with a block
hot-melted to it and board and extended connections.
Uses 4558s apparently dated 1983, although Carvin WWW
schema for version B dated 1995.
Used black 4 lead opto-coupler Vactec/Vactrol LED -ve at notch corner,
cell at the other end.
Used 15 pin hybrid 100W,100V labelled Carvin 60-72940,
2 large Rs, 820 ohm,7815, 7915
The rattle noise on moving the amp is a spare
fuse in the IEC socket.
The amp to speaker link needs the elbow jack
replacing with conventional, just enough room.
Poor mechanical connection at the elbow means
a resistance and voltage drop, heating the plastic
disc that is all that forces a mechanical connection
so progressively worsens.
Carvin X50B tube amp, 1989
Told the amp was not working
Amp seems to work perfectly well, being repaired for minor problem
, broken wire at the return of the external effects loop
so not working if externally connected.
no succeptibility to microphony or tinging distortion.
Testing the 2x EL34, gains are good and matched but after a minute on
heated C/H insulation check, the resistance gradually decreases to 1M for
one and 0.5M for the other.
What problems will this lead to if continued use, and how quickly ?
The amount of leakage apparently is no big deal for
power tubes, if it gets below 100K then have a hum problem.
I was wondering if there could be
some sort of thermal runaway situation.
Measured no more than 1mV rms hum over 4 ohm output for this one , level set
for 2.25 W of 400Hz output, but disconnected and monitoring for shorted
All pa W/W measured in circuit at about 350 to 380 ohm.
5 x 4558 , 4049 + 4x 4558
240V primary 4.3R
Secondary red , in circuit, 32.5R
blue / gn 2.2R
large gn wires heater supply
H2 wire colours
Bl,P, D Brn, R, Lt Brn, O, Lt P, Lt Blu, Bk,Y,Pk
470K , 10K
Someone had been in there previously , maybe removed
R arounfd the Master pot.
Could not see why they would employ just 1p 1w of
2p2w switch and no use of the pot.
Placed a 680K R where R13 on the overlay .
Load test , thermometer wired to a 85mm
pickle jar lid , balanced over the 2 bottles
4 ohm load, 400 Hz giving 3v ac over 4 ohm
15 minutes to reach 40 deg c over ambient
and 0.06V ac increase
Casio CZ 5000 1985 keyboard
No function,LEDs or LCD display
The only convenient 0V point for the TTL I could
find was the -ve pin of the ps bridge rectifier.
No 5V for the TTL. It looks as though the keyboard had been
dropped as the large electrolytic on the ps had moved and
consequently the track continuity to the 5V regulator part of
the ps was broken under the capacitor pin,not obvious at al.
With all 3 connectors unplugged and PA order on main pcb
not the ps end which is different order.
Casio WK 3000, 6 octave keyboard,2003
Intermittant loss of left speaker.
Attended to all ps/pa solder points and conneections
and desoldered headphone socket and remade.
Open case upside down , from the rear first
and then free the keys section.
Work on it upside down with the keyboard section innermost.
3 pin TO126, device marked S2003
marked D for diode on overlay , only 2 of the 3 pins connected and diode and
resistance test to the other 2 pins probably o/c so n/c ?
All else functioning perfectly, but seemed odd using 2 of 3 pins. A nice
stable 5V over the 2 pins in the ps area, so that
a 5V, 10W (with heatsink) zener diode was my assessment.
No heatsink used on this one but a useful TO126 format for say 10W zeners
that are bolt-downable.
Uses LA4636, 2x 2068,Sharp PQ1CG21H
NEC upD63200 dual DAC , pin 15 serial data in
Al caps 2.2V, 2.7,5, 3.3V , SM tand 0.8V
2x wired caps on uPD65881GK062 gate array on underide of large board 4.9V
Ami LP62S2048-70LLT 256x 8 SRAM
ps to main processor board ribbon , starting red
5,0,5,.2,,01,2.9,0,5,14.7,5,1.6 (o/p signal line 1),1.6 (o/p signal line 2),0,0,2.7
D shaped recesses in case for washered screws
On first powering up it plays dumb, display echos the key presses and midi functions normally but
no sound out of the built in speakers unless you wake it up going into demo
mode for a bit. Nothing wrong with mute/standby functions of the main amp
and low level hiss from the speakers so not headphone bypass problem.
Possibly on powering down "local off" setting for midi use is stored in the
Seems no access via the keybpoard/keypad/buttons etc to alter this, must be
via an external pc/midi link.
But just pressing "piano setting" resets a number of things , one of which
is setting local to ON (if OFF), in the troubleshooting guide , if you have
a silent keyboard.
This Keyboard not used via MIDI
But there must be some powerdown (or power up ) fault creating this random
occurance (left unpowered overnight and powered up perfectly ok, despite
deliberately switching off at the mains rather than powering down via the
power on/off button).
No obvious on-board battery , although overlay symbol and unpopulted section
of the main board has this for some other model type.
The corrupted memory is on 'song memory', keyboard ges silent after the
owner pressses that button to recall previous recordings.
Probably corrupted when writing to it when someone pulled the DC supply plug
out of the back.
Citronic Digi 16P mixer amp maybe 2007
Hopefull ps bad/burnt solder on a 2W ceramic resistor , double sided board
or not from the reverse side, the trace on the blind side, as obscured by
+/- 155V on mains bridge rect
Anyone know of the SWPS schematic or is Citronic rebadged as other names?
The SMPS controller (seems to be outputs via a few predriver TO92 to 2x TOP3
powerFETs across the rectified mains) a SMD IR2156S which according to the
is a flourescent tube electronic ballast and igniter, no mention of use as a
SMPS, with obviously no igniter requirement one hopes.
"American Audio" seems to be related to the Citronic name but exact cross
It should have been a simple job. Intermittant drop out. Look inside powered
up and the ps fan is obviously defective, so fits the symptoms. Fit a
replacement and power up and not a dickie-bird. No led flicker or fan kick.
Undo the ps and obvious dropper solder problem underneath. Sort that out and
still nothing by monting on pillars. Checked for topside mixer and power
side earth continuity if that is required. So what else have I disturbed?
close inspection reverse-side looks fine, topside is heavily populated and
very few solder points can be seen. Continuity to the pa monitoring
Enough power gets to the main bridge rectifier for startup supplies but the
relay does not click over that shorts out the droppers for full mains
current, let alone anything else.
This is a "Hailin switching power" DWP1070 power supply but that got me
From the IR datasheet Vcc is enough to get the controller started and both
control voltages are the right side of thresholds for operation so a mystery
why no oscillation.
The relay supply is taken back across the HV/LV divide, rectified from its
own winding on the switching transformer, so no oscillation , no relay click
I misread the datasheet , not enough Vcc for IC startup. Local vibration
from me must have been the camel's straw for a hot-side, luckily industry
standard voltage regulator once I could read the label, and its downside
electro, after having been cooked in service. Replaced and we have power
IR2156 p2 - p3 connected and p5 -p6 connected, following in fault mode
p9 to R16 SD <4.5V
p10 to R33 cS >1.3V
con 3 is just DC supplies
another time reading p10 <> 0 , p9 4.2V
R21 probably 33R had a corroded/flaked end
7815A VR, 23V on ip 4.3V on op
replaced it and low side cap 27V, 14.8V
fans -12.7V red to -12.4V
and bk -17.9V , nowhere near 12V
warming the TC1 seemed to make no difference only 5.3V on fans
+/-83V on main rails
LV HS device DC readings
BCE, -12.1,-2,-12.7V dc
Untwist pa power and speaker and ribbon wires
Now to take some quiescent DC readings on ps coldside and one of the
PA as there is nothing technical out there on these amps.
So fluourescent supply ICs can be used for controlling power amplifier SMPS
266R between PTC+ and - , marked TC1 near the pa ribbon cable
10.1K and 10.6K on reversing DVM probes on airpax ps temp sensor
Mains to 2x large black thermistors? which are bypassed the blue relay
contacts when energised
On demand 12V fan control
Under therrmistor control. If at power up the DC voltage is too low to start
the fan can you always rely on the fan starting at some point with a slowly
increasing voltage or does it depend on the make/design of fan ?
3 fans fed from the same varying supply. 2 large , one small, all nominally
12V. The 2 large start with the applied "cold" voltage and eventually the
small one starts with warming of the amp . Checked by slowly powering from
a bench ps a few tmes . But I randomly picked up another new fan that I had
about and once out of 10 or so times it did not start by the time it had
reached 12V. I decided as this amp was never used for low power use that I
would disable the ramping and set it on maximum drive always, not worth the
risk/inconvenience of stressed components/mid-performance chance of a cut
out. Q4 and Q5 and 2SD669 on hs is fan control. Added 160R to bring PTC cold resistance up to
460R but made no real difference. So made open circuit for full fan on voltage of about 11V
From start up mains relay clicks over about .5 sec in and pa relays about 2 sec in
Replaced the seized power supply fan with 2x 40 mm 12V, .1A fans tied together
using one of the original tapped holes and a piece of paxolin board to the other
tapped hole and keeping the fan bodies away from the mains side heatsink
Probably the worst bit of "soldering" i've ever seen.
An intermittant fault with one channel speaker lines 2.7mm diameter over the
insulation, 1.5mm or so core, the 4 wires go to a rear board for speakons
and 1/4 inch outlets. Each wire is stripped neatly , leaving some whitish
thin coating over the copper core wires that probably holds the filaments
together until solder temperature melts it . Pushed through the large holes
in the solder pads and "soldered" on the blank side of the board with little
blobs of solder relying on melting of the board composite to hold in place,
and unmelted coating plainly visible on the other side. I assume the holes
are plated through or there would be no electrical connection possible. The
assembler must have soldered the wrong side.
PA, red blue speaker wires (outside amp) with 8R on output
TOP3 DC readings
-6.2,-83.4, -5.7 x2
.5, 4.7,.03 x3
Q34 -6.7,-83, -6.2
Q in 3 columns of 8 , 5 and 3 off, outer pins only as tight to pcb
1.7,2.3/ 2.7, 1.1/-1.4,.8/ -1.4, -2 / -82, -81.4 / -82 , -81.4 /-82, -81.4 / .6, .06 / .03, .03
.03,.03 / 81, 81.6 / 81.4 , 81.6 / -82 , -81 / .6 , .06
0, .6 / .01 , 0 , .06, 0
Citronic SSL 1001 Sound-to-light unit
No lamp function on any channel
Fracture of a pin on 4025 due to corrosion at
juncture of legs and solder.Other ICs looked
similar so removed all and replaced with socketed
new CMOS ICs.Note for personal safety when
working on the logic circuitry disconnect from the mains
and power the logic between Vss and Vdd from a
10V bench power supply.
CME UF60 USB/midi keyboard
stuck control sw buttons
4 long screws on long side of corners
2 close under front large gauge m/s plus central pair, recessed are large pk hold keyboard.
Beware clipped on wire to underside panel.
2 x Zn pk under front brace then unplug and mark 2 wires before removing.
power-in board 3x Zn small to rear
2x Zn large to pillars
2x L7809, 7805
sw panel all Zn , 2 large standoffs
power i/p socket bad , ring of gunk in the socket, "reamed" out with 2mm drill
mark main pcb standoff pillar orientations as offset
Added 6 1mm thick nylon spacer washers around the main key pad.
Refix this end first of the long pcb , probably shifted wa scausing key jam.
The small pcb with 8 and 16 MHz xtals , 4 way conn is bodged into 6 way
conn shifter towards rear panel.
Stuck key via D to p15? + p18? (no obvious index pip)
power in board PbF needed soldering top and bottom
To stop Transpose LED flashing do a factory reset of Octave + Transpose
while sw on
Loud buzz all control settings
Probably "bathtub curve" failure as Googling this with TDA2030/A or hum/buzz
threw up nothing.
Or maybe swarf around o/p device ragged bolt hole so cleaned away the silipad
and replaced with mica and new TDA2030A. Failed p3-p4 20 ohm.
LM13700M as SMD with DIP conversion
Remove amp through front slot
Gets excessively hot
Draws 1.2 amp mains
At 85 percent a 6L6 measures
0,0,-5,0,-38, 377,379, .5
-69.1, -29.4 over R21
100 percent -79.4V at D17,D18
16V 10,000uF C64 domed end so replaced with larger cap needing shaving back J2 connector
If you can unscrew overhung screws then only the prea V pcb needs removing to change cap
Added 51K over 22K next to bias preset like the 15K of a BV120
100 percent mains and .8 amps a 6L6 measured
0,-4.9, 436, 433, -48.6, 0, -4.9,0
mains Tx 2.1R// Be 1.2, or-or.9, r-r 6.9, Gn .1
op tx 13.6, 11.4
Changed mains neon dropper
That was "lighthouse" neon 47K dropper for 110V used in uk on 240V. Same
with this one needing the mains switch changing , charred and part melted sw
cover this one but holding up at 47K.
This one been run too long with insufficient bias and run away red valves.
Crate BV150H, 2003 ?
Blown fuse blackened barrel, replaced and then intrusive hum developed
After testing all valves and on removing could see a dark opaque patch on the
inside of the glass envelope. Broke in by sawing off the bakelite locating
spigot and using a hole punch on the evacuating pip and found a bare metal patch on the
anode/plate , otherwise grey coating. Breaking into that there was a patch
of missing white coating on the cathode opposite this patch. Connection
between cathode and G3 is fused / broken link , presumably very high current
passage cathode to anode, what could cause it and how much current could
Before I broke in the getter was usual metalic black appearance
The getter in the cap is now white caesium oxide or whatever (in a sealed
bag i might add), the black patch is still matt black. A square patch on the
envelope, square because that was the boundary although not extending to the
glass, looking like a spray paint squirt but square rather than round
I would say the patch on the anode looks as though it has thinned but not
punched through, so perhaps the metal plus whatever the grey coating is
condensed onto the envelope. No trace of white in the getter on the cap
until a few minutes after I broke the evacuation pip in the base
The opaque patch was constrained only in the section of glass containing the
section of anode with the burnt patch. Neither mica spacers or plate metal
fully close the gap to the glass so any of this material could have gone
through those gaps but didn't. This sugests to me some sort of directed
jetting action. Normal more metalic looking getter cap coating at the top of
the valve was still present before I broke in. All 6 6L6 were of the same
batch and none of the other 5 had this side opaque patch
I cut the pins at the base of the envelope to see into that area under the
cathode column and the ribbon that connects to the cathode tube is spark
eroded ? to a break. This ribbon is 0.5 x 0.04mm in section, if it was
copper then the rupture current would be about 6 amps
Mains transformer g/g 0.1R, r/r 7.1R, or/or 0.9R, bu/bu 1.8R
o/p tx 11.4R/13.9R
pa 6x 1K, 2x 30R, .1R, 2x 150K, 220K, 4K7
preamp 6x 10K, 1R
Mains transformer wire colour coding probably like
Blue Voodo 60 (BV60) but this one 4.5x4x5.5 inches,
audio o/p 4.5x4x4 and no choke
With 7 mains primary wires set as Bl+w/w/bn/V and 199V as mains then
5.65 V on all 8 +6 heaters and 407V HT1 and well over 6V ac
According to owner , bought it off company rep a few years ago and is export
Blew a fuse a few weeks back , runs still ,after fuse change (self heeled
cap?) but excessive hum.
450V rating ps electros but I measure 488V on the HT rail and varying ac (4
to 5 volt ac measured via 1uF, 1500V polyprop), perhaps seriesed-up, but 3
The neon lit mains switch looks more like a light bulb , runs too hot to
keep your finger on, I suspect droppers for USA mains inside. No serial
number on the chassis
No mains voltage stated at the IEC inlet, just fuses for 110 or 240V, 7
wires to the primary side of the tranformer and jumper spade matrix inside.
As the rep was going around Europe , not just the UK .
Powered up and looked for voltages off from 0,110 or 240 .
No smoothing choke for this amp it would seem, unless its in with the mains
As the mains switch is made for 110V use then anything is possible
I should have said previously only the 110V and 230V fuse ratings stated on
the chassis, not 2 separate fuseholders, so someone might erroneously think
it was an "intelligent" ps , no external selector switch or helpful
labelling of selector matrix inside.
All valves test ok except one 6L6 which, apart from heater, is totally dead,
no gain at all at any anode current. There is opaque stain on the envelope
in area above pins 4 and 5, localised in that area, although it could pass
beyond the non-round, mica spacers. I assume some metal melted and
evaporated/jetted onto the glass like the getter process. I assume this
could have been plasma arc to anode and excessive current and blown mains
fuse, as that part of the amp history. What would have happened here ? I
will break into the base/glass pip/cut-ring the envelope and remove the
innards to have a good look as presently cannot see anything through the
deposit. A melted hole in the anode? what would physically stop any valve
action? the getter is still silvery.
Not yet retubed (that one plus another removed for balance) and tried out on
reduced mains yet.
Other than heater continuity it tests as though no valve placed in the
Same colour code of primary, not secondaries , as that blue voodo and
seemingly the same significances. But I'll have to take apart to check what
is jumpered to what, and also the HT1 smoothing is different as it uses 3 ,
not 4 caps there. I forgot to check each voltage on the 7 primary wires,
will do so next.
With the duff 6L6 and one other removed
Putting 199V on the existing setting of primaries gives 5.65V ac so
suggesting 6.53V ac if 230V fed in on existing internal set primaries. Is
6V ac on that Crate BV60 schematic a strict ie +/- 0.1V, or nominal 6V (with
all 14 heaters supplied presumably)
Also 199v "mains" gives 407V HT1
The hum is present but with my variac I can lift the ground and doing that,
the hum goes and amp works fine , normally testing an amp there is no hum
and lifting the ground can introduce hum , so I wonder what other problem
lurks. 1000V megga test on the mains Tx shows nothing amiss to ground.
Looks like the same colours but not necessarily the same taps.
Monitored the total primary resistance and marked, removed/replaced spade
connections until 3 spade connectors blue , grey and black removed without
affecting reading . Leaving blue+white stripe, white,brown and violet as the
Powering up on 199V wrt to neutral the free wires read
is this the setting for 210V, 230V or 240V ?, I'm trying to get the maximum
number of turns as the primary. I'm thinking I need to swap the blue+white
with the black lead. If complete agreement with that Blue Voodoo 60 then the
existing wiring is undefined on that chart, the J numbering does not tally
with this one
Broke into the 6L6 , I thought the caesium getter went white immediately but
takes a few minutes, envelope safely sealed separately now.
The outer grey metalwork anode had a bright metal spot adjascent to where
the black envelope staining was. Cutting half the anode away revealed a bare
metal patch on the otherwise white coating of the cathode, no pools of metal
or smoke trails, G1 winding looked fine. I'm surprised how tough the
mica/composite ? spacers are compared to similar I've seen inside toasters
Exploring the 6L6 a bit more there was continuity between the base pin and
G3 but the internal contact to the cathode was missing. Presumably a
deliberate weak fusible link in whatever occassions a plasma arc strikes
between cathode and anode.
Looks as though the hum was associated with the input socket. This is
designed to be isolated from chassis taking ground from screened lead. As it
was turning round with tight bush nut I assume someone had been in there and
changed the insulating bushes about so ground-looped, now isolated and tight
and no undue hum.
Looked under the pa board and it is 2 seriesed 47uF,450V for HT1 and the
other one with a dropper for another HT.
date 2003 or later.
Mains primary now set for presumably 250V as heater readings are still a bit
So with full mains on there and all 8 12AX7 and only 4 of the 6 off 6L6
reads quiescent 6.6V ac and 470V HT1 from 356V ac, other secondaries or/or
32.8V ac and bu/bu 66V ac.
Incidently not only the neon /sw needed attention but the handle is crap
and jagged sharp metal exposed inside, covered with nylon spiral wrap, then
expanding nylon sleeving and then 2 layers heatshrink all under the covering
I cut the pins at the base of the 6L6 envelope to see that area and the
ribbon that connects to the cathode tube is spark eroded to a ragged break.
This ribbon is 0.5 x 0.04mm in section, if it was copper then I make the
rupture current would be about 6 amps. Presumably failed at a weld spot so
less than that
Changed to black /w/bn/v probably 250V setting and 3 other leads left
taped over and tied off the board. And perhaps bk/wh/bn/Vi 240V and
Blue wire interconnect "ribbon" pa-prea
and white -6,7V
2x 4700uF,25V under pa board
As not 2 replacement 6L6 at hand, temp added 3.3R over the heater supply to
check and this gave 5.8V ac
Intermittant loss of throughput
Sovtek valves problem
Likely a commonly occuring problem on the discrete wire IDC connectors, this
one 2003. The core and insulation of the screened wire is too thick for the
IDC metal. Presumably the IDC metal relaxes and only marginal metal contact
to pass factory tests in the first place. Only light finger force required
to lift the wire out of the trap. The screening contacts are fine, as just
heatshrink sleving on them.
There are about 10 such screened leads inside , with an IDC on either end. I
suppose the probability of 1 in 20 failing is quite high.
1 & 5 J8 connection bad
ch 1 select sw
Technique for replacing 6L6/5881 o/p valve tubes
I have large hands, how do people with small hands/short fingers do it?
Just managed to break the top of one of these bottles. I thought I used the
right tecqnique but failed here. Sovetek, GT badged bottles , instead of
domed top, nominally flat with a bit of a central pip.
Come replacing I go in the sequence , along the line of 2,4,or 6 sockets,
that allows a full finger each side of the dragon's teeth grips to depress
while pushing in the bottle. Then I place with top of the valve in my palm
and push down on the ledge area of the top of the bakelite base, with finger
tips. Doing so , the palm of my hand is barely touching the top but enough
pressure on this pip to induce failure. As such a light force , I assume it
was likely to soon fail from vibration & temp cycling. Failed in the ring
around the flat area.
Next time I see flat tops (flat not compatible with vacuum) I will cover
with a temporary grommet, before replacing, any other experiences/tips?
Perhaps change technique to making a yoke to push down on the spring
retainers , using chest , forehead or chin or something, and then use four
fingers on the base to press into the socket. Or some sort of chassis clamp
to depress the clamps. Then two fingers, unless a weakened socket, is not
enough pressure to overcome the resistance
Or ignoring the scratch marks made on the base , and push in with 4 fingers
on the base, after all it is only cosmetic damage.
I don't remember seeing these sort of central pips before (on that end),
either domed or flattish.
Next time I will have a couple of strips of PTFE looped around the dragon's
teeth and push in with 4 fingers around the base. Then releive each spring
in turn to retreive the PTFE. If that does not work then have to make up
some sort of spring compressor or let them goiuge away.
It's just that years ago I came across an amp that the owner loved rotating
the bottles about and the bakelite was a real mess, barely functional
Serious mains hash noise, more than hum, especially on
the 2 non-clean channels.
Repeat problem due to those flimsey IDC connectors, see above.
A number of (variable) ohms in the ground path between
input socket and chassis. 2 screened wires and 4 IDC connectors
between input socket and a decent ground line.
Pulled back the pathetic plastic IDC sidewalls, stripped the
PTFE? sheathing and soldered the
grounds to the IDC pin. Not heatshrink sleeving as above , but soldered
both signal and grounds this time
Crate BV150H amp
Second one I've come across where the standby lamp thinks it is a lighthouse
( for a short while). When cooled down the neon's now black internal dropper
, 1/3W or so, measured 550R . The switch housing says "110V lamp", surely
I'm not the only one to have come across this issue. I don't have the
schematic for the 150 , the BV120 schematic has the neon on the HT ac side,
not the rectified and smoothed side. What is the work around , separate neon ala
Marshall valve amps etc. Low side of HT neon returned to odd valued 332K in ps.
While at it, the
mains-on neon is also set for 110V like the other BV150H . I'm in 240V land
and that will need accommodating as well. This one 2003 manufacture and
without attention, that dropper will go pyrotechnic in ten more years of
The paper label at the mains fuse says "U EXPORT 240 VOLT"
Strangely both sw marked Arcolectric , England and 110 lamp, generally only
building site kit would use this in England. Mains one discoloured enough so
impossible to read colour bands measured 47K so both set for 110V presumably
. Replacement ones have plenty of space to change the dropper, 150K as
original for 240V land , and the HT standby 150K dropper replaced with
o/p tr HT side 14.1R/11.7R
some of the cable /spade connections at the mains section for 240V
thin W, thin W, W,Bn,Be,W, thin W
red-red 335V ac
large R54 100R
using 332K R to ground then the HT neon can be 240V set neon
15K between V2 p6 to J13
100R 5W to 4K7
R55 to 10K R80 on prea via umbilical on line neares pa
256V , 236V at R80 on low mains
80 percent 345 and 291V
95 percent 430 and 356V
Standby sw goes between J33 and J38
o/p tr supply to J38,
relieve springs in screening cans
Crate GFX 65, 1999
Triple footswitch , no name , no ratings on switches.
Impossible to use as a mind of its own which channel it wanted to be in.
On resistance anywhere between 200 ohm and 100K on each of them.
At least easy enough to get inside them, dissolve away the grease and deburr
the rough edges and put back together again.
uses .2, 3x .47 plus 4
1.5K, 3.3K,220, 2x10
5x 072 TIP42, TIP47
7x J175, 3x J112
primary 11.5R , secondary .5R, 60V ac
Crate GFX 65, 2000
Green LED but no sound on Clean channel
Someone had been inside with a power drill or
something doing some "repair" and stripped up
tracks and board.
In particular the trace that goes past near the
input socket that they were trying to "repair"
With clean ch controls at 1/2
and 14mV, 400Hz, at input and DSP board diconnected
IC1 pin 1 56mV , pin 7 360mV
IC3 , pin 7 40mV
TIP42/147 , 2x 047 ?, JE340
2x 270, 470, 0.2R
220, 1.5K, 3.3K, 10R 1/2W
Remove 4 heatsink screws and 2 pcb screws and DSP board
to release the preamp board
IC3 pins 6 and 7 to clean level pot
and IC1, pin 1 the trace to th eclean channel
For testing needs a ground connection to both
the pcb ground points, PS and signal or nasty noises.
Crate GFX 65, 1999
loose input side gnd sc, probably from owner loading down the i/p plug to
"cure" the problem which was at other end of board , the int/ext 1/4 in socket diverter soldering
Crate GLX65 combo of 2004
Uses miniature pots with clear plastic
shaft and illuminator bulb inside the pot.
Body 10x10x5 mm and even then space inside for a wire-ended bulb. The
spindle made of clear plastic to conduct the light into a knob with red
Anyone know of an independent source of these.
For future reference, as in for mechanically broken switch, all the pots are
fine. Only 4 years of normal use and yet again flimsey push/push switches
are falling apart. Replaced those with robust conventional toggle
switches, enough room after bending the pins,
wired across to the pcb, and only SPST use although
they are DPDT switches. The mute switch is of stronger style.
The compact LEDs illuminate the surrounds and the pot
bulbs illuminate th epips in the knobs.
3 screws at rear release the prea section from the rest.
Mark ribbons for orientation etc,
to relese ribbons push the clusure strip.
Reconnect cables before rejoining metalwork, double
check you don't have 2 wires entering one socket,
very easy with these lack of terminations.
DSP footswitch mono, solo/clean/rythym stereo 1/4 inch
Tx 55R// .9R,.9R
pa 0.2R, 2x 270, 2 x 0.47, 220 2W, 1.5K 3.3K 1W
TIP142 TIP147, 072,JE340
prea , foam cylinders go around stemmed LEDs
Tx 55// 1R , .9 , .9
lights 40.5V at switch
grey ribbon 3,2,2.5,3, .9,40,0
rhythm + dsp -41,0,11,.8
Crate GLX65 , PbF problems
Multilayer ceramic C1 at the i/p prone to piezo microphony noise
Mains primary for 240V Grey and white, 11.5R.
In line , not 2 or more separate primary windings, DC ohms to nearest 0.1
Labelled by me as A,B,C,D,E crossplot (message souce maybe equispaced font)
--- A B C D E
A --- 9.2 8.5 12.5 1.5
B 9.2 --- 0.6 3.6 7.6
C 8.5 0.6 --- 4.2 7.6
D 12.5 3.6 4.2 --- 11.1
E 1.5 7.6 7.6 11.1 ---
This is a single primary made for / in USA
for export so wasteful construction as only parts of winding are used for international
variants , not 2 separate primaries (with perhaps minor taps)
Loss of output
Pulling right side of front panel and hiss drops in level but pa hiss rremains.
Breakthrough of VCO ? at low level.
Most of the 1/4 inch sockets use switch function and poor solder points
Crate GT212 amp , 2005
Mains hum problems
speakers together present 3.2R
Second time I've come across this prea ground connected to casing and
separate pa ground connected to casing via standoffs to metalwork. Underside
of pcb large solder pad, upperside 2 pieces of tinned copper wire. The
underside solder seems to compress , maybe pcb as well, and then exceed the
give in the star washer and looses good grounding. This time prea end ,
previous time was pa end problem.
This time will solder brass washer on underside,each end, solder just
between washer and board , not standoff touching surface.
Declench the 2 nylon standoff and push out rearwards, last to reassemble
Replaced input socket , wired in, mechanically decoupled from pcb
2x TIP47,TIP complement
Mains antisurge ? TI? 155P UE1015 28R cold
072 ICs only
5W 4x .47, 2x 270 ,.1R
1W 1K5, 3K3,330,2x 10R
Triple footsw so bet 1 &2 goes to C/S/R on amp and 2/3 to reverb, mark
with stickers on amp and sw
Tr connection layout for 240V
Or Or W (1/4 turned) W W
8mV 400Hz in on clean ch with pots at 1/2, .58V over 8R load
over o/p device complement pairs
1.24V,36V,.16 // -1.02, -36V, .05V
+/-16 V opamp supplies
Crate Stealth GT-100H
trying with 70 percent mains , with a signal in just a buzz in sympathy with
vol and pitch of the input coming from the op tx.
sp imp sw out of posistion
Switchcraft EPS1 slide switch
4 amp rated and doubled up as used in Crate GT 100H Stealth output impedance
selector. Amp grumbling by buzzing in its op Tx and no output. The selector
sw had vibrated into the "off" position. Easy to get into and there is no
detent spring + ball or toggle flip-flop contorted torsion spring mechanism
. In fact the natural position of this switch is between the 2 states with
the moving contacts between the pairs of fixed contacts, ie off/ no
contacts, only the contacts themselves hold the slider in posistion when
manual moved. A huge slot that would take a carpenter's 3/8 inch screwdriver
but only requires a jeweller's screwdriver to shift, at 300 gm of force to
move one way and 600 gm the other.
Now I know what to do, just a 1/4 hour job to retrofit a dedent. Rob a
spring and ball from a standard slide sw. 2 grooves ground into the inside
of the fixed body of sw and hole drilled through the sliding section opened
out at one end for the ball , the end of the spring glued in place and ball
in-between static and sliding sections. Unclip an end to sliding section to get inside,
nothing will drop out or spring out.
this one now has a delatch force 600 gm one way and 800gm the other. As an
easier retrofit fudge perhaps a disc of rubber, sandwiched at either end by
the mounting screw, would bind the slider well enough to the chassis and
still allow movement
The ratings are embossed on the sw body but where the pins cme through, so
manufacturer must mark the chassis. For 110/240V selectable equipment only
used in the UK at 240V, I often insert a bent solder tag between such sw and
chassis at a mounting bolt, to lock into place. Too easy for a drunk
musician to change the sw trying to repair faulty kit.
But this use is for a relatively high speaker current slide switch rather
op tx 26.5 and 34.4R either side of red HT wire
Reverb tank both ends o/c, Accutronics 8BB21C1A.
Amp had been dropped as both Tx had bend bracket supports
pcb slots either side of the anode pins of the op bottle anodes
Unwound tape of the tank coils by pushing through with a small screwdriver.
The 27R was broken at the surface and simply rebuilt but the other broken at the core.
Unwound the output one , but it got knotted so no turns count.
But it did measure 198R and .06mm with micrometer
Former 4.3x 2.6, 6.8mm wide
turns maximum 7 x 10mm until touching the iron laminations.
all too small to set up on my coil winder so went back to hand-drill
with oddly 56 to 13 teeth gear ratio. Set the plastic former on the stem of a
pop rivet and mounted in the drill jaw.
Measured off 43m of .07mm wire and "skeined" onto a block of polystyrene so could rely
on airbreak as back torque, ie minimal. Bubbly cut edges of the block are ideal
for holding the fine wire without it slipping off.
After pushing a thin rod through the block and setting
in a small tube on a clamp. 510 x 56/13 turns so 2200 turns. Measured 261R so less length
and turns next time , just as well as with vinyl tape over the coil was touching the iron on reassembl;y.
This one with 1.58Vac over the 27R maximum output over the other coil was at
300 Hz and 24mV over 266R. Other way round 2.66V , 300Hz over 266R
gave 1.5mV over 27R
Running fingernails over the springs gave DVM ac 10 to 20mV over 266R and
4 to 5 mV over 27R
Crest Audio Pulse 2 1100 power amps, 1999
Owner has 5 of these and 3 have gone into protect mode, all the same
symptoms. All look the same but not sequential serial numbers. He's getting
someone technical to look at the speakers and leads and as they are used
from a diesel generator maybe a problem there. All failed in use , not
abuse, not failing at switch on , and no earlier odd noises before failing.
Anyway these 3 amps show clip LED on both ch, and then drop into protect.
I've looked inside one and all healthy appearance. SMPS fires
up enough to deliver about +/- 100V rails, both ch, for half a second , fans
ok and relays click over but then drops into protect. No excessive mains
current draw at any time.
This one and the others , both channel o/p measure about 13 to 15K to ground
and not tied to + or - rails so will assume PAs are ok at this stage and
maybe falsely going into protect.
Goes into protect mode at switch on.
Useful info and schema on these G class amps
as well as schema only, on e-service
One smps supplies both amps and 4 rails, each rail supplies both ch, I've
cut the "overdrive" rails temporarily and running on +/- 60V.
Output has about +18V on ch1 for about a second before dropping down to 0,
so o/p DCsense line to the PIC tells it to go into protect, of whole amp.
With 15R load then op jump is to about 10V. The other ch2 is fine , no more
than 0.5V on output loaded or not.
Same 2 (4 in full operation) rails supply both amps. All electrolytics check
out ok. Problem fault tracing is 3/4 of the active in this amp shows the
same 18V or so jump at power-up.
Disabling the protect line, so the amp powers up, shows nothing amiss after
2 seconds, on all main transistors, running at +/-25 V rails anyway. I will
repeat this now at +/-60 V but as no 1 to 1 correspondence of device
numbering or posistioning between ch1 and ch2 a bit awkward and I don't
expect to see any substantial DC differences as has settled down after the
first couple of seconds. How to zero-in to the problem device . Nothing
untoward at the pa input but I will tie to ground the next time of powering
up just to confirm.
Looks like all 4 off 1M , need replacing, all those matching operational
position of R182.
Has 80 V in normal use over 1/3W 1Meg and used in dampish conditions is
enough to make it go high or even o/c., not removed it yet. In an area of
circuit not easy to measure or even compare ch for ch. Hooking another 1M
across it is enough to give amp operation without disabling the DCsense
Its this R that takes the central biasing section low at power up before the
Tr25+C53 section becomes operational.
At least the schema are around. Some notes in passing, you have to be
careful how you pick up that large pcb , by the heatsinks and front
metalwork not by the edge or rear as those large piercings make it weak.
Discharging the rectified mains DC cap of course. Maybe all component
oles( certainly the 4 off 1Meg Rs) are the size for power transistor legs or
IC-pin eyelets so although plated through holes , minor components like 1/3W
Rs have a lot of solder around the leads so libility to cracking I would
Not actually the 1meg failed it was the TO92 over the complementary 1meg
gone 35uA leaky, pulling the zero point upwards
No screws to Speakons. Remove inner screws rear and under. Leave front panel and handle plate
in place. Undo bolt and nylock hidden under wiring cluster
Handle via the front plate , heatsinks and transformer at rear, not the pcb as large
piercings must make it weak.
Cable tie the output subboard in place to protect header pins.
Add XLR barrel to protect the exposed orange connectors
Add 470K over mains DC caps for self protection should you forget to discharge. As large and
unsurrounded board it is easy to drape solder over something. Knocked out TO220 device doing that
,leaving non working SG2525A , Vcc of 5.9V wrt livegnd, shutdown at 2.5V , Vref 4.3V
7.2V on ZD2 at standby.
TR48 pass tr TIP121 CE short , replaced, lift clip slide ptfe under clip before sliding along the
channel, in reverse pull and slide the clip over PTFE
With 1uF 630V caps on the 4 power rail cuts , 2 to 0V and others to appropriate points , not zero
There is no 1 to 1 correspondence of ch 1 to ch 2 TO220 chains on the h/s so marked
A to I on side 1 front to rear and 1 to 9 on side 2
Correspondence is then
1E,2F,3D,4A,5B,6C,7I,8H,9G but beware of face reversal
Placed 130V 20mA bulbs across the 4 breaks initially.
IV for intermediate rail volts and OD for overdrive volts
+/-IV very dim <>4mW
+/-OD bright <>10mA
soon drops into protect then short duration operate
+/-42V, +/-110Vwrt 0V
removed OD lamps
+16V , -27V IV rails
+/-15 V regs ok
TO220 voltages with the 130V lamps in place
1 to 9
Apprx .1amp mains draw at 240V
PIC protect line voltages in this situation
Current, -13.6 at R49
Error, 0.01V, R10/R13
Brownout 8.9V, R34
DCsense 4.6V, R21
-2.7V at R49, 0V at R13, 8.6V at R34, 3.7V initially at R32
(leaky TO92 problem)
Brownout signal for various mains
9.1V at 90%
7.3V at 80
5.7V at 75
4.5V at 75
3V at 70 &, 220V on BR2
Placed 24V, 250W halogen bulbs in place of 130V bulbs and gives
+/-60V IV rails
With extra 1M across R82 op DC goes to 27V
With extra 1M across R60 , 0.2V DC on o/p and amp goes into "operate"
2mV over R59 , 0mV over R58
50mV over R61,0 mV over R61
Replaced the leaky BF423 with joggle legged MPSA92
Rails reconnected at "SP" links and main rails are then
load test 0.23V , 400Hz in with mid set of vol gives 4.5V ac over 4R
Second 2x 1100 amp
19.1V on smps wrt live gnd
54V,-54V,-53,53V on MJ TO3 cans
Vaux (5) 42V operate
R49 to -13V
Sometimes will power up with CLIP1 LED on but will not pwer off
and 110V on rails
R173 goes to -12V
R73 goes to 1.2V then 0V
Burnt out R146 problems again in a TO92 device in a
, gone B-C-E shorted so more obvious a problem.
Crest Audio Pulse 2x 1100
op 2 ok , amp 1 comes on clip led on then drops out, no DC
on outputs. Burnt 470R R146, oc 56R R139 and TR37 &38 replaced with
MPSA42. IC5 broken , o/p on -rail
pin 5 i/p -ve at C93 and R158 at 0V
Crest Audio Pulse 2x 1100
R229, 100K at IC10-B
MT+ no longer divided to non-inv ip; divided -Gref1 to inv ip
so no window for the DC error , so falsely tripping,
gone oc in effect, due to solder failure, in an area of high capaditance so difficult to find
Crest Audio Pulse 2x 1100
fans just momentary flick
op 2 goes to negative rail V
stays in protect
Convinced myself, erroneously, that this time it was a ps or +/-15V lines issue
5V on R32
momentary low V on both + &-15 V lines at opamps (-4V and +9V or so)
+/- 40V or so on power Tr devices staying high for some time after protect mode
up to 22V on Vaux5 line at D31
3.9K Vaux5 to live gns DVM
18V on ZD8, and R180 for a second but Txdrive for only about 0.1sec
Shutdown 5.9V for same time
Soft start jumps to 1 /1.5V
Zd10 about 0.7V for .1sec
R166 to 25V
Vref holds at 5.1V for > 1 sec
15V zener over ZD10 stays on longer
V on C75 drops from 48V to 20V (beware of this 48V voltage present in working amp long after switch off )
V over R165 24V down to 4V
Thermal fuse between opto and R165 is inside the switching Tx
1K across TR47 to keep supply running enough to monitor and 17V pk-pk wrt op gnd, 12uS symmetrical peaks at D50/D55 so
both complementary drives working
810R between ZD9 and R180 to disable TR47. Cut the 4 HT and MT "link" points and
it was HT loading problem. Removed the 810R and zeroed in again to problems
around TR32/33 and TR35/36 overheating.
Beware multiple change of orientation etc between ch1 and ch2 and replacing BF422 with
twisted leg MPSA42 and BC450 instead of 2SA872 adds more confusion.
Added peg spring heatsinks , as per tips files, to these TO92 , requiring reemoving poly cap to
grind a slot on one. 70 deg C temps now down to 50 deg C
Directly in series R112 and R7 representative of the crazy R numbering are next to the speaker returns on the schematic
Protect line data taken again for this particular amp
R49 -13.5 to -12.6V
R34 8.94 to 9.01
also at diode D51 24.1V to 23.86V
0.083 400Hz in and 1.72V ac over 8R load with mid vol
With 2.07R high power load (2.8R plus 8R) , mid vol, .156V 400 Hz in , with both ch powered , 3.4V over 2.07R and 1.4amp
mains cuirrent draw
Crumar Roadrunner 2, 1979 , Italy, synthesiser
Chorus effect not functioning. One of the 5 CA 3094AE not functioning but low
level of output. Connected 6.8K between the chorus maximum level signal
at one of the CA3094 and other end to the board output. The F 4727 was
probably Fairchild 7 stage CMOS counter. ITT SAA1004 f divider. Mostek MK50240N
probably = Thompson MK50240 top octave generator.
If one key sounds but repeat depression does not then due to
mis-alignment of contact spring. Un played the spring must touch
the long contact rod common to all the keys to discharge
or it will not play when depressed.
Crumar Roadracer, RRC, 1978
One note per octave absent.
Its a frequency divider , 7 stages , broken into a few isolated stages but
in this use they are chained together so 1 4024 would do and perhaps 1 +
1/6 4049 for buffering.
The trouble is the original uses 2 supplies -15V for outputs buffer supply
and -27V for the logic.
Buffered trannie input and
running the CMOS 'upside down' between 0 and -15V ?
Found an exact replacement so didn't bother fudging
pinout in D.A.T.A 1982 digital
along with AY-1-1320 and AY-1-0212T, MM5891 adjusted pinning
may be useable there.
Two keys were sticky. Not due to rusty pivot but under
each key is a standoff carying a shaped rubber piece
to stop keys swaying. Presumably going sticky , replaced
each with a piece of 0.19 inch silicone sleeving minus
cores. Perhaps squirting talcum powder under each key
as maintainence may help. Gain access to underside of key
by opening out the metal channel at the rear to release
one pair of nibs on the white pivot plastic which allows
to slide off the remaining 2 nibs. Slide the key to release
from the hidden constraints but still stay captive by the
thin and vulnerable switch contact.
A nail wire staple hammered into the casing to keep the
top switch plate away from the leftmost key.
Custom Sound 2005, Mosfet amp, made 1988
Volume faded down after about 1/2 hour .
No tranny/diode thermal monitoring of the heatsink and no FET for gain
control in the pa or FET in the preamp , all 4558 opamps.
No obvious over-heating or solder problems on any of the boards or flaky
Springline reverb throughput had failed due to corrosion
on one of the springline phono connectors.
This Accutronics springline was 200 ohm for in and out
Dummy loaded (4 ohm and 6V ac) took the heatsink up to 70 degrees C and held that power
level for 40 minutes with little variation in preamp output, pa o/p or DC
rails so a matter of the usual treatments for the numerous IDC
interconnects, sprung IC sockets and 1/4 inputs, despite no response to
twizzle stick and reported fade.
Dealt with all interconnects (stagger-marginally-bent
the pins and cleaned to give better holding), IC /IC sockets and
beefed up all 1/4 socket connections
as 5 channel all in a row, by running
silicone rubber cord the length over the sockets
with Hama/Perler/Pearler beads 2 over each contact, fed onto
pired up cord as in threading a sewing needle.
Pairs of holes drilled through the pcb to
take wire loops and a Hama on each
to tension down the cord between each socket.
Then hot-melt at the ends the down-pulls
and the twisted ends of the wired tensioners.
The mains fuse cap was exposed to a screwdriver
2x 2SJ50 and 2x 2SK135
bf470, 2x BF469,2x BF423, 1K,
2x 1K, 7x 4558 on preamp
Custom Sound Colt 10 combo amp
Intermitent o/p like a bad i/p socket.
Dry joint on resistor at i/p.
Another dozen or so leads had holes on one side of the solder joint.
It looked as though the lead cutter plate after assembly was blunt and
pushed all leads over before cutting and it had taken 10 years for
this stressing to open up as dry joints.
David Eden "The Metro" Bass Amp,600W , 2000, 50 Kg
Cut out in use then came back.
Next time of use, failed to give output but owner noticed clip light in pre-amp functioned as normal
Now I have it, I cannot induce it to fail.
Likely suspects the discrete wire IDC connectors for power and signal
interconnects, unsupported wire-wounds on end, mains thermal switch.
I did not like the front panel switch in line with the speaker line.
In standby instead of cutting/shorting the main amp input you switch out the
speaker. IDC interconnects on the speaker lines and power lines seem a bit
irregular to me but as cut out rather than distortion those power lines
Speaker units check out ok.
The function of the 12V, 10 W "festoon " bulb in the
variable crossover in the cab is a fuse.
Speaker switch rated 3amp and thats for AC, could easily be the problem, let alone potentially "fatal" to the amp. The cab wiring and pair of 4 ohm speakers in series seem fine.
It would not take much fumbling in poor light, drunkeness, confussion or
whatever to flip that switch in full use , its not recessed and in the back
of the cab. The other 2 paralleled outlets are not
switched, but I may hardwire/solder back to the pa.
Found another nasty under the ps board but don't think it is the main
This pair of wires to the speaker switch had one of the wires squashed
between a large W/W ceramic cased dropper under the ps and the chassis.
Cut some high temperature silicone cable sheathing into a spiral,
wrapped around the replacement wires and put cable ties
to each end to.
Original wires melted through but as it cuts the earth to the speaker, presumably no problem
as such and wire not broken, just failure to sometimes switch out the speaker. But there is smoke blackening or something
grimy in that area but it could be a small electrolytic parallel to the fan
cooked as it is directly over the large droppers and leaked electrolyte but
all rather nasty. The aluminium of the chassis directly under this
particular dropper has a strange flecked grey corrosion or something that
probably more likely due to electrolyte rather than vapours off the charred
The corrosion i've photoed here
The overexposed T area is the mains transformer and the groove marked "<"
was created by the squashed/trapped cable or exposed wire core probably
From "<" to T only about 10mm so just 5 mm or so free gap to run these 2
speaker wires between mains torroid and high temp wire-wound dropper with no
added high temperature sleeving.
The grey flecking is what I'm assuming is electrolyte corrosion effect
rather than burnt PVC product.
If this fan lytic over the fan supply dropper leaked to short in use then
dropper would generate more heat as well so compounding as well as shorting
out the fan to the main amp heatsink. The owner had used the speaker switch
in the past, during sound checks.
The protection circuit is activating before the 60 degree centigrade
fan switch is cutting in, under high load.
The fan switch temperature , testing in isolation , is about right.
The big triac on the mains, crowbar operation to
blow the mains fuse if too much mains power drawn presumably, 60K to neon for UK and about 22 ohm in line between triac and switch.
I've photoed the tracks and components and determined the schematic of this
Hard-wired the 2 lines from amp to speaker outlet , there were 12 chances of a break in that route, to and return.
3 pairs of IDC and pin connections in each line.
Using dummy load the thermal protection circuit was
activating before the fan thermal switch.
Monitoring the line from pa to ps with the LED
thats on if all is well.
The voltage changes as heat builds up from
about -13.5V down to about 12.7V when it
switches to about -0.3V , LED goes out
and pa is killed. It was the LED on the ps
that was failing. This LED passes current to the
start-up hold-off circuit as well as turning off
PA if the fan voltage fails genuinly or falsely.
This LED also on over the high power droppers, replaced
this LED off the board as well.
If I'd thoutght about it I would have added
a second board off the ps , bolted to the chassis
with these 2 offending high power droppers on it away from
the ps board. Bad design slinging them under the ps with
active components over (heat rises).
Added a 40 degree C
switch in parallel to the existing Asahi US-602S , 60 C one
but resets at about 25 degrees C.
If one switch fails there is still the other.
Replaced the MPS8599 with a BC212 rotated 180 degrees
to pin match , in case the original was suspoect due
to excessive heating if the fan had been stopped.
Before pushing into the heatsink, check temperature
controlled function of reducing gain to zero by a metal
funnel leakily connected to a low setting of hot air
gun and piece of heatshrink tubing on the small end of funnel.
ps main voltages +/-78V dc.
fan supply w/w dropper 75 R , 100R for preamp
pa uses 10K, 2.7K, 3.9K, 4.7, .39, 150R
2SC3858, 2SA1643, 2SA1494, 2SC4327, MPSA43,
MPSA92, J112A, MPS8599
Heat output measurements on 400Hz continuous sine i/p.
Into 4 ohm load with room temp 19 degrees C,
for 25W o/p in load, fan outlet temp 25 degree C
for 52W , 30 degree C at fan outlet
David Eden WT800, 2010.
Blows mains fuse an hour into a set. Then over the weeks blew replacements every now and then.
Blown ones not retasined but owner reported they were black stained.
Sometimes after 1.5 hours originally , now sometimes soon after switch on ,
sometimes a bit later.
Amp plate says 5A(T) for 240V use. Inside the IEC, is one non-blown 2A(T) in
the active position, ah! the simplest of repair jobs, BUT
No reported noises like magnetisation buzz or speaker noises , no smoke or
smells. Owner uses the same cab and speaker wire with another amp ok.
No blown fuses retained by the owner but reported to be blackened. 2A fuses
passing 3A or so and then failing when asked to pass 4A say, but they will
have fuse-wire breaks , not vaporisation and blackening.
Tx torroid 0.8R or so per primary , measured cold, seems reasonable for
135mm diameter, 65mm high Tx. Not in a position to check the main caps yet ,
but no bulges.
Any Eden usual suspects? PbF and RoHS stickers a-plenty
As found , a 2 amp fuse in there in good condition , not blown because the
triac Q6025 has failed, so front lamp for live mains but does not turn on via the switch
alternistor "600 volt" site:co.uk
throws up no UK suppliers for 600V alternistors
luckily no one ever uses a snubber in this use, usually just a triac, so
replaced with an ordinary 600V triac and turns on and off ok, presumably
maker had a stock of alternistors , so used them instead of a triac there
Digikey seemed to list alternistors but not 600V ones.
The failed one has no T1-gate resistance in the 10s to low hundreds of ohms,
is that a (sometimes) characteristic of alternistors ? otherwise no gas
venting through the epoxy fill or other signs of distress
800 watt toroidal transformer operating at say 400 watts. Secondaries lead
to conventional bridge rectifier and smoothing caps for +/- rails. A break
appears in the DC rails central 0V return to the transformer, could that
lead to a blown mains fuse, via inductive action?
The power amps always survive . In the process of exploring suspect caps etc
and turning over the pcb, the spade-connector for this 0V connection came
off the pcb spade. Looking under x30 on the spade and what I can see of the
line spade-socket, I can see no sputtering or smoke trails or anything
suggestive of a problem there.
I'm aware that a valve output matching transformer working hard and there is
a break in the speaker wire/connection /voice coil then enough voltage can
be induced in the primary side to knock out the output valves and weld turns
on the primary. But I do not know if similar in a mains transformer would
give enough current , from the energy stored in the inductance , to throw
back enough current , at over the mains voltage , to knock out the mains
This amp has an inrush limiter, the heatshrink over
it looks fine. I don't know if a VDR variant or what but if it is the usual
NTC thermistor then its cold resistance of 0.6 ohms looks suspiciously low.
I'll have to strip off the heatshrink and try and find some numbers and data
Inrush limiter marked with logo something like 8 in a half circle
VEI or UEI , 20SP, 0R7
Having difficulty finding data on this but cold 0R7 agrees.
In 240V land I usually find inrush limiters of cold value about 3 ohms. I'm
wondering if as its a USA made amp then these limiters are used for all
models and its not really high enough cold value for reliable 240V use. I'm
thinking of odd magnetic domains building up in the core of torroids and
occassionally reinforcing the inrush combined with an initially only
marginal rating for 240V use. marked 20SP UEI, looking like VEI
looks as though its N20SP007 on
looks too low a value of cold resistance for all eventualities 240V inrush
Its a bit much to see that UEI logo of an egg cup with a variant of the ON
symbol inside instead of an egg, as the poor legibility 8 in a half circle
here, on a roughish surface, but I'll accept it as so.
6 amp rating for the international model, internal wiring set for USA is the
correct component, for UK 3 amp is fine but I suspect the cold 0R7 is just
too low. I'll replace with a higher initial ohmage NTC, 6 ohm cold, 2 in parallel for the current rating.
Tx .8/.8R / 1.8R 135mm diam,x63mm
Removed the physical left hand amp , leave earth bond bolt in place
Earth wire crimp for the DI board fell out also
Replace 1 each , speakon screws so you cannot hot test with the rear plates touching the solder points
Marked 10,000uF , 100V caps 1 to 6
To remove the caps, start with hot air gun under one set of 3 to break glue bonds and solder
as double sided wide traces also. Then use 100W soldering iron to remove those 3
and the other 3 then just need the 100W. Obvious weeping of electrolyte under
5 of the 6 caps, 1 had a couple of drops, but no sign of leakage onto the pcb, but assumed
at least one cap has failed at high temp and self-healed
Blackened pcb under R10 and R11 discoloured bands but reading 3R3 each ,pcb
charring >30M DVM probing and goes from 20V Tx secondary to 1000uF 10V cap
so unlikely a mains fuse KO
Anodes of the valve go via ok MPSA92 to the ps , but may replace the 2x 160V
10uF caps in that area.
Just leaves the 2x paralleled 3 , main caps 100V 10000uF. Other than
separating and heating and measuring ESR (not necessarily related to
self-curing internal flash-over) , nothing else left to explore?
If its recovering interlayer discharge inside the Tx then can't do anything
about that, any sort of tell-tale for that scenario? presumably add fuses
would 10 amp blow before the 5A mains fuse with failing electro?) to the
power rail secondaries
Heavy engineering job as a solid block of snap-in 6 Jamicon , 85 deg C,
LS, 809K(M) 100V 10,000uF.
Presumably failing because the contact verticals between are filled with
filled silicone rubber and hotmelt glue in the 2 central gaps and 85 deg C
someone's internal view of similar amp
1500W hot air gun to break the solder and binding of the most amenable set
of Cs for wedges under then completed with a 100W soldering iron : 4oz board
, wide traces and both sides of the pcb.
No oily messes on the pcb but only one cap end is dry, 4 have an oily film
and one has that plus drops.
Expensive set of replacement 105deg C ones plus try and get some through
ventilation, perhaps the replacements set at an angle to form a sort of duct
and a small fan or as in line with the amp fan perhaps a duct only . And
hope not an on-going internal Tx problem
Cold ESR of each is good and warmed to whatever a minute of low setting hot
air gun gets them to , no noticeable ESR change.
I suppose the only test would be a current limited 100V supply , resistor
and voltmeter to monitor implied leakage current and heating each cap .
Cooked all 6 at 85 deg C, with thermometer in the middle of the block, for
at least 30min and then applied 110 volt DC to each in turn, all charged up
and held for 30 seconds or so and discharged normally and equally, while
still at 85 deg C.
But not too pleasant electrolyte smell in the room. Orientation of the caps
was up the other way from useage and no vibration. I wanted one to show some
Removing ps board , remember the 2x voltage regulator screws
R10 and R11 are in fan control , overhearted to loss of band colours,
measure 3.3R each, slung one replacement undedr the pcb.
Blacking of associated pcb material , >30M DVM-R
PA p/n 10150, rev C
3x A1492,3x C3856, TIP42C ,TIP41C, KSE350, KSE340
6x .45R 5W, 2x 75W
soldered th sw N/C
spade terminalsed th sw N/O
N/O one thermal switch was KSD301 K050 PN so 50 deg C to switch on fan, logo lightning
stroke in brackets
Both 10A speaker fuses ok
VRs 7815A & 7915A ok
valve anode pins connected 1 &6, line to Q1 MPSA42
R5 390K to orange wire of P3 and J3 to C10 10uF,160V on ps
Beware with no PA connected HV retained on the 10000uF caps for a long time
Grubby patch of blank pcb material under top cover is a fudge to avoid
something on the top pushing down to cause a magnetic short to the Tx coachbolt. The mark
is just from physical touching of the thread, not from electrical discharge.
Removed coach bolt and no nasty smells or black streaks inside the Tx cavity. also
no awkward smells inside the amp , on first opening. Unlikely repeated mains fuse failure,
but both PAs stay functioning , due to internal problem in the Tx but could be a first, always
found to have welded shorted turns rather than intermittant shorts.
After removing main caps, clean and straighten the "snap-in" offsets of the pins.
Ball mill back rings around the 0V pcb traces top and bottom. Cut some 3mm thick
paxolin to glue over this central area to give a cant to the caps when replaced.
The 63V, 2200uF cap nearest them needs desoldering and canting over as well to
clear one of the big caps when it is canted over
P2, single wire to physical LH amp only . RH amp at the ps has on its conn
a trace of insulation for the corresponding wire but no wire. Fully tighten Tx only
after refitting RH amp as only just enough clearance space.
2 pieces of nylon cable ties pushed into the gripper tangs of the mains sw.
Triac gate has 4mm tag/spade.
Replaced triac with ST make BTA40-600BC, no change to 22R etc required
Refixing amps,fit the isolated single pillar first and then the 2 h/s sc.
Tried out 1 pair of main caps only resoldered in , initially
Green front LED on and red ps LED on
+/-76V on main rails for full mains V
101V ac on thin red/orange lead
T13 , 20V Y wrt Gn T12
Because of the nasty rats nest of wiring between fan (blows inward) and the ps caps decided
the only option was t add a small fan in the only bit of available chassis space, near the valve and L amp. Pilot hole and then
1.5 inch Qmax hole cut and 2 mounting holes and some expanded mesh cover and a couple of washers to
add space between mesh and active part of the small fan.
Removed those 2 caps and refixed all 6 with 6x 20mm fuse holders fitted under to 0V also 1 1.6A fuse
in the 100V wire , heatshrinked over and 1 x 3A in each 20V wire.
Hopefully will indicate which cap is failing , if continues to do so , even when running cooler,
at least should not knock out the mains fuse, just some hum or distortion from 3+2 main caps
DC at main ps conns from J1 to J4 J3 J2 , no fan on
134V and 135.5 V over R7
DEcided vibration , plus the overheating caps may have contributed to internal cap shorting
Looks as though the 4x sticky pads had been removed from under the chassis. Added tap washers , 1
under each of the most appropriate sc under the chassis. With a ball mill ground out a recess to seat the head of the
existing sc without protrusion.
Usual UNF/UNC / UK problem, just about could use the existing sc if the captive star washer was removed.
Cremmel and .5mm disc to grind a slot in the washer (and a bit of the head and shank thread but ok)
to break off the star.
If cable bunches are set between caps and Tx then perhaps no ned for
an extra fan. If no valve in place then a mysterious deep rumble /rustle
like wind noise
Dunlop Cry Baby GCB 95
Owner lost the original broken switch and of course
did not note the wiring.
Deduced wiring on DPDT switch
Blue / Blue wire to pot
Purple / Green (commons)
o link o
Needs a long stem footswitch. With this one with what looked like the original felt pad ,
11.5mm between top of sw button and top on internal back nut
eg Alpha L , 8D1 is too short.
Never mount one of these footswitches without the rear backnut
as any force bearing on the flat body of the switch will
break the weak brass nibs between the two parts.
If too short , glue a 3/4 inch diam, 1/4 inch
thick tap washer to the original felt pad and
take up on the back nut.
As a rough gauge to correct posistioning. To change switch state requires both hands
around the unit to compress the pad + sw. Roughly equaivsalent to deliberate but not
excessive foot pressure.
Dunlop Cry Baby GCB 95 ,wah wah,2005
From a wah-wah pedal only 2 years old so I don't see the point of replacing
with more of the same, as these symptoms are very common.
Poor bypass function and now total failure to switch between on and off
Both 1.8mm x (11 down to 10mm swaged )stainless steel rivets ground off to
separate the halves,push-push latching switch
Unless anyone knows differently then I suspect the poor bypass contact is
due to the interior packed with non-conductive grease.
Carling, Mexico is the make of this one , single pole c/o, silver plated
contacts and dumb-bell that can just about be seen in the centre of the top
image,then a locating cup, then compression spring, then brass cup that
seats the end of the swinging arm marked L in the next images. The dumbbell
jumps the 2 contacts at the top of the image and runs along the continuous
lower one, enlarged in 4th image, 5th is the swing arm magnified.
some background on Carling switches
Featured Article :: A comparison of boost pedals :: by Ken Nossardi
I think I agree with the comment in the quote about machine tool wear.
I've not removed the rivet that holds the ratchet mechanism - maybe shown on
a patent site somewhere. I suspect that ratchet mechanism, produced by worn
dies, is just enough to bring that swing lever over to just over half-way
when tested off the production line.
With, now, no reserve for in-use wear.
Cleaned the silicone grease out as not used for mains switching here, otherwise 1A 250V / 3A
125V rating. Why silver plating and then non-conductive grease in low
current/ low voltage use ?
There must be a "ball point pen" type latch action in the bush part so the
down action pushes the L arm one way then the other on the next down stroke,
with a click of its action on each upstroke.
plenty of spring in the ompression spring between dumbell and brass cup, so
no lack of contact closure pressure , leading to the bypass problem
Presumably due to wear the underside of the button eventually bottoms
against the end of the threaded part marked V, when L is only half way
across. It needs to go a bit further than half for L to swing across, via
the dumbell/cup spring sub-component action , to the other side.
Slightly tightened a small Jubilee clip around the threaded bush, as a
guide, and hacksawed off about 2mm at the V position, not apparent in these
images, so can be quite neat.
Stuffed more plain silicone grease in the ratchet section
No matter, in this case (not mains use), may replace the rivets with
Spanish windlass "E string" wire over 2 small soldertag rings and locked in place. Anyone know
of a source of such small diameter /long rivets for other occassions?
Of course just fixing the lack of switching does not require removing the
rivets. In the end just used 2 small eyelets in the metal to locate under
the back nut , 2 cable ties around and one across to remake.
If there is non-conductive grease in other , otherwise 240V rated switches,
then that could be a generic problem with all switch makes, used for low V,
low A purposes.
Missing feet requires UNC screw. Missing battery cover see tips files.
Dynacord Powermate 600 mixer amp , 2006
Supposed to have only a minor problem for repair but there is obviously
(also) a totally black shapeless lump , presumably remnants of a burnt out
capacitor. Marked C17 between F1 and F2 low power rail AC fuses. Anyone know
its value? probably about 1nF, too low a voltage rating? or because it lies
over a power rail track between D17 and C7, coating burnt off. Loads of
these mustard yellow globular Cs around the board
The output relays seem to present a short to the speakers in powered off
mode, have not got to the solder side of the board yet to explore.
RoHS construction, of course may present other nasties when I get there, not
The muting TO92 J111 FET is
falsely pulling down the signal line, -18V control V on gate dropper of both
channels but not so the gates.
Not the FET but the gate to ground cap going ohmic, see more relevant
exporation on one of my tips files and item on WEEE/RoHS/PbF
Mono operation secretly
selected rather than stereo/2 channel operation. ? Both channel signals get to
the mixer output jacks and the mixer ribbon is remade with both channel
lines intact but there is a break in one throughput before the ribbon, but
punch-in 1/4 socket bypass contacts are ok.
I was being mislead by L & R on the overlay near the mixer/PA umbilical
ribbon CN1. L is the L ch and R is the quasi ground for the L ch, the R ch
comes in nowhere near it. Full signal L and R gets to the PA but only very
low level gets to the R ch PA pre-driver stage, in for some messy opampish
fault finding or false mute, if the power rails are ok.
I've not seem them before, no name on
the exposed parts of the connector. 0.1 inch pitch ribbon maker ?.
views of connectors , same, both ends of the ribbon for photoing
convenience. top as found, pcb part, ribbon part internals
Black end pieces are just locators and for polarising,different
sizes/recesses, not gripping the white bits. Locking is done internally
somehow. Anyone know the professional way of unmaking these connectors? you
do not umake the second IDC connection, per pin, in the process of
I ended up using a knife blade and then jeweller's screwdriver to get
purchase between pcb and white part that goes down to pcb level, lacquer
damage can be seen in middle view. A dentists sickle probe as a
lever into the small holes along the white part edge levers it off.
4x MJ15004G, 4x MJ15003G
4x 4r7, 4x .22R, MJ15031G, C4793, MJ15030G
MJE350G,MJE340G, BD241B, 2x LM317J, LM340T5
1K CN18, to CN8 ,55R
CNS1 has +/- 15V, 24,51
F1 , F2, 40V ac
+/-69V dc rails
L bias signal ok
fan blows outwards
Rch mute, J111 Q303 preceeding opamp
OP301A pin 1
L ch, J11, Q103, opamp 101B, pin 7
LM317 +16, -25
The J111 , falsely mute
reads -18V, -1.1V and proper operation -18V, -17.6V
0.1uF/100V MLCC gone ohmic. Putting a DVM/ohms
over this showed wavering 20K to 30K , same when
.125V 400Hz, 40dB gain, 0db slider ch1,
0db on master 0db on bar meter, 0.8V on l/r trace at CN1 main board
1/4 in jack in Main Output , L 0 ohm to L at CN1
Ribbon (L) 9 to mixer out
CN(4) sig (L) H1 SIL pin 4
CN(9) Sig (R) pin 2 of SIL H3
Saw the owner 6 months later and no further problem caps
or at least enough to cause noticeable problem.
Dynamix Stage 250 (plus suffix ?), 1984 mixer amp
Intermittant loss of one "tape" input channel
Retaining bolts hidden under the feet.
There are switches at the phono inputs
and replaced them with unswitched ones.
Uses 10R 10p16 , 10N16
4560D, 7915, 7815
springline 75R, 40R
Intermittant drop out or relay and loss of o/p
Bad umbilical IDC connection on the relay board branch off.
Moulded or invisible closure of the black IDC sockets.
Ball milled alternate sides , cut into with scalpel and thin nose to bare
wire and IDC blade, flux and soldered. All 6 connections of the last 2 connectors.
Failure of a + or - 15V to one of the prea channels would just mean loss of one ch
not total amp loss of o/p.
Did not cure the problem , cut out IDC and header, soldered the wires to the pcb.
Cause unknown as opened up the socket and plenty of spring on the contacts and
continuity of solder over idc seemed fine.
Makers probly did same on one of the signal IDC connectors , soldering to the header
As on a board where the pots did not match separation spacing on the front panel ,
replacement ones would not have different spacing.
the 100uF is not the relay timed off timing cap
the 2 V reg h/s were too close together, bend back vanes
Only half the relay used for o/p line, green flash and bang in speaker so heavy DC .
pa checked out ok, due to bad crimp connection on -ve side of main bridge rect.
Also bad crimps on IUC and mains fuseway.
Another time intermittant loss of o/p FX level pot ground bad.
On relay board 100uF is not a timed off cap.
Black .1 inch Harwin type IDC connectors are bad contact somewhere.
Makers had done away with one at manufacture, soldering to the header pins.
As front panel spacing does not match the underlying board , and splurged pots
pins then a bodge job at making.
Soldered the first 2 ribbon connectors to the boards as loss of power rails
there leads to relay dropping out. Problems on the others would just lead
to loss of one ch.
Only one set of contacts used on the relay. Excessive green flash on
contacts at dropping out due to bad crimp terminals on one of the main DC lines.
Bad crimp contacts on IEC and fuseway. 7R NTC on mains line
Electro Voice M/C 150 microphone
Dead mike.Broken wire at the switch.To access unscrew the dome,desolder
the wires to the active part. Remove XLR housing and then the 2
screws holding the switch to the body.
Came bouncing back a few months later. It
was now obvious the problem with these is the transverse
pin bends. If the gust is held in place while
the end of the pin is ground off and extracted
and a replacement one made , then that would
be the solution.
Electrovoice EV Sx 300
dropped and measured 25R , soft tap on side and down to 13R
Dart point in spades to remove
mark leeads before removing but worst ones were to the speakons
bass 4.3R, horn 4.8R
to remove horn , remove 2x 5 recessed bolts on rear and 2x2 seemingly "blocked" off ones, removed from the front
main coil 0.9R, other one 0.6R
1.15uF, 160V ac
removed speakon spades and soldered in [place and restresses other spades
5.2R overall at input
Electro Voice Sx 300 speaker
Bass driver giving off a noise like frying bacon of fairly constant level
compared to varying audio level. They had used epoxy glue and soft contact
glue at 2 different stages of fixing the spider to the frame. Epoxy had
squeeged into the interior forming beads of solid epoxy up to about 10 mm
long by about 2mm that had later broken off and was rattling inside. So
gummy/soft glues only is the lesson . As there is always bits of sub-mm
aluminium oxide etc , but greater than air filter mesh size , inside
speakers, that don't seem to make any humanly observed rattling
interference noises , anyone any idea what is the size that becomes
intrusive ?. In the core that is , not staples etc on the outside. RoHS
stickers all over and all sorts of other problems in the cab but not PbF
isssues (this year)
These bits were rattling around in the interior space not passing through
the air filter gauze or getting graunched in the vc gap. Demounted spicer
and cone and for "reconing" this one I used 3 slivers of credit card, hardly
thou/mil sorts of dimensions.
You need a jam fit, to coin a term. Not a clearance or sliding fit as you
need the cone to stay at a pushed in distance, say 5mm below natural level.
To allow the glue to have a closing pressure that is a once only application
of force. Not removing hands and then placing a weight inside the cone. So
the circular VC former goes slightly triangular with 3 credit card slivers
or slightly squared with 4 (excessive deformation/ holding force for this
The precision required for a shim cylinder (even with an axial gap) for
coning/reconing would be near impossible to have a "jam fit"
This one given a work out with high power 50 hz and now back with the owner.
Does not bode well with its fellow, 5 problems with this one. Loose horn,
loose spade connector, another one the wire came out of the "crimp" on
normal handling, spider of the bass unit partially unglued from basket and
these bits of black epoxy rattling around inside (now in my black museum)
Removed epoxy coatings with dremmel and grind disc, also abraided the spider laquer
covering for better key to contact adhesive.
Cut into periphery of dome for jam fit spacers. Before realising had to remove cone and spider- thinking just regluing the
free part of the spider and clearing out loose epoxy. Cut a piec of hot melt glue stick , knotched at the ends
to lodge on dome remnant then dowel with a large grommet at each end over the speaker mounting
rim and rubber cord between the 2 rods to pull the cone away leaving inspection and gluing gap
at the spider.
Ev bass 812328306293
Ev horn DH3 8033099006296m
Horn loose rear and internal screws , use cutdown ratchet spanner and hex bit to undo if not
taking the 2 halves of the cab apart or slackened a bit. Wire to horn dropped out of a crimp
on moving the wire
Part remove cabinet screws on top half to allow removing horn. Remove rear screw before parting the cab halves.
Intermittant speakon spade connector
2 unmarked festoon lamps under crossover pcb , powering from 3V and 1amp , after 1 sec glowed orange
.5R cold and 1.1R across xover to T
Elka organ /AY1-5051 replacement
From usenet discussion, placed here for clarity
AY1-5051 Fixed Modulus
Divider chip? It was made by General
Instruments (later Arizona Microchip) and is a PMOS technology.
a couple of salvaged 1978 , AY1 5050 in front of me with pinning, no
knowledge if working order.
With a DVM diode test and -ve to ground pin
one measures .71 to Vgg and .66 to Vdd pin
other is .8 and .74V
for isolated dividers with no internal linking and a few readings referred
to pin 1 as -ve
to pin labelled input .88 and its o/p .78 and some others
.95 i/p and .86 o/p
,97 and .85V o/p
those with internal linking are nearer the o/p readings, up and down
+ probe to pin 1 ground then no forward drop reading to any other pin
, max 2V IIRC on Fluke 77
Early Maplin in UK catalogues had pinning etc for a number of AY1- organ use
Tackling a functional replacement
Wire a chopped down to 10 pin turned pin socket to the pcb and glue in
Another chopped down socket , to plug into the first, wired to a piece of
Try an "upside down" ,positive ground (is that possible?) CMOS divider between Vdd
and ground and voltage divided input signal to one of the CMOS inputs and
and try just one output , level shifted with transistor and a couple of Rs ,
from Vgg, to drive any high level tone generators or whatever comes after.
Power supply. You have to use the -27 volt VGG since VDD can be
modulated. So a 12 volt or thereabouts zener, and a series resistor
should be ok to get a -12 volt supply. Which will feed some CD4000
family chips, running upside down. Their positive power supply being
the PMOS ground. Typical drain for the old chip is 3 milliamps, that
should be plenty for a handful of CMOS logic running at audio frequencies.
For each input, an input resistor, diode clamps to the CMOS power positive
(gnd) and negative supply, and a schmitt trigger buffer or inverter.
CD40106? Then use either D latches (4013) or JK ff's (4027) for the
dividers. Easier to get the short divider chains than the CD4024 if
you don't know how the external circuit is wired. If which edge is the
trigger matters, you may needed to chain one of the spare 40106 inverters
to get the right polarity to feed the flip flop.
For each output, a small p channel MOSFET, source to (PMOS) ground,
with a 6.2k ohm drain resistor to VDD. (Or maybe a jellybean PNP with a
base resistor. Depends on the sound that results, perhaps). You might
need a capacitor or RC filter across the output to slow down the edges.- Mark Zenier
E-MU 1616 digital audio system
Failed 48V ,.375A smps , TE18 on pcb
Only 6.8V output
1206 footprint inside a Chinese in-line smps. Amber colour showing an
underlying zigzag track like pcb trace inductor and a tiny fuzzy bit. In
series with 15K , only, and going between the coldside pre-rectifier hf ac
and the 48V dc output . Does not measure 0 ohm, not a fuse in that
situation. Overlay marked ED201 , ED = electrostatic discharge? Note, its on
the cold side. "surface mount" "spark gap" in goomages threw up nothing
Bad solder joint on the v reg should be the problem but just wanted to check
what this new-to-me device might be. Case cracked open in a vice painlessly,
2 clasps at lead ends.
looking under x30 it has a gold coloured if not gold plated surface with a
bit of ptrofiling, perhaps hiding another surface under as seems continuous
metalling from land to land, with a tiny brown dot in the middle and clear
plastic cover over
What a plonker. Now it is knocking out 48V DC, its function is obvious. It
would have been much more obvious if it was not at the edge of the board
with the L missing off the overlay designation ED201, and a more obvious
window in the casing.
I did discover that there are such things as SM gas discharge
Lid is "bottom" and undo both TO220 bolts to release pcb ( broke a trace
at the driver tr before realising the fixings issue)
Hotside C3866, 1.6A fuse, thermistor 1R,
peke diode, 33K
AZ431 AZ AE1, TO92 shunt reg failed , is it higher rating than
all the other 431 datasheets show?
Replaced .47uF ,50V as 75R ESR
Replaced with a TL431 and ps worked but there was 44V over the regulator, max 40V
in all the data I saw.
44V.0,2.5V wrt poer 0V
2.5V on either end of 220R
18K to 48V
Measuring DC over opto , R and op
for no load 1.11V,3.1V,47.6
500R load 1.02,1.41,47.3V
220R load 1.04, 1.09,47.1V
so functioning but as the original had failed I have to assume because
more than 40V, failed at switch on.
Eventually settled on adding 330K to the 18K and adding
1.8K to 1K to give 2.8K in line with the opto giving an output of 45.2V
no load 9.63V over 2.8K
4.41V with 500R load
External unit , unconnected to pc, Red "48V" LED and blue LED on ,
other LEDs show random display including clip LED ,but normal.
Just power-off click on phones monitoring
Owner does not use phantom , probably ok , but works ok with
now less stress ovver the regulator.
Engl E320, Thunder 50 reverb, 2002
Celestion V12-80 6.6R
reverb tank 1.1R, 220
tr 11 R, Bk 0.1, rd 37.9, gn 1.1, olive-r-olive 1.8-1.8
2 broken spring washers on the 3 pa bolts (windy drill toequing ?)
Remove 4 large bolts on o/p tr cover to release tr.
Remove 4 prea standoffs from chassis side.
Hold rear panel cover plate in with a looose 1/4 inch socket
Beware of flying LED and straining the grey ribbon flex solder ends so cracking.
Fix a bracket to the chassis captive nut for a vertical length of dexion and a strut
from that to the other chassis end captive nut to create a vertical support
frame for all the internal pcbs , to work on. Leave the bridging yellow and black wires and ribbons in place.
Angle to give clearance between 5881s and dexion.
Some long component leads not cropped
Even the maker's ECC83 retainers are
an awkward bodge-up, not even fully screening.
Place retainers over the valve pip then spring the tangs into the chassis slots
Owner has managed to get away with dragons teeth retaining clips digging
into the glass envelope of his replacement type with no bakelite base . How
to fabricate something approximating those woven glass mesh baskets that go
over the envelope and then a pair of springs down to the chassis or any
other ideas other than replacing with based envelope types ?
Incidently the first thing I did was undo the screws of the dragons teeth in
hope of relieving some of the teeth force before removing the valves , but
was that the correct approach?
I don't fancy making a pierced metal dome shape, that has to avoid the
fragile central area of the glass dome. So far I'm thinking of a length of
high temp glass sleeving knotted into a ring, slightly smaller than envelope
circumference, with a balancing "knot" on the other side. Then silicone
sleeving or springs and glass sleeving down to a pair of solder tags as
anchors. Nasty dragons teeth chips in the bottles but they survived.
Made up PTFE "jockstrap" as retainers, see tips files.
Another awkwardness of the Marshall ones is the tension points must be a
good inch below the bottle tops and part wrap around to avoid sliding off.
Yes underslung 2002 German Engl E320 50W combo.
First time I've come across one of these , to do anything you have to take
the whole amp to bits.
Bad centring between RCC valve sockets and the holes thru chassis
Epiphone Triggerman 100H : see Grainger
Euphonic Audio,amp 350,2001
Presumably a stock fault with these Euphonic Audio, USA amps.
If a problem not relating to the ribbon cables , before doing anything,
beef up the soldered ends of the ribbons with hot melt glue or the ends will fail
I'm having to
replace all 8 of the 1/4 inch jack sockets. 4 of the 8 are totally breaking
up inside. Assembly flaw - they used unreinforced plastic spacer rings on
the bush inside the chassis, not dense fibre washers. The ring breaks and
the bits drop away and owner tightens up the front nut, not realising that
without the spacer then the socket is skewed/levered against the pcb and
rear of front panel and the socket housing starts cracking up. Otherwise
sturdy but now detrimental soldering of the pins does not allow any give
there. The pins are joggle-formed to tightly fit double-belled eyelets and
soldered through the board so as solid as can be, with base of socket tight
to the pcb.
It seemed odd to see a 555 in there for just a hold-off timer function.
You need the same Ct/Rt values in both cases and one does not use a 555
The other pig with this amp , it uses that grey ribbon with soldered
stranded wire cores that can only take a limited number of bends/unbends at
the terminations before cracking.
4.7R, 38.2K,15R large Rs, NE555
2x 10N20, 2x 10P20 4x 0.1R, thermistor 2.7K in circuit cold
Transformer internal fuse 130 deg C
3.7R//gn 1.7R 16.2V, Y 0.9R 14V, or-or 0.6R 110V
Prea LM79L15, 78M15
9x 2072C, 3x 072C
Send / Return - 1?,2?, 3 gnd, ret line
i/p -13V supply
phones/tuner (maybe) -15V, Tu, G,G, o/p,+15V, phones
Event EZbus digital mixer not booting ,
LCD message says: "becoming EZbus..."
Dead as all functions controlled digitally, except for the display showing
This is someone else's broken one, posted out there and no response
"The power turns on and the green LED's next to the System and Audio buttons
flash for a second and then the LCD displays "becoming EZbus... It does not
advance from there. "
x5 visual inspection over
the main board shows nothing amiss. DC rail voltages agree with the
regulator types, reseated cable connectors.
No battery or F-cap found unless on the analogue board.
Start up is the same as that other one , I'd not noticed the 2 LEDs flashing
on for 1 second.
Changed 3 , 0.47uF caps of ESR 25 to 30R but system still hangs. Beyond
checking oscillation around each of the 3 crystals its then a matter of
seeing if there are data sheets for the main chips
I've downloaded the datasheets for the
controller, Cypress AN2131QC, and
24 Bit Audio DIgital Signal Processor, Motorola XCB56362PV100
so another download for the CPLD XC95144XL, nowhere near any crystal
leaving converter CS8420 and flash mem AT29C256 of the big chips
I did try powering up pressing
System + Audio (the LED flash up pair) while powering up , but no change
But I will try Play+Record mentioned as another make of digital mixer reset
before delving more into the hardware.
Any other button combination suggestions, nothing for EZbus found out there.
As nearly fully separated 3 lines of 28 control buttons I will try the small
subset of 378 combinations of adjascent pairs and the subset of adjascent
triplets of 3276, 3 button press combinations at power up, unfortunately
having to leave 10 seconds in between as longish 5s or so power-down/clear.
Then monitor the 3 clock lines to the CPLD and then try forcing the GSR
(Global Set Reset) pin
This other person's experience
"When connected to a PC computer via USB, the computer recognizes that a USB
device is found but cannot install it because it does not recognize what it
is. I went to the Event support site and downloaded the EZbusInstaller,
Firmware, ASIO update and XP update. Followed instructions to install the
Installer and that seemed to work, but when I try to run the Firmware it
does not recognize the unit and gets and error message that says no EZbus
connected. The Firmware instructions say that in order to run the file, the
unit has to be set so that the display is at the USB setting, by pressing
the System button and then the Next button several times. But it won't pass
the message that shows "becoming EZbus..." "
suggests that and this is a "pre-POST" problem but there is some variation
in LEDs lit on some button press combinations at power up , sometimes the
MIX LED lights on one pair of button presses , rather than the System+Audio
LEDs, as normal. Does this suggest a post-POST problem?
unlike from the EZbus FAQ having presumably gone past that and then hanging
at a blank screen but is initialising the USB function there.
I tried to update my EZbus firmware and, and now my EZbus LCD blank.
If for some reason the firmware updating process in interrupted (e.g., the
USB cable is accidentally removed, or you have a power failure), the EZbus
will not have the complete set of operating system instructions it needs to
function properly. The most obvious symptom of this condition is the blank
1) If you are using the latest EZbus driver, you simply need to
double-click on the firmware updater to reload the firmware into the EZbus.
Note that you may have to do this several times, power-cycling the EZbus
in-between each attempt, before the firmware will be successfully loaded.
This is normal, and is not an indication of any additional problem.
2) If you are not using the latest EZbus driver, download the zipped
file (below) for your operating system (Win XP or ME) to your computer's
desktop, or a folder of your choosing
WinXP Firmware zip:
WinME Firmware zip:
3) Unzip the file, again to either your desktop or a folder of your
4) Navigate to your computer's Device Manager and highlight USB Device.
Now go to Properties and click on Update Driver. Point the Update Wizard to
the desktop or to the folder into which you downloaded and unzipped the
files. At this point, Windows will reinstall the file EZbus.inf, which will
allow you to refresh the firmware, as in Step 1, above.
5) Once the EZbus.inf file has been installed, the listing within Device
Manager will now read EZbus-Needs Firmware Refresh, rather than USB Device.
At this point, follow the procedures outline in Step 1, above, until the
EZbus operating system is restored. "
Would it be worth trying to download firmware code and trying a USB link up?
going by the other person's experience, no point
2 and 3 button power-ups produced nothing.
for the CPLD / TQ100 pinning
CLK1 is 22.58125MHz
CLK2 is 23.99700 MHz
CLK3 is logic low
clocks presumably related sum and diff fashion with the crystals 22.579200
CLK3 , not from the USB chip, comes from VCO o/p of U3, a 74HCT4046 , whose
sig in comes from U29 an 04 inverter whose input comes from pin33 of the
CPLD functional blocks, which is firmly stuck logic H so vicious circle of
Incidently TP4 of 8 is the only one with any activity on , one of the approx
From the R&C of the 4046 CLK3 must be about 200KHz, I wonder what would
happen feeding 200KHz or so into the PLL ? something to try on next powering
U30 1.44,6.44 (i/p for 3.3V reg), 10.7
removed analogue board, rear board, same LCD message.
Unpluged LCD and replugged, blank screen , just backlight
If mains off for too short a time then Audio + System
LEDs do not light
Sometimes select M + Solo then MIX LED goes on
GSR L.H.L sequence
860R to 3.3V and GSR goes to .3V
Telephone number - the same number as it has been since 1988
but email is now the preferred method of contact so number deliberately not placed here.
I devote time each day to replying to emails.
(obscure/obsolete components,second hand test equipment,
Postal: 66 Ivy Rd, St Denys, Southampton, Hampshire, England , SO17 2JN
There is no point in contacting me about any of the above, the
repair job may have been done 15 years ago .
I cannot clarify or enlarge on any of the above.
A reserve email account is diverse9(commercial at)fastmail.fm.
Please make emails plain text only , no more than 5KByte or 500 words.
Anyone sending larger texts or attachments such as digital signatures, pictures etc will have
them automatically deleted on the server. I will be totally unaware of this - sorry, again
blame the spammers.
More hints & tips and repair briefs on