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, CDs and Radios, with some cross-over 
eg fault in radio section of a tuner-amp would be listed in radio section . 
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.



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 , N to Z 

Nady TD 1, guitar tube distortion effect pedal, 2004
Anyone else been here before ?
End of line , being sold without the power adaptor, presumably ran out
before the units sold out.
Contains a valve so the wall-wart supply is 9-0-9 V ac and 3 wire for an
internal step up transformer ( presumably , not looked inside yet), no great
problem there to do that.
But the connector on the unit is a 3 pin locking din, like CB mike
connector, but the pin spacing is non standard, 5.5mm between pins rather
than 5 mm.
Normally, in such
situations, I would change both parts of the connector to something standard
or just wire in through a gland.
Had to get inside to check the wiring as cold testing not consistent with a
transformer and no confirmation anywhere other than anecdotal/verbally that
the supply is 9-0-9 ac, centre ground.
That feeds a bridge R and then 7806 and 7906, 4 4580D smd opamps and a
12AX7.
Where is the HT supply ? caps are 10V,16V or 50V, input socket contains 2
crudely epoxied small unlabeleed black lumps with 6 pins
one has pin-pin resistance readings of 13K,360R and 0.1R or less
the other 18K,360,720, 0.1R or less
So perhaps transformers there, but smps combined with input amp in a can? ?.
A smd 8pin device marked AD 741 and OP 275G and a few TO92 transistors but
nothing SMPS looking inside.
Then the final test, the wiring to the valve. Whether plugs are in or out of
the 1/4 inch sockets the anodes of the genuine looking , but no label valve,
are connected to one end of the heater chain. No viewing hole to let the
owner see the presence of a glowing valve for the psychological effect of
the valve sound. Only + an - 6V to the valve to power the heater, no HT.
No larger voltages on the valve than the -6 volt and +6 volt to the heaters
and unit worked perfectly normally when tested .
Incidently note the various casing screw lengths, on disassembly as the long
ones would touch the pcb if replaced wrongly
Don't forget to add the 2 large spacer rings to the footswitch 
before fitting the board in the box.

NJD Spectre theatre stage light, 2003 date
Gives fully variable, total spectrum, floodlight output under remote control.
Or it would but nothing now. Full of dust and fluff in the control area and
a long term heat damaged , so presumably dramatically raised ohmage
resistor. First thing to beware is disconnect the lead to 
the NTC thermistor for heat sensing it is very weak 
at the epoxy glue point. IMO this should be 
in a PTC circuit as the controller will work with it 
disconnected. Also there should perhaps be an overall 
thermal cutout connected to the lanmp mounting 
plate. This NTC according to the schematic was 20K cold 
but I measured at 25K. Fan would cut in at about 4K 
but much higher than the design 50 degree C so added 
12K in series. As R6 is very close to the lamp 
mounting plate I suspect the whole unit had been 
overheating before the fan was cutting in.
Schematic available on request via email to njd.co.uk, not the same as 
this model.
The bands are only discoloured , 5 percent and 2W
size. Coluur bands look exactly like 100 ohm but 
measuring gives 47K , the same as the R6 value in the 
schematic. Replaced with 2 100K , 2W in parallel 
surrounded with ceramic beads to allow positioning out 
of the way of transformer and metal work.
The opto is 4 pin P620  Toshiba TLP620 , current going through
back to back parallel LEDs of 50mA rating with transistor receiver, presumably 
passing phase info to the PIC controller.
LED side of the opto seems ok at 1V diode-test drop either way.
The fan would come on and the lamps only control was 
on or off via the remote hand control and half 
brightness setting. Bypassing the i/p side 
of the mains side o/c then full lamp brightness 
only. I convinced myself 
that despite the LED going from red to "orange" signifying 
correct control pulses being received I thought there 
was a problem with the Tr/rec SN75176BP , i now know 
unit will work with a SN75176A. Easy to flip the 
DIP sw settings .
Seems to differ from the internet available operation 
manual for the DIP Sw settings. For single remote 
control then off/on/off .... , setting to that configuration 
brought full control back. on/on off... or on/off .... 
loses control function. The triac may that controls 
the fan may have been malfunctioning so replaced 
with a TO220 one

Norman NT100, 1970 amp
Severely worn track of the "middle" pot meant, except for 
a few small positions, there was excessive hum through the amp.
Removed all pots and reconditioned. Added a heatsink to 
the 3055 as seemed rather hot.
Uses 4 2N6254, 2N3055,ME8002 and BC18?C (184 ? )
Main board says Tuac TP 100W
Main ps 48,-48V
DC on smaller Trs and the 3055
3,0.8,0.2 / 34,3,2.3 / 37,2.3, 0.1
34V,43V on small electrolytics
0,48V across one W/W dropper .5,48 on the other 
and 48,43 across the smallest W/W
Preamp supply was either 43V

Ohm Solo SC60 , 1983
Speaker o/c and knocked out TIP tr, don't know 
which came first but final straw for the speaker, actually 
corrosion/work hardening inside solder point of the 
tag terminal.
Remove front speaker surround by 3sc under and 2 large ones  inside
Amp slides up and out after removing front 2 sc
Springline Accutronic 3106610, 670R/ 23R
65V ac
with 8R load, back line DC
-2.7,-16.3,-2.1
0,43,.4   / -43, 0,.42
-.5, -42,0
0.9,0,0.4 
0,43, .4
With ampremoved in free air and plate laying vertically with thermometer 
fixed on top edge
12 minutes to plateau at 23 deg C over ambient with 36mV in , 400Hz, 
giving 9.46V over 8R and all pots half way and 2 RED LED lit
2x RCA2N6254
TIP42C, TIP41C, 2N3440, 4 x TL072, 
4x .33R, 5x 4708R speaker, measured 6.7R when replacement 
pigtails made up and removed dome to solder into existing .
Tr 24R//1.3R

Pearl Octaver compressor, 1984
Would switch from bypass to function but not 
return , without unpowering it and starting again to reset.
Replaced the MN4007UB with CD4007AE (happened to be at hand)
That one of similar age failed in a different inverter 
leaving symptom of latching LED on or off 
but no compressor function, just as well I'd 
desoldered the original and placed a turned pin socket there 
in that case failure of pin 9,10,11,12 inverter

Peavey 701R 7 channel mixer, 1990
loss of signal and bangs on one channel and 
occassional whistles and noises on the other.
Remove all fixings on rear except the earth bond point 
to remove rear panel. The XLR surrounds 
come away with the panel. Temporarily 
replace the mains lead to facilitate.
Remove springline 59R and 193R
mains transformer is 237R but as 25H 
cannot measure with autoranging Fluke DVM
All 3 front panel switches were dodgey, as 
welded cases had to be replaced. Difficult 
as non standard DPDT though 2 could be just SPDT 
shallow format. Luckily had some ex-kit 
small ganged slide switch blocks with separate 
locking actions. Footprint different 
but could be bent to suit the pcb holes. 
Before removing mark cross lines on the pcb 
by lining up a pair of steel rules on either side 
of the knobs as they must locate with the front panel holes.
And used same button shaft size.
Rotated the interboard connector arrays 
and resoldered all the socket and pin sections just in case.
Wrong shape of solder pins for the holes so some of 
them looked to have had cracked rings around the holes 
and insufficient solder, so next time do this 
first instead of replacing switches first.
4.6 mm splined shaft, 8.9mm AF bushnuts pots. 
main supply interconnect
0,0,-24,24,-15.8,15.3,0,0
nothing much on the others
One pot shaft sheared and repaired as per tips 
as non standard pots and replacement knob 
as per tips. With the back panel removed make 
a ground connection from an input socket to the front panel.

Peavey 5150 , 2003 USA made
This is an export model for 240V/220V areas, no 110V option.
Demounted the switch and remounted with a cover over the 220V 
option as it was in 220V setting as received in 240V area
The mains lead has a German integral plug( 2 round pins and a removed earth
pin but an exposed earthing point) on the lead with a German? socket to UK
plug adaptor.
This adaptor is presumably used on other equipment for this purpose.
Despite BS kite mark etc it is a very vague connection between the earth
point of the German plug and the UK earth pin. In this one there is no earth
bonding as it is so easy to dislodge the plug relative to the adaptor and
losing earth bond , thin spring connection.
Adaptor is SCP3 made by PowerConnections , Harlow, England.
Needs totally removing German plug and adaptor and fixing a UK plug on the
lead.
Not a screw in earth pin but a push-in pin from a
socket for earth
Plug type number? TA-6P , and country ? designations
D, S, Fl/Fi?,öve,N
To get inside, leave handle on top , remove both pairs 
of side screws to remove the front and 4 screws at rear 
to remove the back and then remove the feet to slide the 
chassis out,
One 6L6 had a screen leakage problem , not 
obvious doing cold tests but after eventually 
getting a tester zero prior to mA/V test, 
neg grid volts of -4V or so varying to -7V 
should have been -18V. While still hot 
from this then showed leakage on the screen test.
2A HT fuse was "soft" blown ie most of filament 
remaining and no black staining. 

Peavey Bandit 65, 1983
Bad input socket.
Weakened metal on the U of these open sockets.
Opened out the U so the V tip of the contact is in line with 
the V tip of a plug.
Tied tight a cable tie around the curved section to reinforce, and 
the same on the other socket. No point in replacing 
these as modern ones will  be weaker anyway.
Reconditioned 2 of the crackly single pots, 
no need to de-solder.
Uses 2x SJ6392, only 4558, Motorola 339 and 326
3x 0.33R, 2x 500 , 0.22 and 220K (may have been 
4.2K which was how I read it , probably backwards, 
part of coating was missing).
Beware the speaker line isn't touching the casing 
at the exit hole on re-assembly

Peavey Bandit 112, 19Kg
Handle broke and then dropped amp and no go.
Broken handle because probably just one nut tightened against 
wood and so slackened and fell off. Needs at least 
nylock nuts.
Tended to the usual suspects, fuse-holders, 
big components and in this case the over-temp switch.
Returned to normal service.
The under slung mains transformer, probably a mod 
for UK as 240V only primary failed the earth bond test.
The mounting screws although not so loose to fall off 
with transformer following, they were loose enough 
to isolate from the rest of the chassis. Mains 
primary for UK about 11 ohms
PA board only looked at, uses 
70483100, 70473100, 5331 and another 
covered in spot paint , presumably 5332 
3x 4560
W/W Rs 4x 0.33, 2x150,5R6, 2x 2K
MO 2x 22, 2x2K7, 6K8

Peavey Black Widow speaker rebuild, 1979
Not made for the UK climate, stored in a (normal for UK) damp garage for 3
years, came out making nasty "amp clipping" noise.
I don't know how general this is for different manufacturers but for
unsticking the contact adhesive of the original cone and spider skirt.
I tried hot-air gun , oven cleaner and acetone but the one that worked on
the one I did this week was petrol. Some strips of tissue paper soaked in
petrol and covered with some circular strips of plastic and leaving for half
an hour to soften the glue
Now it is totally apart, small bits of aluminium oxide in the voice coil
slot were causing the distortion along with loose skirt biased to one still
retained side. 15 inch size with aluminium basket.
The voice coil is in perfect condition and no imperfections to the cone
despite 30 years old.
Prior to me getting to look the owner had removed the 3 magnet retaining
bolts and removed some perished foam filter from inside under the mesh cover
and squirted in WD40.
The white oxide formations had burst the glued skirt off , about 80 percent
of its rim, and the same for the cone rim (after removing the periphery
bolts) and nothing much holding on the remainder, easy to prize off.
masked off the central voice coil slot area before
abraiding back the lands to take contact adhesive to replace the skirt and
cone. Then air blast and run thick plastic around the slot to clear any
crud. The magnet does not seem to be corroded, shiney, no obvious rust
spots.
The 0.08mm thick aluminium dome must have been press-formed 
or by metal spinning with a cylinder
extension to the dome and the cylinder section is glued to the inside of the
VC former. So had to cut around the dome to remove and hope the
final gluing-back holds up against the air pumping process.
I just used 4 ball point pens in the rim 
mount holes for rough alignment and some clothes pegs to give a bit more
clearance gap for laying down the glue. Removed them prior to dropping the
cone in case they gave some bias.
I'm just wondering how much the "monocoq" construction of the Ali dome plus
cylinder gives circular stiffness/precision, that my cutting it has
destroyed. 
Voice coil 47 turns counted but doubled up ? , 
not checked or width, circumference unfortunately.
3.2 ohms , tested with 5V ac of 
10 Hz into 4 ohms with speaker not in the cabinet.

Peavey Cyberbass 5 , 1993/ Neutrik RP8 connectors
Noise prolems on the midi signal 
http://www.neutrik.com/client/neutrik/media/view500/Media_1128418177.jpg
Neutrik logo is a curvy 7, T, and then upside down curvy 7
Or rather the choice of lead, presumably a generic problem so a pre-emptive
fix for these leads required, whether new or old. Apart from fixing the
break in one wire on this lead. No abuse required, they will naturally self
destruct.
8 way midi and audio lead but no overall shield and the otherwise nice
rubbery sleeving compresses/deforms to next to nothing thickness under the
plastic crocodile teeth of the internal cable grip. So the teeth end up
pressing into a single
active (soon to be not) wire in normal use. Cut a strip of 
0.6mm thick expanded aluminium sheet to wrap 
around the sleeving and go under the crocodile teeth. 
Removed the pins ,ITF, and soldered back a fresh 
bit of cable. And because the solder blobs bulged added 
some hotmelt string between pins. The pin numbering , not stated in 
the Neutrik pdf goes with the snaking of the green colouration 
on the pin matrix. Beware these cores can go in the barrel 
in 2 diametrical positions, ie not polarised. Peavey 
has used the opposite, so the green blob goes 180 
degree round from the arrow on the barrel.
Decided to reinforce the sleeving on the other plug and one supposedly
crimped wire fell out of the pin and a grounding wire was broken in the same
manner as the other end, just retaining touching contact with inside of the
shielding foil of that triplet subset of wires.
Without the casing around the splitter the ground of 
the audio out is connected to the ground of the remote 
switch via the 8 way lead. 0.15V dc drop due to 
the wire in this case,
Excessive mains noise in "audio" mode, increased 
the 100uF,25V cap in the splitter to 470uF,40V. 
on the 317T, 8.5,9.5,24V
The noise now due to cross interference from the 
midi line along the length of 8 way lead.
The only way to reduce this is to turn off the 
splitter box and so guitar ps and plug a dummy 
1/4 inch jack in the normal guitar output to engage 
the battery .
normal output range about 70mV to 100mV pk-pk 
on different strings. Without battery in, 
impedance varied between 7.5K and 9.5K on guitar 
control settings. With no power to the synth unit 
impedance across the output jack was 250R

Peavey PV 2000, 2 x 1KW, 30Kg, 2001
Central TO3 of mainboard N and P sides is not 
configured as the remaining 7 TO3
Mechanical problems that need sorting before the electrics or will  recur.
Each channel has 2 "daughter " board output arrays with power rails via the
aluminium hex bar standoffs. One end has the screws nicely soldered on to
the main board conductor traces, but these standoff boards just screwed
against polyester pcb board, no star washers, contact (in theory) is on the
other side of the board, but not with loose screws. This amp is used in
alternately both damp and dusty environment so inside looks more like 20
yearold, aluminium corrosion etc.
Any mod better than cleaning faces and adding star washers ?
Also the clinch nuts that hold the pa boards away from the top and bottom
covers are just clinched into pcb polyester so easily turn and work loose,
any mod for that ?
There was one zinc plated nut with captive
star washer , loose inside, causing trouble. Now I've found another one,
lodged safely, in the base. Came from the IEC housing. The real culprit was one of 
the mains cable clamp bracket-looking pieces had dropped away and 
retained by the owner after he had looked inside. They are loose fitting ,32 TPI , on the other
0.128 inch screws used inside , so presumably 6UNC. As this is in the UK,
unlikely 2 would have fallen in the fan access , in a metric-screw UK.
Exactly these style nuts are used elsewhere in the amp , but the next size
smaller. Most screws in there are tapped clinch nuts or chassis steel.
This amp is 30Kg in weight  and because the clinch nuts are so small and
flexible top panel, so close to the pcb, someone has post-factory lined the
panel with sticky thick plastic sheet. You cannot extend the "nuts" without
modifying the single internal bracing metal (full-on engineering).
The found nut had no sputter or smoke marks unlike the pcb.
Re-clinching with a ground down cross point driver bit and anvil etc, worked
well, retapping with 4UNC , because of the corrossion rather than any
deformation by my action.
1 of the 2 nuts holding the IEC socket was off. I wondered why the owner did
not hand me the "lump of metal" that he discovered wedged in an active area,
he probably dropped it trying to retrieve it, from a visible but awkward
place. The screw was in place , with a tight fit , not threaded, through the
IEC. Owner out of contact for a few days, so stymied , in case I'm inferring
too much, ie 1 nut only.
More accidents waiting to happen, presumably because this amp is used
outdoors at full 2KW whack. Not only the screws holding the daughterboards
to the pillars but the pillars to the soldered-in-heads mainboard screws
undid in the range of 0.1 to 0.2 N-m , presumably due to creep of the pcb
polyester. So presumably a generic problem for all these sort of Peavey
amps. So 3 stainless steel star washers each on these active pillars, longer
screws and laquer over the exposed screw heads.
The hex pillars have been cut with star patterns on the ends which just
grind into the polyester on tightening. So I've changed my mind to abraid
the pillar ends , 3 st/st crinkle washers , longer screws and laquered heads
Looks as though the diac/triac is for crowbar protection of the speakers
from DC fault developement in the amp. On the assumption the mains trip will
trip.
Thermal swittch Asahi US602 S
I find one www ref to this as 140 degree F = only 60 deg C, mounted with
direct thermal contact on TO3 package, 60 watt in use,  MJ15025. Surely
higher than that.
accurate kettle test can only take to 95 deg C and no switch over.
Less accurate hot-air gun switches at 95 and reset at 75.
As there is also SELCO OA212 printed on the active contact face it is
probably, n/c,100 deg C
shorted SAC187 ( across speaker o/p) replaced with BTA16-600 
Test the 8V bidirectional switch diac marked C8D C1 ? 
= SBS/4 on a current limited 50mA >8V bench ps 
when triac is removed
70474200 replaced with MJ15025 and 70484200 with MJ15024
lower amp is "B" red power leads
Release rear, base and central galvanised divider bolts to slide remove 
the bottom amp leaving sides , front and 2 grey plastic bracing rods, 
undo earth wire bond screw
leave IEC and 7 amp cutout in place
mains transformer primary 2.9R
uses 16x .33R, 2x4k ,2x 5.6R, 70413080, 2x 4560d,
MJ350, MJ340, 6.8K, 47R
fan & o/p board uses 2.8K
mark orientation of LV board connectors as 
central one is full 5 way
90 percent of mains , 210V ac 
monitoring bottom amp ( top one removed) +/- 80V dc 
gain at +6dB , 0.2V 400Hz i/p 
gave 5V ac over 4 ohm, and about 1amp mains current

Peavey Rage 258, 2006
Blown mains fuse.
Replaced but intrusive hum/buzz on output 
and suspicious black ejecta on the output pin , 
replaced the LM1875T with TDA2050 
and high power 5V zener in each ps line.
Specced at 25W but running at +/-30V rails so 30 W , 
which for 8R load is in the device specs but 
seems odd as amp blew at very low loudness (so 
high rail volts ?).
2050 specced only for +/-25V
Tx 44R// 1.3,1.3R
1W 2x 470, .33R, 10

Peavey solo series, Bandit 75
Intermittent audio cutting out
Nothing specifically found but attended to 
the usual suspects.
Resoldered jack sockets
Reconditioned very worn/scratchy vol pot
One 8 way DIL socket may have been dodgey, 
replaced with turned pin socket.
Cleaned the effects socket bypass switches 
in case of corrosion there.
If it had returned then would have replaced 
other 3 DIL sockets and 12V DPDT DIL relay
O/P SJ6392 and SJ6505, 45, -45V on Cs
0.5,45,1.2V and -0.5,-45,-1.2V on TO220 devices
14.5,-14.5 to 15.5,-15.5V on ICs

Peavey TKO 115, 1992, 30 Kg
Nasty hum and tripped out a RCCD. Speaker 
probably had DC on it. Probably due to being 
dropped, one ps cap broken away and the other 
loose at pcb joint. 2 pots had broken paxolin.
Remove 2 top braces and rear angled screws to remopve amp.
Careful of these pots on removing the pcb as 
not really enough leeway to extract comfortably.
Had been repaired before with 2SA909 replacing the 
original 70473100 (MJ5016). Original 70483100 
(MJ5015) in place and both OK.
Also used  SJE5332 NPN  , SJE5331 PNP.
Resistors 3x150, 2x2K,2 x0.33.
ps +-50V, +-27V
Front grill frame needs banging in at each 
corner with hammer over a  wooden block 
(heavy duty velcro-like fixings) prize apart 
to remove

Peavey TNT 160 , 1990
Highly unreliable, assorted noises, hum etc, or no output 
after using external; input, to bypass internal prea.
5 of the 6 front panel jack sockets have duff solder. Not even with
lead-free solder have I come across such  .
What other problems with these sockets ?
http://www.diversed.fsnet.co.uk/peavey_0.25.jpg
sockets marked S/C, barrel/cylinder ground contact and sprung tip contact
with switch contact. A different 5 of the 6 have a crack in the plastic
showing at the tip of the yellow "V" - stress from manufacture ? metal bush
and nut so the plastic should not be compressed/stressed. The ground
terminal wire seem to be just pressure contact to the barrel to the left of
the V, with green copper carbonate? corrosion products, either side of that
ground wire.
In this case its that old problem of thin blade terminals soldered into
circular holes, so an enormous bridging gap for the solder in most places.
My usual retro-remedy is discs of fine brass or copper mesh, punched with a
paper-punch , and opened out central hole, soldered in place over each pin,
so mesh reinforced solder.
pcb test loop pin soldered soldered between each pair of sockets , plus 
2 more holes, silicone cordage tied around with a small ceramic bead over 
the contact blade to reinforce 1/4 inch plug/socket closure force.
Thread cord through loop before soldering to track on rear of pcb.
Earth point totally loose as were some of the pcb retaining screws 
from combo vibration.
Either or both ? loose mains earth or not tightened 1/4 inch socket nuts 
was giving electronic "phaser" noise, whether switched in or out, 
on reassembly until both corrected. As usual with Peavey, I don't like xternal 
240/120V switches in UK use and placed a solder tag under one 
mounting screw to physically hold off any drunk/thicko fiddling 
trying to "repair" the amp at some future stage.
Uses 2x 3034140, 2x 7048140, 4x .33R, 2x 2K, 2x 5.6, 2x 2.7K, 7815,
7915, 2 motorola TO220 , 70487478, 2x4558
prea NE572, MN3007, MN3101, LM555, 144558
transformer 5.6R// 5.2R, .4R
interconnects -14,0//-16,0,15,0//0,0
TO220 1.2,45,.55//-1.2,-45,-.55

Peavey TNT1155 B W Combo Mark III Series,1979, 35Kg, 130W
Series 260c
trannies maybe FETs TO92 size marked
Korea  TIE626 or TI6626 or maybe T1E626 or T16626
also a number 761, no equivaklent found.
pa 2x tl074, BD139, M926(0(?53?/5332, CA3904
70 4 / 874 78, RCA 532
The output trannies 67376 , RCA 
Bad crackles/bangs due to corrosion 
of Molex type connector pins removed 
pins using method for QM pins 
in tips files.
+/- 40V, +/-15V
10W, .1 and .33x4
Load tested for 6V of 400 Hz into 4 ohms 
heatsink temp stabilised to plus 
38 degrees C over room temp and .3V ac at 
preamp to amp connection

Peavey Valverb, 1994 valve / transistor hybrid
Valve Reverb, 1U case prob. 1994 , no output.
One obvious problem. Seems to be C-R-C-R-C HT ps with
the first R overheated to partially white body and O/C.
Scraped back and remnants measure 4K and 12 K. Comparing
with other MO 1 W Rs, band positions on bodies, the band heated to black
was
probably gold and the first 2 Brown then blue , third is gone totally,  .
so maybe 16K , replaced with 2 x 0.5W 33K, not higher wattage .
Supplying HT to 3 valves 12AT7 and 12AX7 so common enough.
The second  dropper in
the ps drop down chain is 22K and looks fine.
Apparently no separate secondary for heater voltage - seems to use the
same LV winding used for the transitor power rails.
Wax coloured hot-melt glue, not wax under caps which looked fine 
as well as all else.
What I thought was just an intermediary smoothing stage is actually also a
feed to a 12AT7 via a presumably impedance matching output transformer
 to A2 anode and the other via 47R to the A1.
This transformer unpowered resistance seems ok about 2K on high imp
side and 300 on low imp which directly connects to one of the coil
type transducers on the spring-line. So maybe excess current in this valve
hopefully rather than a failing impedance matching transformer.
I've only ever come across piezo transducers on spring-lines before
this is 56R on the send? transformer connected side and 196R on receive end
coils.
I replaced with same wattage R ,disconnected valves and cut trace to
matching transformer.
Powered up via variac to full, giving unloaded HT rails of 440V or so
sustained with no problems.
On load hopefully the 440V should drop to less than design
max of 300V.
Dug out my old Avo 160 valve tester , noticed
last
calibrated in 1984 for the REME in the Hebrides. Also powered up via
variac initially. All those thumbwheel switch contacts and other contacts
that
could easily corrode but no problems.
I'd forgotten about the sequence , balance mains V, heater check, cold
insulation then hot
insulation , Test and Gasified check. Also forgotten that nifty 'telephone
dialler' for set mA/V.
All 3 valves nicely in the green GOOD sector. For the 12AT7 design
value is 5.5 mA/V and on test is 5.4 and 5.9 for the other triode.
Ignoring the drop associated with the other 2 valves and not
at the moment knowing the actual anode current, if at the test
value of 10mA then drop over 16K would give a dissipation of
1.6W. I cannot find in the data book or tester manual whether
that is 10mA each triode or combined value but I assume it
is per triode and 20mA if both sections on at test levels so 3.2W.
Didn't think to check for primary to secondary short on the matching 
transformer. This was the problem , the bobbin is made of soft plastic 
and with time/temeperature the ends had flexed enough to allow 
some of the outer, LV, turns to drop into the HV turns area. 
Removing the transformer and deforming the bulk of the colis 
showed changing bridging resistance. Resistance of LV coil 310 ohm 
and 2100 ohm for HV. Weight excluding bobbin about 40gm. 
Average 'circumference' of LV coil 83mm and HV 58mm.
Wire 4 thou or 42swg so resistivity per 1000 yards 1910 ohm and 
weight 0.145 lbs. So by weight predicted number of turns 1150 
and by resistance 1790 turns. Warming up the coils with low set 
hot air gun and removing vinyl tape and waxed paper and mounting 
on coil winding machine gave counted-off number of turns 1800. 
Before rewinding adding some vinyl tape either side of the 
core and against the former, so that this coil doesn't slip 
into the HV coil through the gap.
As HV section left undisturbed then implied by resistance then 
about 17,500 turns for the HV section.
Representative voltages , no signal, controls at minimum
HTs 410V,246V,194V
At fuses 20V,20V ac
On 22uF electrolytics 0.6,0.6V and 4.6,17.6V dc
On the 3 valves DC
142,0,1,0,0,125,0,1,5.9
136,0,0.8,11.6,11.6,192,13,36,5.6
232,0,3,17.5,17.6,232,0,3,117
Also disabled the 240V/110V switch for use in UK - fiddlers 
moving switch setting in USA would do no harm but in UK 
a different matter. Some point in the future stops working 
so lets turn/move every exposed switch and knob.

Peavey XR600C, 1990
Signals at op sockets but only low level speaker o/p.
Failed bypass sw on graphic  "In".
Desoldered both graphic ones , cleaned up , added 
some silicon rubber under the contact and swapped over useage,
Replaced broken 4.77mm plastic pot shafts as per tips files
Ombilical green -15V, red +15V
400Hz 10mV signal gives .26V over 68R at o.p
PA 6 x .33R, 2x .1R
70484140 x 8, 7815, 7915
2x 2k,3x1k,5r6,2x .1R
4k7, 2W,22R
TL074,7048748
3x motorola TO126b 
mains primary 3.4R
Numerous bad or going bad solder points on the Swichcraft axial type 
1/4 inch sockets, presumably strained in use.

Peavey XR 886, 1997, mixer amp
Bad airflow, not to the extent of tripping any of the thermal switches but enough to
concern the owner into trying to improve airflow - admirable thinking for a
non-techie.
Blowing up into an adequate , for fan blown, heatsink with a bank of 12
motorola 70483080 TO3 . As far as I can see the 2 uncut-down heatsink vanes
that go across the fan do little functionally for cooling and probably
disrupt the air flow.
The air has to come in horizontally under the base , up the one inch of fan
axis and then have to abruptly divert horizontally again down the 2
(separated by these vanes) relatively small channels in the heatsink.
http://www.diversed.fsnet.co.uk/peavey.jpg
the 4 inch fan removed (position marked with
Fs )along with metal sheet that encloses the heatsink. The view of this amp
is upside down as the fan is at the base. So drawing air horizonatally
theough a "designed" 5/8 inch space under the amp. Air then goes through the
1 in of fan vertically and then has to sharply divert horizontally to flow
either way through the 3 ducts in each direction. The central duct contains
no active ducts and as far as I can see only interferes with air flow as
they are right up against the fan housing. Air then vents mainly at either
end when the metal closure in place with not enough space to add a fan or 2
at those points and nowhere near the mains transformer and main air outlet
vent . A lot of venting must go up and out the mixer pannel slider holes etc
as well. The 2 TO3 mounted thermal switches are marked S and restrict the
air flow through the uppermost duct in the pic, the leads and spades as much
as the switch body. 
Actual problem was intermittant loss of one channel 
dur to poor solder on a 1/4 inch spade buried in the pa.
mixer section not looked at
PA uses 2x MJE15033, 2x MJE15032 4x 3460 
2x Harris 7041 3080 
4x (2x250R , 1K)
12x 70483180 
4x (2K , 3x 0.33)2 x 5.6R
2 x motorola SAC 187 triacs
Changing switch selector from 220 to 240  dropped mains Ac from .8 amp to .6 amp 
with no signal throughput.
separate bags for screws from left , right , front , back, 
top, base, pa
55 - 55ac supplies
pin line under ch2/3 sliders, no signal
0,.43,73,.57,0,-.42,-73,-.55,-1.1,.27
lpoad test one channel giving 8V ac into 4R 
at 400Hz. Masking off whole of mixer section to 
block off air flow through there but not back panel 
so treated nor gaps between top and botton sections.
output air rose to 9 degree C over ambient in about 
15 minutes with extra 1/2 inch added to each foot 
and plus 10 degrees for existing feet depths. 
Fan came on full after about 10 minutes of such use.

Phonic 12 Impact, 12 channel mixer, 1981
Failure of pan operation on one channel.
More importantly the mains earthpoint did not have the casing 
paint removed either side of the earth tag point.
Each channel section is removeable after removing all bush nuts, 
XLR and slider screws. Uses 4558 and 2068 ICs.
Removed pan pot, reconditioned, squashed the swaged 
connections to the conductive tracks, resoldered nearest solder points 
reassembled and all seemed ok.
AC measured at the fuses 27,19,19,7 V.
PS uses C2336, 7815 and 7915
Molex DC readings 0,0,1.8,0.0
15,0,0,-15
15.7,0
C2336 , 2.4,68.7,1.9V dc
On main 12 channel 'bus' line 11 is -15V,line 12 is +15V.
One screw of the end cheeks is smaller than the rest.

Phonic 12 Impact, 12 channel mixer
Intermittant crackle, not able to induce via twizzle stick, 
freezing or heating anywhere.
Crackle was more high recurrance rate rustle than high voltage 
discharge. Changed mains fuse holder  fuse , internal fuses, 
tightened holders, changed +-12V regs, all associated 
electrolytics and remade all solder points on ps board.
May have been running hot with original V regs.

Phonic Power Pod 1062,mixer amp, from 2002
In for switch replacement but owner says he has , sometime back , got a
shock off the mains lead by touching the earth pin when just unplugged from
the mains.
The large conventional type mains transformer is mounted on a metal plate
that is held to the wood of the casing by 4 bolts. There is no earth strap ,
or ever has been , to this plate or transformer frame, so not earthed. The 4
bolts are exposed through casing on  base of the amp. 
240V , UK use.
There is just the input ground wire to the plate housing the mains fuse
holder. There is no specific bond wire to the main PA just relying on metal
brackets/spacers and self-tap screws "bonding" back to the inlet plate.
There is a yellow cased X1 .47uF , 330 V  neutral and live on the flex 
side of the mains switch .
So what class of electric shock do you call that, high impedance , DC , of
little medical consequence in itself, but surprise effect could have
indirect consequences.
The switch was tiny 2pole 3 way mode switch at an edge 
position just where someone put their thumb and pushed it 
in , disturbing switch action and crackling on one channel.
While in there to replace that switch , beefed up one 
of the most used 1/4" input sockets as per tips files.
pa uses 2SA3264 , 2SA1295
2x10, 4x 0.1R
n/c th sw, MJE340
On reassembly (master controls side first in ) if 
peak LEDs light then put the 1/4" bush nuts back 
in place for ground continuity, so if loose in use 
could cause this symptom with no input signal
load test with 400Hz, to give 8V ac over 4R 
for one channel (B) only 
9 degrees C over ambient after 15 minutes.
Fan on full after 10 minutes. 8V increased 
probably but difficult to tell with change 
of fan consumption affecting readings.
2 3/4" x 7 1/4 al plate , midway, over the top of heatsink 
and under top of case ,  
1/2 protruding to take thermometer.
Designed for air gap under the amp for this test

Prosound Minimix8 , Maplin, 2003
compact 8 channel mixer
Loud crackling on left channel
With twizzle stick located to a 36K 1206 format SM resistor, 
failed bond to one of the lands, replaced with 39K as to hand.
overlay Number not noted.
ps normal 2 amber LEDs on
15R,2W, C2383 ? TO92 device
.9(45V on phantom), 0,0,-,-,5,0,-17,0,17 on ribbon
7805,7915,7815,D2061 ?
The main pcb cannot have passed visual inspection test
as something in the wave solder m/c must have wiped 
down a strip of the board, smearing bits of solder with 
it. Cleared away the most potential problem lumps.

Quadratec VS450 slave amp,1996
4x 10N16, 4x 10P16, 4700uF  80V caps
1/4 spade connector of CT secondary only held in place 
by short leads and so half-loops of wire from Tx
Clipping monitor 1N4001 40V zener, 330R and LED

Rat, foot 3 pedal 
Could have been made anytime from the late 1970s going 
by the home-made feel of construction and basic 
plotter artwork.
Broken foot , then broken plastic battery enclosure 
screw , sort of held in place with gaffer tape 
but every time the switch was depressed , then trapped 
wires between 3PDT sw and batter case shorted against 
sw pins. Used 100K log pots and OP07DP

Roland Cube 30 Bass , maybe 2003
The box had been squashed and distorted in the hold of a plane.
A year later, reported as fuzzy sound on the bass guitar E string 
even at relatively low levels
but otherwise fine sound rendition or backing off the bass control .
Feeding a signal generator in then indeed a distinctly fluttery distortion
in the range 50 to 70 Hz on top of the wanted output, ok above or below that
range.
No external speaker output on this cube and before getting inside to scope
it or run an external speaker I took the front grille of in case of
parasitic rattling but no change. But putting a sock in the front/back vent
tube in the speaker surround cured it.
No problems with the reservoir cap solderings
Decoupling the negative black lead (not ground) via a 10u polyester cap to
the scope ground the electronic trace was fine at all frequencies and
powers. Semi-permanently blocked off the reflex/bass port or whatever that
hole is called and the intrusive 50 to 70 Hz induced flutter has gone. Just
the normal low level flutter , for low frequency, high power output due to
vortexing/cavitation or whatever the normal distortion due to bulk shifting
of air mass by a cone is called.
Blocked off the vent with a jam jar lid filled 
with hot melt glue and also introduced 4 plastic 
sleeves over the front grille retainer screws to 
push the front grille further away from 
the speaker.
Some tech details 2x TDA2050
270R, 2x 220,47, 2x .68 1/2W,
12.7,0,12.7V ac supply
10 inch , 8 ohm speaker
IC5 to red speaker lead
IC6 to black speaker lead, complementary fashion, 
not ground.
+,-,0 monitor points on the 1W Rs
270R is across the -ve rail cap
IC12 reg ? has 11V , 3.3V 
When out of the casing the 2 earth bolted leads need tying 
together for amp to function.
To monitor the speaker on DC isolated scope I bridged 
the introduces chock blocj connector with a C rather than an R 
to connect croc clips to. Although only 15nF this produced 
high f oscillation of 1.5MHz of a few volts so may be susceptible 
to stray cap. After all that the owner reported the 
same problem with another amp - the E string 
problem was with the Ashworth of Truro acoustic bass 
bridge transducer.
Sound colouration setting on Roland Cube 30
How the output looks, on an oscilloscope, for a
regular sine shape waveform from a signal generator as an input 
and using the "octave bass" option
 Octave Bass shape 
for various frequencies.
Because of image capture/strobe problem I've coloured in part of the missing
60 Hz shape in the top image.
The missing bits on the 160 Hz image are there but feint
Above 300 Hz the distortion disappears.
No distortion, as such other than level change, for these bass frequencies when any of the other sound shape
options are selected.
Looks as though the definition of "Octave bass" is it adds a subharmonic one
octave below the note in question.
Graphing out on a pc the sum of 2 sines of differing relative
amplitude and phase and fixed octave apart produces those shapes.

Roland Cube 30 Bass 
A sort of auto-wah effect at the flanger rate but with the effects controls
turned to off position. 
For working on these boards external to the casing , remove 
the heatsink and add a bit of flat metal to the TDAs temporary.
Looks like problems with the system of pots (nothing ohmically wrong) turning
to 0 ohm to switch off digital effects?, the LED goes out but it is as
though the micro doesn't know that.
Good sine signals through both sides of dual opamps IC1 and IC2, distorted
signal at both sides of same IC , IC3.
+/-8V supplies (2 TO92  near the main caps) to the opamps good and clean as is 3.3V rail for the
following.
Tracing signal back it seems to go to IC4 an AKM4552VT no data found but
AKM4550VT is an Asahi ADC/DAC of same 0.65mm format 16 pin but slightly
different  pinning.
Good sine in but distorted signal out so presumably the digital processing
is buggered somehow.
Tracing the lines back to the 48 pin IC8 Roland chip then pin 22 goes to the
LED and the wiper of the effects pot goes to pin 4 via 100R. 
Delay pot wiper goes to pin 5 of IC8, 3.3V on all pot end of tracks.
I don't
understand why with a few ohms left on the pot at "zero" the LED goes out
but the effect does not stop. presumably a drift in the 
IC8 internal sensing. Rather than trying to change the sub miniature
pot I added in a switch (thru front panel) to ground, via 50 ohm, 
on the pin4 side of the 100R, 
and 56 ohm over the existing 100 ohm, owner never uses the effects anyway.
Strung some stout silicone cord beween the 6 way 
switch ribbon connector and a cable clip clip around the board edge. 
Then some standoffs under to press both large 
SM devices in case it was poor soldering - nothing 
observed and could not make the problem return. 
If it bounces back then that 
will be the first task.

Roland Boss DR 55 drum machine, 1979
Just some 'top hat' noise but no drumming
The Vcc pin of the SRAM uPD5101 was corroded, no 
other pins anywhere on the board corroded.
Presumably something acidic left over from 
manufacture had corroded the part of this pin 
passing through the pcb.
'Vcc' should have been battery minus diode drop 
but was about 1.5 V less on this IC pin as coming from inside IC.

Roland micro cube, 2006,
9x8 x 6.5 inches excludes the handle 
Bad input connection, unless forced in one direction, 
not 2 years old.
How to get into the box? the bigger ones are easy in comparison.
Such a litle thing putting up such a fight. I've removed the speaker to have
a look inside and all I can assume is that it is just very strong metal/wood
glue locking the top panel part into the woodwork. The rear section is loose
of this L section panel but locked in place by the top section.
Its that double sided glued foam stuff, large areas of it around the 3 sides
of the top section. 
Eventually gained enough confidence to push a blade into the 3 to prize
apart, remove all 3 plastic pieces before any forcing.
post mortem on the Jalco 1/4 inch socket
No obvious problem but for minimal metal and plastic content and makes a
nasty scratchy/clicky noise on turning a jack plug in there, probably
because the tip contact is along the axis of the plug rather than across.
I suspect it was failure to positively disengage the grounding contact as
only something like paper thickness separation with the plug in place. I
could not induce the problem as found and had to take word of owner that he
had to bend the plug one way to make a contact.
Replaced with a chassis socket wired into the pcb
A 16 pin SMD IC with no heatsinking and drives a 4 ohm speaker of about 8
watts probably.
Markings,
TI logo
200001
67K
CC8C
Nothing found on TI etc but probably D class IC

Roland SH 09 , Synthesiser , 1981
New owner thought Ext I/P not working but 
only modulates interior oscillators when a key is pressed.
Remove rear + top metal section to get access.
Rennovated volume pot.
ps rails +15,0,-15V
Explored BA662 representative V dc
-14.3,0,0,0,-14.9,-1,-0.1,-0.02,+14.9
Maybe a pinned variant of BA6110 but the 6110 P/O 
in D.A.T.A books is patently wrong.
For BA662 looks like 
Pin 1 , control V ?
2  I/P with FB from buffer  O/P
3 i/p
4 Ground / Bias ?
5 -rail
6 opamp o/p to external FET
7 Buffer I/P from FET
8 Buffer O/P
9 + rail

Roland TR626 Drum machine
Intermittant power problems.
Beef up the soldering to the power inlet socket and glue with hot melt 
string to the pcb for mechanical strength.

Roland VR760 piano, 2003
Pushed in and broken solder joints on  dual 10K pot volume control and reverb vol control.
Need to remove bottom panel. Outputs board, dissolve the paint on the 
rear panel nuts (with paint remover gel) to remove main board 
with the flash reader. Mark all ZIF cables etc before removing. 
Remove the IEC board to remove the EQ panel.
ps voltages at main pcb are 15,0,-15,5.1,5.1,0,0

Ross model 10 practise amp
uses TDA2030, 0.1R

Samson Expedition EX30, 2001
Racing tape transport reported but not 
happening when I tried it.
Obviously been knocked as the mono/stereo 
switch was very bad, needed replacement as 
had been puushed in. The speed pot looked skew 
as well as loss of detent so likely problem as disconnecting 
the lines to that causes the motor to race.
Took apart and reassembled but no problem found 
Both 12V feeds need to go to 
the speed board to fully function
Measurements at 50K pot (mid detent )/presets 
disconnected from motor section
'0'preset 850, -12 1230R, +12 16.4K
10R next the 7809
With blue LED driven off sig gen in dark  room 
the motor flywheel speeds were 21.3Hz, 24.1, and 
27.2Hz at ends and detent.
on tape 7812A, 200R,1/2W 150R, TA8142
The 2 orange fibre washers are necessary to avoid an 
earth loop with the metal front tape unit panel. 
without them then a bassy rumble on the audio.
Problem was mechanical at the pimch wheel, lack 
of closure force due to bent/misaligned 
levers under fouling . Could not 
find the real fault in there and a loose 
torsion spring in the housing was probably associated.
Bent the metalwork a bit but that left the eject 
function a bit iffy , requiring play button 
to be pulled out before eject would function
12 in 8R,250W and 8R 50W horn.
Bottom section removal is possible to save the weight 
of 4 off 12V batteries.
Access to the pa is not via the side heatsink. 
You have to remove the speaker section , 
unplug the pa leads from inside , including 
the earth straps before you can remove
the pa via the side.
Most leads have DC function labelling on overlay
pa uses 3x2068, TA7313, 2x TDA7294, n/c thermal sw

Schaller acoustic guitar "pick-up"
Lead unsoldered/broken-away insde the pickup
Thick brass body so difficult to solder 
coax to it and not melt the insulation.
Drill small hole throught the brass and 
countersink for the head. Bolt inside 
a small solder tag.

Another acoustic guitar transducer
same sort of problem, wire can rotate 
and eventually breaks up at the pickup inlet.
No known make "Made in W Germany" 
and a delta shape logo. Cut away the lead to 
poke a rod in the hole to prize off the cover 
disc. Filed the slot larger to tightly 
take the wire and a nylon cable tie. 
Loop the tie tight around the wire on the 
outside and feed wire and tie tail inside. 
Pull tight and place another cable tie grip 
only on the inside to anchor.

Simms Watts AP50 , c1976 stage amp
No bass due to broken pot.
Supplies are 40,-40V and 17V
8V on the wire bridge of the pre-amp

Replacing a thermionic valve rectifier with silicon diodes,
ie "solid state rectifier" for 5u4, 5ar4 or 5y3 replacement
Measuring an epoxied-in commercial one , 
via a bench power supply, 
so low volts, for Fender
Combo amps and those 3 tube/valve types would suggest
pin 2 not connected
pin4 to pin8 , 2 seriesed 1N4007 (say) (cathode to 8 end), 0 ohms added
pin6 to pin8 , 2 seriesed 1N4007 (say) (cathode to 8 end), 0 ohms added
So no resistors added for "sag" it would seem
I assume there would not be a low ohm positive temp coefficient thermistor
in each diode line but could there be a voltage dependent resistor or 2 as I
only powered from a normal bench power supply.

Sound city 30R, 1987, GDR German Democratic Republic
Squeels and bangs and intermittent failure
Strange mustard yellow and more usual green copper carbonate 
corrossion in the area around both fuses. 
Replaced both by grinding out rivets, drilling a central 
hole and bolting in 20mm fuse holders.
Main caps 18 and 38V wrt ground.
3 loose cropped component wires loose on the main pcb trackside,
Uses 2x KD606 (70W, 60V, 10A NPN ), SD339 TO126, SF118B, SF828D, 
aand TO92 type ones marked
EW4 C37
EW3 C39
EW3 C38 etc
EW* is the date code and for C3 replace with SC33 and SC337== BC237, 
"C" is low power, low frequency, "S" is switching, "D" is
high power, low frequency and "F" is low power, high frequency.  
For reading these and specs/equivalents and other GDR components
http://www.elektron-bbs.de/elektronik/tabellen/ddr/transis.htm
http://www.elektron-bbs.de/elektronik/tabellen/datum.htm
http://www.tu-chemnitz.de/etit/zentral/ddr/index.php
http://www.dl7avf.info/charts/semi/siltmax.html
Reverb pcb has 30.8 and 20.8V on the extreme wires
reverb details tank taken but mislayed, maybe 300R and 40R
2 second hash noise at switch on is the same at switch off so probably 
normal power rail imbalnce issue, no relay, not failing cap.

Sound City 50 plus valve amp
One EL34 glowing excessively
Bad solder connection to the bias pot of this valve.

Sound Lab GTX 100 guitar tuner
Not a fault as such but a modification.
The Candleclub,Southampton
Is an amateur performance venue with mainly singer guitarists making their first 
appearance on stage where the noise,lights and maybe insufficient foldback make it very 
difficult for the unexperienced to tune their guitar up on stage.
A borrowed guitat tuner and one i donated to them both had the 
flaw that if left in line with the pickup lead whether the tuner 
was on or off meant reduced signal level to the amp. This is due 
to the monitoring circuitry loading the signal line.
There was just room to mount a standard 2 pole toggle switch 
in the box if the solder tags to the switch were cut down. Then 
one pole in line with the battery and the other pole cutting 
in the input. This required a cut in the trace between the feed 
through 1/4 inch jack sockets input and output where it 
branches off to the rest of the circuitry. Mounted (ruggedised) in a steel 
box with no top and one side missing to take the signal leads 
it could be left permanently in line with the pick up lead and be trodden 
on without coming to grief. 

Sound System Music Ltd , AC Euro, AC 360, mixer amp, 1996
No audio output.
Inferred history as bought at auction.
Someone had tried tracing source of crack noises,  
replaced one TL074 , not the one causing noise, with the wrong type of op-amp and 
also bent the pins forcing the replaced DC lead to the mixer the wrong way round.
Poor soldering on all ICs , not domed up around the IC pins, 
so one o/p pin solder joint bad.
First thing is polarise mark the indirect power connector, 
diode protected nevertheless .
Sequence is phono; from springline, to springline,audio o/p ; 
plus , gnd, -
No load DC rails were +-66V on 63V caps
Dropping 50 V over each 470R to give +-16V 
(15V zeners). Put some insulation on the interboard 
buses at output end as they were bent and could easily have touched.
Amp used 10P16 and 10N16, MPSA42 and 92 and 1R,3W
Silk screen pcb printing showed 5 amp fuses uprated to 6.3A and 
2SJ162 changed to 10P16 and 2SK1058 changed to 10N16.
On another occassion , bangs and pops on the output 
when touching the casing or lead yanking.
Solder joints failed on the thru-board pins on the PA that 
take the speaker lead wires.

Soundlab PMX 802D, 1984?
R channel went down after about an hour of use, 
recovering later.
Tended to the usual suspects. Protection 
relay and IC controlls both channels 
so not the problem unless relay problem.
8 pin SIL Marked C1237HA , on overlay PC1237 
and found datasheet on net under NEC uPC1237HA.
The leads from R and L channel (to one of the 
o/p device emitters) to 
the protection circuit annoyingly marked red and 
black , if disconnected will not 
disable th erelay click over
Most annoying there is not a standard 
overlay for the power device orientations 
on the overlay. Replaced one , with very 
bad green corrosion , the wrong way round 
and blew the amp. 
I determined the schematic for this amp.
Unusually all devices are marked on the overlay 
as their type number, not circuit numbers.
They all face the same way ecept 
the D600 next to the TIP42c, excluding the 4 
output devices.
Replaced 2sc2344 (tip41c on overlay) with 2SC4159 
and 2SA1011 (tip42C) with 2SA968
rails
Digital 5V and 8,0,0
main ps +/-48V
mixer ps -14,14,0,0,14
main board of mixer +/-10.5 V on op amps
-14,14,0,0,0,0,0, on ribbon
end board of mixer , on ribbon
0,0,0,-14,0,14,0,7x 0
240V primary 3.8R, <>0.15R per secondary
ps disconnected pa , "diode " test +/- to 
gnd 1.9 to 20V one way and >2.1V the other, alternate each way.
Load test of one channel with thermomneter 
mounted over the heatsink.
400 Hz giving 8V in 4 ohm load.
30 minutes to stabilize at 33 deg C over ambient, dropping 
0.5V ac in that time.

Soundlab SP 800 amp, 2002
Anyone familiar with this amp? worked for years with the present owner but
there is a quantity of circuit , each channel , that has been removed. A
"friend" decided to short a speaker line to give the current fault , but I'm
faced with a lot of post-production modification that does not look made by
the manufacturer.
Cropped tr legs and desoldered Rs,Cs, 4Tr,7R,2C all x2. Removed at
manufacture or previous owner?
Leaving this circuit in place with 2 Triac/scr. Unknown TO92 size SCR (on
overlay) marked (unclear on each channel examples)
08D
09
2 lines from the disconnected circuitry went to the left and rightmost pins
of that SCR. Nothing at any time to the centre pin. C is actually 2 back to
back 220uF, 50V for pseudo unpolarised C.
May need to change font for equal space font for the following


o-------------------------------|---o Speaker
         |                     .-.
         |                     | |
         |                     | | 10K
         |BTB24-600            '-'
         '                      |
        _|_/o-------------o  o  o
        V_A             SCR     |
         |                      |
         |                      |
         |                      |
         |                      |
         |                     ---
         |                     ---  110uF,100V
         |                      |
  o------'-------------------------------o Ground


Can anyone identify the SCR ?
I cannot identify as small SCR or diac in a 3 pin package, represented
as 3 dots, marked SCR  in the ASCII
looks as though someone else has been here with a different amp
http://forum.allaboutcircuits.com/showthread.php?t=23271
... The schematic calls this burnt component a "triac driver sbs bv thresh"
and on its twin (in the non shorted channel) its only labeled "08d 25". This
is in the protection circuit of the amplifier which unloads the outputs if
there is a problem.
...
This is a 3 leaded device btw
so the 09 in my case and 25 for him is probably datecode
googling about ,perhaps a DIAC08D, would that be an 8V diac ? sounds about
right value of bilateral switch for a 400 W amp into 4R
From that previous thread and mention of
MBS4993
I downloaded that datasheet and it looks as though a sort of Darlington
triac arrangement in the soundlab amp
The amp channel failed to s/c , knocking out fuse, so speaker protector did
not come into play.
The way to confirm the identity of this "08D" device is to
remove one and check for a switch action , at about 8V, on a current linited
bench ps.
Another oddity with this amp. Each channel has one floating, nominal zero
DC, connected to true ground by a 50 ohm NTC thermistor, why thermistor ?.
The missing circuitry may relate to fan proportional control of 1 or 2 fans
going by overlays.
Only one , on constantly, in this version. But why the 2 DC lines back from
the output on each channel. This is an all N-channel mosfet amp. Can they
have a DC offset if driven hard?
Inrush thermistor 3.3R
4x 0.1R, 2x 4.7 (at rear) 8x 1.8k 2w, 4x 4k7 2w, 2x 3.9k
Replaced one failed IRFP240 with an IRFP450
12x IRFP240, 4x C4793
One zobell R 4.7R, 2W colours had changed on over 
heating from yellow to brown, green to black, gold to silver
mains tr 4.7R, y-y 0,5R each ch
no load DC readings 
-74,-72.2,-74.5 / (-72.2,0,-76.2 ) x3
-74.2,3.8,-74.6 / (3.8, 76.4, 0.1 ) x3

Sovtek MIG 50, 1993
Rusian guitar amp using 2 off 5881 and 3 off 12AX7
Blowing the 1 amp "valve" fuse.
Each 5881 connected from anode plate to ground via 
390pF,2KV disc ceramic. One of these tiny caps that you 
commonly see in SM PSs had gone s/c between 
the leads. Cracking it open solder ? on the wired faces had 
melted /migrated across. Replaced with physically much 
larger 360pF ,HT caps on each 5881.
Wired the 110/240V switch paddle back to the transformer 
mounting so it could not be accidently flipped to 110V.
V dc with 5881s unplugged and 3 12AX7 present
 both 5881 sockets *.600,600,-61,*,0,0
nearest 12AX7 356,33,51,0,0,326,35,51,0
182,0,1.2,32,32,304,0,183,32
178,0,1.2,32,32,216,0,1.7,32
o/p matcher Transformer dc ohms 53 each winding 
and 1KHz ac L of 3.2H each winding and 19.4H end to end

Speakon loudspeaker connectors
(and pirated copies) 
, I noticed the R symbol on a Neutrik line plug
(4 way) that was mated with a no R, Cliff (2 way or maybe only 2 of 4 way)
chassis socket, they meshed and locked together and functioned fine as far as
i could feel/ see.
Apparently the 'blue' series are rated at 20 amps at max 120 volts.
Neutrik NL4`s are rated 30 amps for the 'old type' and 40 amps for the 
newer X series.

Spirit Powerstation 350 (Soundcraft) 350W Mixer / Amp.
Mixer OK but no power outputs.
The mute lamp (speakers disengaged) permanently lit.
Nothing wrong with the pa it was failure of the protection circuitry itself.
1/4 of the LM2901 (driver to relays) had o/p held to negative rail.

Spirit Powerstation 350
No power o/p,monitor o/p ok
Failure preceded by clipping LED illuminated falsely ie no clipping.
Probably one TDA7294 failing putting DC on o/p then second TDA 
blew and muting circuit cut in. On powering up excessive heat on 
main heatsink but all fuses OK. Trying to isolate which of the 4 
power ICs failed removed pairs of fuses and a 100uF,63V cap 
blew up. Without + and - 42V to the o/ps there is -15V on the IC 
and reverse polarises some of the caps. This associated 
(third) power IC was ok just a blown cap. Both failed ICs were 
resistive to -42V rail. Good ICs ,out of circuit, about .5 +supply 
pin to o/p pin on DVM diode check and about .5V -supply pin 
to op pin. As resistive rather than short took a lot of 
current but not enough to blow any of the fuses.

Squier sidekick guitar amp.
Broken away pcb from the front pannel
Weak 1/4 inch i/p socket had the back-nut come off the bush which meant 
user straining the pcb when plugging in the guitar lead leading to breaking of
 all pots.Replace with i/p socket mounted on the chassis and wired to 
the pcb and replaced all pots.

Squire Roadrunner Junior double disco deck and amp
OK driving one 8 ohm speaker but distortion driving 2 giving 4 ohm (designed limit)
The power output monoblock presumably has 4 o/p devices 2 in parallel 
for +excursion and 2 for -excursion.One tranny had presumably gone 
o/c so expensive monoblock replacement.

Sqire fog machine,no model number but 1993 and 
using MC1458N and LM324N on main board.
No smoke output.
No snubber network across the solenoid glycol pump so added one 
and changed the blown triac with a higher rated triac.

Studiomaster Powerhouse 8-2 500W mixer amp
For renovation of sliders but a few points in passing.
The fan duct over the power devices was half clogged with 
fluff. R53 and R68 10ohm,1W resistors were charred and 
replaced with 3x3.3W in series. There are a number of 
non-localised and non polarised interboard connectors on 
this m/c so mark before removing and make sure on reassembly 
not be 1 pin out ie 0to1 ,1to2 ,2to 3 etc.

Studiomaster Powerhouse Vision 8, 1996
Left channel clipping, then dropping out totally after a time, first problem
in preamp, imbalanced gain, second unknown pa or prea. At least possible to
swap the pa channels over, to resolve to pa or prea , if
nothing actually found.
Fan startup, comes on at power up for 2 seconds
(presumably normal) switches off and comes on whan heated.
I've never seen that before, a TO220 device trackside under each pa pcb,
thermally touching the heatsink. Only 2 pins used, the B-E junction, with 2
isolated traces to the umbilical ribbon the carries the low voltage rails
and signal i/p. I wonder what is special in the 2SD1763A used for that
purpose.
I've not got the schematic but I've found you can run it stripped down.
Disconnect the 2 PAs and all the ribbon cables except the one between the ps
one, via small rear panel and up to the mixer. To check for any mixer
problems, removing display and memory stuff, monitor output by phones.
You can then plug in one amp at a time , or
swap around , to localise single channel problem to one ch or the other in
pa or mixer section.
ps ribbon to mixer socket on main board under/between ch8 
HF pot and REV slider
There seems to be odd power rails , +/65V main power rails and a pair of
+/79V.
With pa's and mixer removed and Conn3 and conn4 ribbons removed, so just the
main combined ps and thermal board in place, DC voltages on con3
80,0.2(£),15,0,0
-80,16.6($),0,0,0 (*)
2x5 header volts viewed/monitored at pins , starting from main caps
end
* has 0.6V ac, and £ has 0.2Vac on it with 400Hz input and 0db bar
registered on the meter
$, 16.6V via 100R to base of thermal monitor TO220 ,to test point T12 ,
obviously drops down to Vbe , with pa in place
T10 for the other amp TP
The 0.6V ac also on that pin of conn4, clear and balanced , unlike
originally with all connected, very marked signal imbalance. There was a
problem with the "group" slider , but maybe not the cause of original
problem. I will next try with swapped pas in place, then display board if
all seems well.
At 75 percent or less of mains voltage both red LED "fault" lights light,
gives some sort of check of functioning.
I don't know what temperature is required to activate the yellow LEDs and
channel/channels ? shutdown, but presumably greater than 90 deg c.
You can monitor signal in of the PA at R11 , R9 end.
Monitoring output and T12 TP, increasing the heatsink temp with hot air gun
and fan off. No change in output level up to 90 deg C.
With fan connected , fan comes on (at T12) with  Vbe between 0.61 and 0.62
and temp between about 45 and 55 degree C (the "thermal" Tr is underneath),
dropping to 0.52 or so at 90 deg C. Both channels checked like this.
with zero on FB,REV,aux and centre for all else per ch.
 0.1V  input , 400Hz giving clipping point 
max slider, required gain settings between 45 and 55 db for each of the 
8 channels, both sides L & R
purple 116V ac supply
orange 38V ac
check main rail 1/4 spades are recessed before powering up 
disconnected .
To work on the PA and mixer , make extender for the 16w ribbon 
from conn2 of display board and conn under PGM/Edit led .
2 G cramps to fix a piece of gaffer taped dixion vertically 
in the front RH corner and small cramp for top 
of dexion to the mixer panel held vertically above and over back plate.
5 amp mains plug fuse is tool for this torroid.
Added 4 football studs underneath the case, as manky rubbery sheet there.
0.125V, 400Hz i/p at ch1 with full slider , 23dB mid gain, 
mid position of pots, 0dB on master slider , 0dB on bargraph30mV on pan pot 
and 0.56 V ac on R11 of PA resistor
With fan disconnected and 400Hz , 0.1V, 23dB gain, 0dB bargraph , 
3.3V ac over 4 ohm, one channel
thermometer bulb over centre of relevant heatsink cover/locator "pcb", took 40 
minutes to stabilise at 26 deg C over ambient.
The VFD display is very exposed/vulnerable with the mixer pannel 
mounted vertically for testing purposes.
Remove the short ribbon at the rear plate , not under the 
central screening plate. When reassembling I managed 
to trap and pierce a ribbon with a mounting screw, disabelled whole 
of mixwe pannel but no colateral damage other than repairing break on 
line 6 from red on the 14 way lead from front phones board 
to graphic board. Captive nuts not very captive 
so loose end covers/handles. 
Really a 2 person job, one holding a dolly and the 
other hammering a small cold chisel radially into the swaging. 
I tried a large ball-bearing in a cramp but could not 
find a suitable anulus to go round the ball to keep it in place 
while tightening up.

Sunn alpha four , 1978, mixer amp
Broken pot spindles, the fourth,offset, terminals are not 
bass compensation , just support.
Uses 3x 2n3055, 3x SJ994
2x 140, 4x .33, 2, RC4558, TIP 29
primary DC , 14.5 ohms

Sunn SPL 7000 high power amp
No output either channel and no known history
2 of MJ15023 B-C s/c replaced with MJ15025
Q118 2N5401?
burnt Rs R133=? R160 =100R
C55 .1,100V ?
R109,R110 = 22R ? had gone high
R121 422R
R111 430R
R134,R135 2.2R were o/c
Other Trs C2168,C1567-S,A958,
Q20 A968B
Q22 C2238B
The fan on this amp (UK version) used a 110V 
fan with a dropper so at low temp runs at 50-60V 
then switched out to 110V off the main transformer
In working order each pair of 15023/15022 showed 
.44R E-E and 4.4R B-B
Beware 1/4 inch jack needed in B input for single 
channel use.

The Talk Box HT 1
16 ohm speaker with capacitor so no 
DC ohms response on checking in/out/bypass function.
Requires mono jack plug on amp side input socket

Tascam 244 Portastudio ,1985
Broken tape control buttons and muffled,trebley low 
level o/p on one of the channels.
First to remove top cover leave all single knobs in 
place and lower halves of double knobs or the black 
felt skirts will fall off on inverting m/c.
Remove other slider and switch  knobs.
From underneath remove 4 screws and 2 plates holding meters in place.
4 corner screws, 2 screws either side of mains transformer, 
1 screw under 3/4 meter and 1 under ch2 meter, central long screw , 
tape-head access cover plate and one screw next to master slider.
To replace this cover place over the 2 phones sockets 
and align with the mains switch button and finally 
align the 4 meters - wiring-loom comes in at meter 2.
For normal operation needs jumpers on each send/receive 
at rear, without is low level distorted output.
The line in amps/equaliser boards can be swapped 
to localise problems - the 5V rails are chained across 
on the 2 wire leads.
Tape deck - aligned broken buttons and 
reinforced with thickish polythene for hinges, 
held with hot-melt glue.
Record function needs LED flashing then Rec plus Play
Problem with one channel was broken conductive track inside 
the slider pot.

TCO-1 compressor
uses BA6110, 6458

Teac/ Tascam Porta-one studio
Failure to record tracks 2 and 4
Broken track inside of master slider pot (similar to 
remaining pots so check remainder at same time)

Teac / Tascam 144 Porta-studio
Excessive squeal from the tape transport.
Cleaned the main slip-clutch felt but no change,still 
too much back-torsion so replaced the main internal 
spring with a lighter guage also replaced the small 
left-right throwing slip felt.Also put a 5V,3 amp zener 
in reverse parallel with a 3A rectifier in line with 
the tape transport motor to reduce the amount of 
slip and consequential vibration in play or record mode,
of course it reduced speed of FF but not REW.Do not 
run m/c with the tape head connectors disconnected as
the meters are overdriven with noise signal.Also be 
careful of aligning the tape transport first rubber pulley 
and also the solenoid arm when reassembling the two halves of the tape unit.

TOA MX601 Powered mixer amp approx 1987.
No main output but output on the foldback.
Probably due to being dropped there was loose connections between mixer/preamp 
and main amp. Gain acces by removing front panel first then springline (label before removing),mains transformer 
and rear panel. Long term problem of overheating of one trace to the pot on the 32 Hz section of the equaliser 
leading to burning off of the varnish and just started lifting of the track. Bypassed with wire..
General note 4 off 2SC3182 paralleled and 4x 2SA1265  paralleled. Cold "diode " testing no load 
gave readings referred to bases of ".46V and ".15V" for all (reversed polarity for one set of course).
Replaced master volume pot also. Although looking like 4 terminal pot the "mid-track contact" 
is a dummmy for mechanical support only.

Torque T100 B, 1992
Vibrating grille and worn volume pot
No grille support on 2 edges.
Undid the corresponding central carcass screws 
and replaced with longer ones screwed with cups 
through through the grill and a stack of rubber washers to pad out.
Uses Celestion K15-100
2x 3055, Tl071,72, CA3094
2x BD535, BD536
2 x 0.22, 2x10R , 2x3.3V Zener

Torque Trio 30W practice amp,
Probably dropped and jarred one of the lt ac fuse holders 
to o/c connection.
Uses 2x2N3055
Resistors 3x330, 2x0.47

Torque TK50 1969/1999?
Fades down in volume after 10 to 30 minutes
Uses 2x2N3055
Resistors 3x680, 2x0.47, 2x 072, 071, 15V zeners
28-0-28V ac
+/-41V,+/-15V
Replaced the phones and loop 1/4 inch sockets 
and reconditioned vol and treble pots, not necessary 
to desolder and attended to both select switches. 
 Maybe hardened grease on the tracks, no 
obvious wear.
glass thermometer to heatsinks (uppermost) 
8R dummy load test, 4Vac , 400Hz, 10 minutes 
to stabilise at 43 deg C over ambient and 0.05V drop.

Trace acoustic TA100R, combo , 1994
Loss of reverb effects. But of course when I try it all present and correct.
Attending to the usual suspects ,cleaned and put sets on indirect connector 
pins , removed DIP and PLCC chips and cleaned, also NE5532 , 
added 8 pin turned pin socket as original not very firm
Owner reports that the moveable notch filter has never worked.
I try it with sig gen and operates over 120 to 1200 Hz , noticeably reducing
the throughput.
The notch f spread should be a tad lower.
Don't know if the epoxied block is cutout/excess gain control or "Dynamic
Correction" (TM) apparently for correcting speaker induced distortion in the
pa. I assume the latter as TM and otherwise presumably unnecessary epoxy.
The 5 wires are opamp +&- DC rails , pa and ps ground lines (about 0.2R
between the two) and a line to the + i/p of the pa preliminary 071 op amp
Presumably unconnected problem - this 1.5x1.5x1 inch epoxied
block  fallen (safely because of plastic housing) against the
power transistors.
To gain access 1 sc at top, 3 sc under, 2 sc either side at front and 2 large at rear.
Use a screwdrive rin the top mount hole to lift the 
chassis over the corner braces.
Abot 0.1 or 0.2R between ps and pa grounds.
uses J50 , K132
o/p board 150R, 470 al clad, 7805, 2x 072
prea BD677, 5532, 5x 072
pa 2x2.2K 1/2W browned, +/-60V
Breaking effects return socket switch means reverb only signal 
not main signal.
power interconnect -15,0,0,60,0,0
R78 60V and 40V over
+/- 15V on 071
50V on cap next to ZD3
4x 8R 5 inch speakers
Renovated the pot with push pull switch , sw part 
as had hardened grease as in tips files
Blanked off mains voltage sw 
Grey ribbon connector on rear board 
requires removing glue and push down to release
Don't try removing the dual LED, put a 3 
pin junction on the board
Phantom 50V on ch 2 i/p (no warning LED)
o/p B of NE5532 to green ident end of ribbon 
to effects board
ch1 and ch2 rev sw to pin 6 of NE5532 
and pin 6 of IC3
preamp opamps seem to have "ground" at 
midway between chassis ground and 30V wrt chassis
If on reassembling just mains hash noise 
then probably trapped the main DC rails lead 
along the side edge of pcb and pulled off
Position 14 is 500mS single reverb setting 
, as the switch is indexed.
One of the profiled LED decided to fail from 
moving, the larger type with changed insulation 
around legs and cut down pip length , fitted in.

Trace Elliot GP12 AH250 SMX, 1994
plug tip of output lead touched guitar strings and amp 
died. Whether due to static or shorting unknown as 
"ground lift" may have been open or closed.
Poor contact on the 240/110 switch maybe due to the 
grease turning to something like varnish.
Once extracted from the chassis it is easy to open 
and clean off corrosion.
If due to static changed the 4011 and 4066
Poor heatsink integrity on +-15V regulators 
and the 2SJ50/2SK135 presumably due 
to pcb compressing under the screw pressure.
169V (on ECC83 load) derived from Cockroft Walton 
diode pump circuit ladder uses 072,074, and SSM 2034
2x 470R
+-68V and 20,0,20 V ac supplies

Trace Elliot Series 6 1215 200W 1989 Bass amp combo
Would run for 20 minutes or so then output would cut out but preamp signal 
indicators still showing first stage ok. Switching off at mains and on and would work 
but perhaps for only a few minutes . When cooled down totally then back to 
20 minutes or so.
The 20 mm 10 Amp fuse holder for the speaker line was not man enough.
Next to the heat sink it would heat up and internally distort and break contact. Physical 
vibration action of switching the adjascent mains switch would make contact again. 
Replaced with 1 1/4 inch chassis fuse holder and 10 amp fuse.
To remove the amp chassis remove 4 off blind grommets to reveal screws 
and slide out to the rear and tip up to give clearance for the speaker lead
Uses 2 off each 2SK135 and 2SJ50
39V on preamp board large electrolytic and 60V at + on power amp board.

Traynor 6400 Mixer Amp
No LED bargraph power display
replace the signal diodes at the point
of monitoring the o/p current

Traynor YBA1 Valve amp
Symptom reported as low distorted output
Both 470ohm,10W HT droppers o/c.

Vesta Voice MR10 (cassette based mixer and 4 track)
Minor faults then no tape play function 
Minor faiults:tiny piece of iron? stuck to magnet in one of the VU meters 
causing it to stick;dry joints on 2 of the 1/4 inch jack sockets ;slider pots 
needing lubrication as did the sliding mechanisms on the tape deck.
The plastic play key / actuator had sheared,plenty of available space 
but minimum of plastic used.The part is a channel section so filled 
the channel across break with hot-melt glue and a metal pin.On other side 
braced across break with small pieces of expanded metal aluminium and hot melt 
and then bound round the whole lot with strip of this ali and hot-melt.As a 
preventative bound all the remaining keys while dismounted in 
similar manner.

VOX AC30/6 TB, 29Kg
All valve, no solid state devices, probably made 2002 from barcode date? and
2001 date on Sovtek 5AR4.
Powered on for about 5 seconds with cracks and bangs then HT light went out
and dead.
Inside looks and smells fine but "gently" blown HT fuse. 
1 of the 22K 1/3W HT R/C dropper resistors slightly discoloured and all 4
EL84 1/2W, 100 ohm grid resistors slightly discolured. Someone has crudely
cut one of the 2 grounds to the pcb, presumably trying to reduce hum when it
was working.
All DVM DC resistance measurements of the transformers seem ok.
Probably the most diagnostic feature is the 500mA HT fuse, on the DC side of
the rectifier tube, is a small gap in the fuse filament with a glob on one
broken end, both remnants axially present in the barrel, no staining inside
barrel at all.
The third EL84 tested , started out normally then rapidly accelerated off
the scale. I've never had the protection relay on my Avo CT 160 dropping out
before.
Large Rs
2x 100 , 2W, 4x 100, 4x 1.5K, 
Left the slightly discoloured pa resistors 
as they are metal-oxide and would act as protection 
devices if over-driven.
On powering up again there was an excess of hum and no 
bass control. I'm not quite sure what was wrong with 
the bass pot . Probably something to do with how tight 
the pins were in the pcb holes, maybe bad solder rather than broken 
contact inside the pot but replacing it removed 
that problem and replaced the rather superfluous 
looking earth connection (formed a hum loop possibility ?) 
as may be a safety issue. To tighten 
the pannel switches a bit of 3/4 inch pipe 
hacksawed and filed to leave 2 diametrical nibs.
All the crimp connectors on the speakers were loose.

Vox AC30 6TB, 2002
Normal or abnormal ?
Came in for an intermittant problem, fixed, and the following the owner
lives with but is it normal or abnormal?
With feed into a "normal" input and the "brilliant volume" at zero then
there is no control of the bass on the tone control, you need to have a
little advance on the brilliant volume.
Maybe failing C10, the common cathode decoupling of the first valve 
failing and letting some signal through from the normal to brilliant section 
but not confirmed.
V7 ECC83 
DC voltages     cathode,grid,anode
"brilliant half"     0,1.4V, 182V
"tone half"         182,183,290V
V8 
62,42,234V / 236,43,62
all associated pots ,Rs and Cs check out agreeing with schematic as does the
valve and same Vs with a different valve
So normal, in summary, for this amp
There is treble control but not bass control with "normal" input and zero on
brill vol

Vox AC30 / 6 TB ,all valve combo from 2002
Rattling noise on bass
Ideally identifying which and dismissing the roady would make more sense for
this locally based band.
Failing that - concerning cut grommets encircling valves to act as retainers
in inverted amps. Lining the holes in the chassis where the valves pass
through .
a/ fairly rigid rubber of otherwise standard trunking grommets
b/ fairly tight to the glass envelopes to function as retainers.
c/ obviously  they do not take much of a jarr to cause breakage as no obvious
damage to the cab.
The 4 o/p valves have spring retainers.
One of the ECC83 (number 2 valve from the output end) quite neatly split in a ring where the grommet lies and
white getter in the cap.
I am thinking of running my plaited, high temperature silicone cord "rope",
over the tops of all 6 of these small valves , located over the top "pips"
and anchored to the chasis at the ends.
Run some thicker silicone sleeving "hurdle-wise" alternating over 
the tops of the valves with some small loops of twisted 
ptfe tape just in case they slid down.
Solder tag added to fixing bolt of the choke 
at one end and then the other strung a piece of cord 
between solder tag on the output pransformer bolt 
one side and a hole oin the chassis corner on the other 
to clip the main tensioner over with a solder tag as a hook.
An alternative would be silicone rubber cord/sleeve/plait 
anchored (in line) at each end and just wound round each 
valve with reasonable tension in the cord.
For checking the bass pot cold desolder R7
Treble pot top end to C6, wiper R5, bottom end C4
Bass top ground, wiper R7, C4
cut top C1, wiper C24, N/C
Excessive mains hash and hum due to dirty input contact 
- at least all 6 of those are easy to get to.

Vox AC30 / 6 TB
loud crack noises.
Someone had spilt beer into the HT switch and tone cut pot 
and some down onto the HT area of the board.
The main problem area was the beer that had settled into the 
switches and coated the contacts.
Uses 2x 100 2W, 4x 100 .5W, 3x 1.5K
choke 420 ohm
primary 9R, HT 73R
o/p 53/59Rprimary, .4R secondary

Vox AC30 , AC30CC1, 2005, (also see AC30CC2 similar)
To remove amp disconnect the front brackets and 4 
screws holding the amp underneath and remove the 
wood bottom to the amp when removed from the cab.
Without any input,
High sensitivity to touching the amp leading 
to crackles, flutters and pings exactly the same sound 
in speaker as flicking any of the inch long 
wire bridges on the preamp board which had poor solder 
on one of these bridge wires. Impossible to localise 
with tapping any board components as all responded but 
an artist's brush touching the relevant valves 
would show a response not shown by pcb conmponents,
On cathode/heater insulation test my tester scale 
only goes to 25Meg. Where leakage effects only start 
when the heater has been on for 10 or 20 minutes I 
switch to 10V for about 3 seconds maximum and return, 
assuming 6.3V valves. Two EL84 leaky, one 
after about 20 minutes from cold so 
requiring the 6.3V to 10V heater test 
procedure to find it as only marginal 
deflection on the meter scale) as well 
as one of the 12AX7. One of the Belton 3 springline 
springs was loose , removed and left with 2 
working as very frail ferrite or magnetic rod 
snapped at the pickup. 75 ohm on i/p 
pickup coil and 220 ohm o/p one.
Vox speaker 12.4 ohm DC resistance.
ps 50 / 5W,82,2x 10K,2x 220
preamp 2x 470,2x100, 3.9K
C2910, LND150 fet
For Russian valve cross-reference
http://my.so-net.net.tw/tube/power-tube.htm
eg (for "n" read Russian "l" that looks like 
the maths "Pi" symbol)
6n3C = 6L6GC
and 6n14n EB = EL84
useful for having pictures with the Russian script.
Output temperature monitoring
Al plate 3.25 x 7.25 inches folded to 2.75 x 7.25 
and 2 bits of plastic binder spine to thermally decouple 
and fixed with some wooden pegs to the Al screen 
next to the EL84s
Seting amp to 8 ohm and 8 ohm dummy load.
400 Hz signal vol adjusted giving 6V ac in the load,
over 1 hour temp of thermometer fixed to 
the plate increased and stabilised to 
20 deg C over ambient and volts dropped to 5.63V ac

Vox AC30 , AC30CC2X, 2005, 38kg (also see AC30CC1 similar)
Cured the main troubles in valve preamp and amp, suspect EL84 
cathode/heater leakage and 2 badly
soldered pcb wire links (lead free solder again, note only 2 or 3 years
old) . But there is a low level throbbing rumble noise
obviously associated with the tremolo oscillator , as it
cycles up and down with varying tremolo pitch and depth.
Associated with the HT as when tremolo depth increased to 
maximum the green "standby" LED flickers at the same rate.
This throb noise is due to loading of the HT which goes up and down with
tremolo speed and depth. With EL84s in and all 12AX7 pulled the throb is
still there, no signal throughput of course, even makes the standyby LED dim
in sympathy when at the deepest depth. Only stops if I disconnect the ribbon
that goes to the tremolo pots to kill the tremolo oscillator. 
To get to the valve preamp board, remove the wood 
covering to pa section   and desolder the thick wire interconnects 
on that board and pass through the gap to release the 
pre-amp board.
Leaving, likely ,just a JRC 2147D high voltage dual op-amp (+/- 28V not
300V) and a 2SC2910 associated with the tremolo area and something marked
SiLN D25D or SiLN D250 a 3 pin TO92 device, the S being the Nazi SS
lightning flash S.
Angled/Jagged Si logo is probably Supertex, so from their site its a LND250
500V, 3mA ,1K RDS on, n ch MOSFET but depletion mode , even as a SOT23 package, 
500V rating
The LND250 had failed, didn't pass the DVM diode, lead swap, test.
Erroneously replaced with a non-depletion type n channel Mosfet but at least
the rumbling had gone. Owner always ran it with minimum tremoplo speed and
depth which gave minimum throbbing.
Still no tremolo function. Now to find a 400V to 500V depletion mode mosfet
from somewhere.
This mosfet is connected via 220K to the HT line.
I thought tremolo just bent the frequencies in a cyclic fashion.
If something is as rare as hen's teeth then bodge up a
work-around with standard parts.
This high voltage , but depletion type Mosfet, is an active part of the
tremolo circuit , there is no separate oscillator. So re-biased the mosfet
up a few volts.
Using a TO220 size standard IRF740 enhancement type, fudged pinning, bled
off the 28V line with 91K and 100K multiturn preset 2.7V zener, for 
about 3.7V  
off the wiper and 27 K to the gate
, now have a fully working work around this tremolo problem. Full
range of 2 to 20 Hz or so and 0 to excessive depth. Its a bit too critical
on preset setting but the owner had not used the tremolo for ages.
For the archives , some high voltage,  depletion type , n channel mosfet
type numbers
LND250
LND150
C633 , Teledyne
BSP135
BSS126
DN3135
DN3145
DN3545
DN2540
BSR58 , BSR56 ?
Captured track pics for this valve preamp for deduced 
schematic for this part of the amp. some supply 
rail voltages +/-28V 

Vox AC30CC2X
Once again roadies throwing things around. Previously they managed to shear
an ECC83 in half, where they pass through the chassis "protected" by rubber
grommet. Thius time broken springline and choke bent over, by G-force, so
nearly touching the rectifier valve. Anyway the main problem was
intermittent squeel on the output with all controls at minimum.
Squeel would occur with first 2 preamp valves removed and also the
splitter/driver valve removed. I expected to find serious CH/R problem on an
EL84. Anyway all output and preamp (and rectifier ) valves test absolutely
fine on gain and CH/R over my FSD of 30 Megohm.
Replacing everything, the squeel has gone, trying the amp upside down also.
Earthing, Cs and Rs and Vs seem fine and no squeel emerges with serious
twizzle-sticking.
Assuming not a valve problem and something wrong in valvebase/ wiring /
soldering what/ where to look for something amiss that could cause a squeel
? Of course, not wanting to replace 4 x EL84 if there is a lurking problem.
I cant even swap pairs as the problem has "gone" Looks as though I'll have
to desolder the pa pcb to have a look underneath. While doing that does
anyone replace with slightly longer wires? or is that likely to introduce
oscillation problems as well.
Inject signal on white of reverb or return 1/4 in  socket 
with loop "on".
The ominous black smokey-looking splurge on the yellow kaptan tape 
of the mains transformer is underlying black tape dye 
leeching through
TT20 330V dc
Decided to use engraving tool with nylon bolt as tip and try touching bases and 
then envelopes, showed one to induce a purple flash somewhere inside and 
a bang in the audio. Replaced, assuming this one was the problem one, it 
did coincide with the same one that initially showed microphony twizzling 
the base of that one, but then disappeared.
The original wire ends of the springline were 0.15mm probably phosphor-bronze. Only similar to
hand was 0.06mm tungsten wire. To reuse the broken ferrite I had to heat up
to slide off the wire and the glue. Replacement one was an RF bead. This
spring was much closer pitch than the other 2 springs. Replacing and testing
the response at either end, compared to activating each of the other springs
(lightly sliding a toothpick along) was about 1/10 of the response.
Difference a function of the spring characteristic or the wrong metal wires
at the ends or because the this spring is in a different position in the
pickup laminations ? Presumably not due to heating as that was on only one
of them

Vox AC30 , AC30CC2X, 2005
Roadie dropped it off the stage , in flight case, worked fine for another
gig and then next time worked for 3 seconds and red LED went out so at least something 
wrong on LT prea board.
Sheared metal internal braces and choke looks decidedly drunken, almost
sheared off, but all big lumps test cold ok so far.
Fusible R188 2.2R , 1W resistor failed mechanically, not thermally, 
see tips file for case study
Someone swapped the o/p bottles with another amp and they
functioned ok in the other amp and the speakers are ok.
Replaced the failed rivets on the internal bracing with 
steel nits and bolts. 
Replaced R188 with 1W, 2.2R plus 650mA fuse and reinforced/bridged a small 
crack on the pcb. Also on prea 2x470, 2x100,3.9K, 2x C2910 
2x LND150 , 2x 2147, 2120
Readings: 17.3R mains primary
grey brown 3.6 ands 0.4R
pink .1R
purple 103R
bl. <.1R
pa 220x2 1W, 1W 10K, 50 , 82R
Choke 434R 
o/p matcher 70/72R
16R setting , no speakers, .65R, 79mH
8R , no speakers, .5R, 43mH
To avoid much cursing - cut a bit of Dexion as a 
bracket, bolt to the footswitch hole and then clamp 
the prea pcb to that while soldering the LT 
wires to the turrets. 24V ac to the prea , 95mA 
ac with no signal 

VOX AD30VT Valvetronix, 'valve/tube' amp
Went pop between songs and then no more.
Retro look of the 1960s Vox AC30 amp made probably 2004 with lots of SM
digital chippery for effects undreat of in the 60s.
One 12AX7 , but is it for show only ?
Heaters have an AC supply but the anodes don't seem have any HV components
attached to them. The speaker o/p is a non-retro National Semi LM3886T.
Poking around there are no
capacitors with greater than 50V dc working anywhere on the ps and o/p
board.
Damn hybrid O/P devices ,  -V rail to o/p short on the LM3886T, 
burnt voice coil.
Tried a 100W TDA7294 as I've a couple at hand, pinning swapped to match 
the 68W LM3886 and inverted to give some space and less wires crossing over. 
Original 	TDA pinning
1+5	13+7
2 NC
3 	14
4	15+8
5+1   -
6 -
7	4+1
8 	9+10
9	2
10	3
Ignored the bootstrap cap connection and swapping the mute line 
dropper from the -rail to the +rail.
Monitoring phones outlet all effects and classic amp colourations are functioning 
so the valve is presumably an expensive and highly inefficient indicator, 
for show only, the maximum DC on any of its pins wrt ground is -15V.
Other info
AC supplies 33,0,33 / 6 / 6.8V
DC +-43V
DC reg V 15,-15, 3.3

VOX AD30VT, 2005
Similar to the above.
Owner bought non-working thinking it was just a blown 
speaker. Replaced it and then watched the voice coil 
,through the cone, glow and burn up. The o/p device 
had been fixed back without the mica sheet.
O/p of the LM3886T about one diode drop away from +ve rail 
this time and the .47R fused.
Replaced with a TDA as above. Cut down 2 
double holed strips of veroboard to solder to 
the IC and then insulation covered wire to 
the vero. Tighten a couple of cable clips 
around the heatsink and hot-melt them to the pcb 
and remove when all completed, as the heatsink is 
not fixed to the pcb. R12 o/c so mute was 
permanently active.
For setting of Tweed,Comp,Bypass,Manual
400Hz in giving unloaded o/p at phones 
socket of .3V ac
Con 5 ribbon
DC 15,0,0.-15,0,0,0,3.3
ac , pin 5 , 1.5V
other ribbon
DC, 3.1,0,3.3,0,0,0.8,0,0,0
AC .7,.14,0,3.2,.76,.8,0,.8,.8

Warwick Sonic III amp, 2003
Nasty DC pulses into the speakers, protection circuit would cut in , relay cut 
out then back in , more bangs until switching off.
If the wiper of the gain pot looses contect then that is the result.
Disconnect prea - pa ribbon and no amp bangs
header Vs
-15,15,0,0,0
12,0,0,0,0
Beware replacing headers as not shrouded, managed to blow a fuse by 
inserting one row of pins only, misplaced by 1 row
Replaced with 470K pot and 470K wired to wiper , instead of 200K 
pot , so at least 470K is always connected to the output line.
3x IRFP9240, 2x IRF240
2x 0.1R, 5W, 6x 0.22R, 4093, 3 x 072, LM833
4.7R and 1R at zobel
fuses carry +/- 74V and 19V ac
Not the cause of the problem that it is here for repair, but I cannot return
it to the owner with this glaring potential (in both senses) fault,
presumably the same for all such Warwick amps.
One large heatsink with +75V on it and the other at -75V and 2.5mm between
the two , both mounted on standard polyester pcb with chassis standoffs well
away from the heatsinks. Discharged both before this test of course,
requires only 1.5Kg of force between the 2 heatsinks to narrow the gap to
1.5mm.
Have amp designers never seen the internals of their stuff
resonating/oscillating mounted in or on speaker cabs, especially bass amps
such as this? Fixed some paxolin in place between the heatsinks
Final checks and the fan is scraping but possible to centride mill 
back the high point in the fan surround, through the grill without taking 
the amp apart.
Someone had replaced the mute switch (dpst) with spst one leaving 
out the option of muting the line-out as well.
Normal operation the fan comes on for a second at switch on and 
then off until required. Mute signal line is conn pin nearest the 100nF 
cap on the main board.

Warwick W411PRO 4x10 speaker cab
Stored all the time, in an on the street van, and obvious mold spotting of
the cones.
Actual problem is 8//8 + 8//8 wiring with 1 driver failing unnoticed in a
gig and then  followed by the other strained one, oddly at low level output,
in practise session.
Well I assume that is the scenario.
At least I can bypass the failure pair with some high W droppers for them to
practise. 
Owner obviously handles the cabs with respect , so I have to believe that he
does not overdrive them (from the original matching bass amp ) - blurb says
600W cab
Reassembled with a number of W/W droppers in there for the
moment.
Moving the cones/feeling by hand shows no grittiness or scratchy noises so
no burst coils, no burning smells around them. There is a few Mohm across
one of them. Other than they have copious grey mold spots on the outer face
of the  the cardboard, they  and skirts etc look fine.
I hope there is a good technical reason (not known to me) why Warwick wires
them as
8//8 + 8//8
I would have wired them
(8+8) // (8+8)
so if one failed then no other failure and it would be possible to continue
to end of gig, but as driving 16 ohm, with less power.
If no one realises that only 2 of the 4 are working ,then - what the hell!
It would unlikely to be straining the amp
Horn 4.5R, 2 x3.3uF caps on xover
6R to 8 ohm over ends of pot min and max 
with speakers disconnected
1 pair of speakers in parallel 2.5R dc

Wurlitzer 200A electronic piano 1977
No sound on internal speakers and low level distorted 
sound on the jack o/p. Crackles probably due to bad solder joint 
on one of the large polyester caps.
Both soldered in 1.25 A fuses (speaker o/p) soldered to the pcb were blown.
Barrels with phosphor bronze wire wrapped around the ends
Replaced with 2 x 20mm pcb mount fuseholders but mounted 
vertically so fuses are replaceable.
Beware there is 150V on the pcb to supply the sensors.
All active components are house coded.
TI o/p trannies probably, if necessary ,replaceable with TIP3055 and TIP2955
507664-1 npn
507661-1 pnp
Working (correctly ?) into internal speakers these transistors had 
-24.4,0,-24.1 and 24.4,0,24.1V
The 14 pin IC Motorola 142349 = MC142349 ? oscillator ?
pins 1 to 14 (DC)
0,0,14.9,7.5,7.6,0 ;0,8.2,15,24.7,24.6,0,0 and low f vibrato oscillation on 
pins 10,11,12
Other trannies FMPS AD5 (ADS?) npn
Motorola 3718 pnp
Motorola 128-1 pnp
159 (TR9) npn
Motorola 144 (TR16) B-E forward voltage of 1.2V when desoldered and diode tested
Some other in circuit voltages
TR12 -.5,0,.3
TR15 .4,.9,3.1
TR16 1.7,2.8,8.3
Make sure you label near to the 2 front cover retaining screws.
"Remove vol and vibrato knobs before removing cover".
Otherwise too easy to fracture the shaft of these knobs. Reinforced 
with springs twisted onto the shafts and glued.

Yamaha CS 10 monophonic analogue synthesizer (chip dates apparently 1981 to 1986 )
Uses main chip YM 248 and also 51621,51622,51622,4588 + 2SA490,2SD235
Intermittent reduction of output level. Replaced/renovated 2 pots , 
3 switches and maintained the remainder.
Note position of case screws as 4 different types on end pieces etc. Main section 
comes away by removing 4 screws at rear. Front section hinges upward 
after removing front/under screws.

Yamaha EMX68S, 2002
Blowing mains fuse due to the all too common mid position 
short in the primary bifilar windings.
Q209/10/11/n/p 151R measured
Q11/12/13/p/n 6.9R measured

Yamaha P120  piano, 2004
Looks like another victim of lead-free solder in the power handling areas. 
Break at the power in socket.
I was surprised to see just an 8 way ribbon cable going to an 88 key, 7+
octave keyboard.
I assume there is active multiplexing hidden in there , but would there be
"touchy-feely" action monitoring as well.?
All I can see is the counterbalance rods and leaf springs per key, including
shining a torch down the length of the rear of the key bank. I suppose the
bank of counterweights (hence weight of that whole section) compared to
return springs means that touch force can be more evenly inferred from
timing intervals per key press.
Now I have it working , yes , its rate sensitive. Forte is loud.
Play a note too pianisimo and it fails to register at all, taking say 3
seconds or so from first finger touch to bottoming. I assume that is normal.
To disassemble the RH end panel does not remove, undo the rear and left end 
bolts only from underneath.
Leave LH loose and then slide the keyboard section back in and 
then slide the LH endpiece over the 2 studs via the keyhole entries. 
Beware of the bottom screening point screwed into the wood.
Component marked TH101 on overlay
In series to the DC supply to a Yamaha P120 piano , 0.1 ohm or less even
warming with a soldering iron, so not a thermistor.
It is yellow epoxy cased and about 8mm sqare like a plate capacitor
marked
HFBA CHINA
UF250 or UF25C with logo of V superimposed over an upturned V and then 3e
probably a 2.5 amp polyswitch. ?
The supply is rated 16V, 2.4A
ps remove one screw and wedge open the other end to clear the nibs. 
The cable entry protectors needed beefing up 
by cutting some heatshrink , stretching enough to 
go over the power connector and heating into the plastic vanes.
o/p board LA4705N (ps CON103)and 2x M5227
CON102 to micro board 
75C116B, 6N137 on midi board
78M12, 2 x 4570 on power in board
main board 2833, 2912, 2x 4570

Yamaha P120
Sustain pedal is just a switch sustain is o/c

Yamaha P120  piano, 2004, 22Kg
Random notes every now and then . Could not simulate but 
problem with wrenched 8 way header / socket 
to the keyboard. Partly removing the socket from 
the 1 end gives nasty noises. Disconnected the display 
gives error code 5cn . 
DC 0,5,0,0,5,3.3,5,5
pins 5 and 7 give clicks with crystal earpiece and weak 
ones on pin 6
Presumably because the right end cheek was loose and 
many screws missing underneath, along the works to move around.
machine screws are 8UNF
The end cheeks are not strong enough to be lifted by them , partially 
broke away and somehow internal wiring wrenched.
Before combining both main bits of the chassis, drill new hole for bottom 
screening earth point and hotmelt the rear captive nuts in place.
To replace the righ end cheek, push rearwards , introduce metal brackets in first, then top , 
engage pins in slots by sliding forwards then rearwards again. Next time I see one 
of these I will try the reverse at dismantling. Left end goes on last

Yamaha PSR 150
Nothing on battery or external power.
The external socket connection to pcb had unsoldered/loosened.
Resoldered and dribbled hot-melt glue to bind the socket 
housing to the pcb more firmly.The negative spring 
contact in the batttery compartment was totally corroded. 
Soldered a wire to a conical battery box spring. Led the wire 
through the existing spring soldering to the copper wire. 
Twisted wire between the new and old springs to locate and then 
enveloped in hot-melt glue.

Yamaha PSR 170, 2003
No midi output and then someone tinkered and 
ended up with corrupted notes.
Keys C , E, F and B for the first 3 1/2 octaves 
would play a note but in descending frequencies 
to the right of the keyboard.
No systematic rough/smooth cable orientation 
to the ribbon connectors ( lift to release) 
so mark before removing to avoid putting back 
the wrong way, no damage done.
The midi sockets, like all the external connctors, 
are only held by their solder pins and 
something no better than emulsion paint 
"bonding" them the the pcb. So easily 
broken. Wired in over the tracks and hot 
melt glued bodies and the other ext connectors.
To check for midi signal without a PC - 
connect both lines at the output ie output side 
of the 220 ohm resistors and monitor on 
a scope ( high with negative going pulses). 
With just a crystal earpiece , slow regular clicks 
in standby and varing rate with key(s) presses.
Uses BA5417, D2394, B1103, 2x 0.1, PC900V opto

Yamaha PSR200 keyboard
Missing notes on keys
The m/c had been used in the rain and some of 
the multiplexed tracks on the keyboard pcb had corroded away.

Yamaha PSR 282, 2001
No midi out as again nothing holding the 
sockets to the board.
The 2 long screws are in the central area near 
the battery cover.
Redid solder traces with tinned wire 
soldered in and swathed all the sockets in 
hot-melt glue.
Uses (on top boards) 2x pq05RA1, la4705n, 
3x C4570, pc900V, 29m33
Without a pc clicks on an earpiece 
on output , pattern changing with 
style and voice setting.

Yamaha RS7000 sequencer, 2001 
Popping noise like a zenon flash gun firing.
HV discharge or arcing in or around the bigger, more conventional looking of
the 2,  looks like transformer in the SMPS. 
ps marked B048 V361270
marked voltages 5, 2x 12, -12, 15, -30
Would seem to be combined effects of early example of lead-free 
solder and  clumsey roadies . The heaviest lump , 200gm, is a
double 16mH, both in series, choke in the mains feed to the HV rectifier of
the ps. 
Four current carrying corner pins to this choke have what looks like
plated through solder but now transformer is removed, looks like back to
back eyelets either side of the pcb, one inside the other and a load of
yucky solder, breaking contact in a ring between the 2 eyelets . 
2x 2.4R, 16 and 18 mH
Removed the lower cover over the pins to check nothing 
else inside , jumpered across to nearest of this 
pins , so doubled up soldering when resoldered 
to pcb and added pairs of cable-ties through holes 
drilled in the pcb.
Redid all major solder joints on the ps
short screws to flash socket and 3 to rear grey flange 
22R, 51, 56K, 56K, 180K .5W, 
2SK113
FA5311b, PC123, P41Z scr, 24A12, 7812, 7912
HA17431p (tall to92 )
With ps connected to main board , (3 connectors only 
, no added HD etc for other versions, marked C below)
measured DC on pins
12,0,12
12,0,-12, 16 c
12,0,0,5,-39
12,0,0,5
12,0,0,5
12,0,0,5 c
12,0
5,0 c

Yamaha SPX 90, 1986 , Digital Multi Effects Processor
Cold checking , have found 2 things wrong with the ps so not powered up yet
No SMPS controller IC on the ps board , a TOP66 switcher driver and 3 small
transistors.
Raw + and -18V go to main board +/-15V regulators , raw 5V , ie rectifier
off the switching transformer followed by one L and one C goes straight to
the 5V TTL rail. Not even an obvious fat 5V zener across it.
No SMPS controller IC , that I can see on the main board and the 2 lines
from the main board marked PE and PC that go to the mains side of the ps via
opto isolator .
There are 15 assorted wirewound resistors on this ps , again rather odd.
If I get it working , a ventillation hole and grill cut in the top cover
would help.
It was that hand over period ,  80s , when phenolic pcbs went over to
polyester.
This Yamaha has polyester main board and phenolic light brown ps pcb that
has a lot of heat dark browned/brittlised? areas. Not surprising with
assorted 15 W/W plus sm driver etc with no ventilation holes anywhere.
Got it back to working to its earlier non-working condition before it was
seriously
mangled by a "repairman".
Can now see that the original problem was an 85 dec C electro that did not
like being cooked in there.
I determined the schematic for this SMPS
The 5V regulation, unlike the +/-15V, is on the ps itself, in discrete form,
consisting of 300mW zener,preset and TO92 transistor.
Working at 2/3 mains coltage but temp of the chopper transistor goes too
high, if I let it, and power consumption goes well above 20W.
Looks as though something has gone wrong with the mark/space control.
It slowly increases so the "5V" line goes 2...3V and then jumps to 5V with
equal mark/space which is presumably not necessary.
I checked there is no excessive load on the +/-18V or 5V rails despite
all functions working as far as front panel display.
To get a rough idea of the amperage capability of a small 5V SM ps
before attaching it to its load, to simulate, just in case the regulation is
kapput.
 It uses a TOP66 of sufficient rating to
drive a few hundred watts across but the ps is relatively low power , but
unknown rating.
The one in question is only about 20mm cube
I've fathomed out how the ps works. The 5V regulator uses only a 100mA TO92
transistor because the error is fed forward via an optocoupler to the sm
oscillator.
The 5V line defines the output to +/-18V as well.
The original trouble was wavering 5V, which has returned, prior to replacing
some more caps . In the broken mode if say 2.5V on the 5V o/p then only
+/-10V on the unloaded +/-18V lines.
Scaling linearly, an at hand 70 W  smps, with its 45mm cube transformer.
I would estimate volume for vol then this one with 20mm cube would be about
6W total. Allowing 1W for the few op-amp supplies and 2 relays then only 1
amp at 5V, its suppling 30 odd 74HC and 3 LSI.
When operating properly the oscillation is about 59 KHz with equal
mark/space ratio,
when at half-cock then about 40KHz short mark/ space
The consumption plate states 20W, assuming average SMPS 70 percent
efficiency then 14W at DC.
uses 2SC2792, 2SC2634 /2034?, 68uF/400V, 2x 1R FR
3 x 100K w/w ,6.8,2x 68K,22,2x 330, 2x 120K, 6.8, 1.5, 22, 27
2 fuses marked micron63 FN191R0J
6.8,100R on main board
The second optocoupler is the other way round.
Feeding rectified but unsmoothed mains signal info to the main board.
Phase info for mains hum/noise reduction?
6.2V zener on ps for 5V regulation section.
In working order but short duration of 65 percent mains 
load was 85mA on -18V line, 128mA on +18V, and 360mA on 5V 
so 5.6W (placing 0.5Rs and 0Rs between plugs and sockets)
At 70 percent mains was getting 2.5V on '5V' and -10.5V on '18V' slowly 
building up to 5V, feeds forward via pc1.
Replaced main chopper transistor, D1207, 2x6,8 to 12R, 2x 330 to 2x1000, 22 to 68 
and 1.2K 1/3 watt setting chopper bias to 390R and unnecessarily replaced PC511 just 
in case.

Yamaha Stagepas 300 miniature 8 ch mixer amp
Only 2.5 Kg weight and 10x6x 2.5 inches, 70W consumption ?, probably made 2005
intermittent then no left channel (no pan control on 
this amp so L-R a bit specious), 150W per channel 
in the blurb. Speakers measure 5.6 ohm so 
probably 8 ohm.
Not possible to play around with it without disassembling as, all wrapped
inside one another.
Marked all the bits of celluloid and sub-assemblies before disassembling.
No obvious solder problems or wobbly bits under illuminated mag glass.
The power board with 2 fans is confusing because what looks like 2 channel
power amp farthest from the mains inlet filter chokes is a very distributed
SMPS, split into 2, especially with a thermistor on a vaned heatsink with a
7 pin TO220 device either side, that look like TDA... monolithic audio o/p
blocks.
But those devices are TOP249YN smps drivers.
The compact lump nearest the mains inlet, that looks like a compact SMPS,
contains 4 TO220 devices , ST P14NF12FP 120V 14A mosfets.
Generally i would say this was well constructed except for the conical
greyish silver solder points. Perhaps 1Kg of the overall 2.5Kg is the weight
of the thick steel top fascia plate and the robust black enclosure box of
composite/plastic/rubber or whatever thick and dense formulation.
One potential problem, is all the pots are pcb mount only with
no bush nuts to that nice steel fascia, i've checked the dual master one
with DVM but seems ok.
I don't know what the electrical/electronic term is but in nuclear power -
the "void coefficient " could be a problem. 2 fans , 1 1.5 inch and the
other 2 inch . If either of those stopped with all that power consumption in
a small space , I wonder what the result would be. Hopefully the thermistor
would initiate a shut-down procedure.
Because of the coil blocking removal of the bolt 
through each pa heatsink. To remove the mosfets desolder the nut 
side one, slackening  off 
the bolt enough to de-solder the heatsink and then remove 
the other mosfet. My replacement were not insulated so 
the mounting hole through the heatsink needed enlarging to 
take a full depth insulating bush as well as mica. 
Class D, but not unipolar design, and 2 
"channels" of SMPS for + &-
2 neatly shorted D-S-G mosfets and 2 neatly o/c 0.056 ohm wide SM resistors
leading to each of the o/p filter electrolytics, no overheating, charring or
burning anywhere.
So assuming no leads to speaker or speaker problems what would cause this ?
I had previously desoldered one of the o/p electrolytics on the other more
accessible board to try and read the ident of the obscured mosfets and that
cap presumably only had marginal soldered contact via junk lead-free solder,
could that be a cause? the 2 off per channel 50V, 470uF HF filter caps
across the output.
http://www.diversed.fsnet.co.uk/solder.jpg
Here is a pic I took of what was probably tin pest.
Ignore the top pic as just a control showing normal silvery appearance of
pins after desoldering.
The black cap, the top pin could be pulled out and the bottom one needed
desoldering. It is just about possible to see the all grey dusty covering to
the top pin. So that 100 percent tin layer eventually turns to the grey form
, expanding in the process. So like a weed growing through concrete it
forces the solder apart as well as in itself being non-condusctive.
The solder joints on the caps and elsewhere 
otherwise looked normal, only this surface layer tinning of the pin had
transformed to grey.
Located down to one of the power amps, permanent out rather than
intermittant now, nothing found twizzling.  Both have indirect edge connector pairs . It
would be nice to swap them over because the duff one is not very accessible
without making a pair of extenders, but probably not advisable, 
as maybe not identical, the feeds are different.
With maybe 250KHz on these amps in operation I'm loathe to put a scope
around the mosfets and will try and diagnose cold.
find space on or off both pa to replace the 50V 470uF
pairs with something higher than 50V. They are part of the LC LP filter
straight across the output via the o/c Rs. As there is nothing wrong with
the speakers or leads then internal punch across these downstream of mosfet
electrolytics (test to 60V ok) is likely reason for blowing the 0.056 ohm
resistors on the outputs and then blown mosfets.
Can anyone explain this
"Yamaha STAGEPAS 300 description:
8-channel (4 mono & 2 stereo) powered mixer removable from its host speaker
(mic stand mountable)
 2 x 150W class D power amplifiers"
from advertising blurb.
Each pa module has 100W marked on it and the mains voltage detail near the
IEC socket says 70W .
These class D amp modules are not unipolar.
On 60% mains or full mains it has + and - 38V smps rail supplies.
I replaced each of the 470uF,50V with 2 seriesed 1000uF,25V, so much bigger
volume than the tiny 15mm long, 12mm diameter originals, but just 
room inside the case , wrapped in shrink-sleeve 
and placed over the regulators . The blown Rs replaced with 7mm long 
pieces of 8 ohm per metre constan resistance wire. If the other pa 
had blown there would not have been any space for larger caps.
But it is now working
with a pair of mica backed IRF740 instead of the fairly expensive proper
mosfets that seem to have only one supplier in the UK. With no undue heating
at low power, bit higher RDSon etc. Its a matter of desoldering 
the devices and the heatsink for removing because of constricted 
access to the through bolt.
Very strange having a whole amplifier weighing only 60 gm but the advantage
is they easily unplug and can easily power up off a bench supply. So using
+&-30V I noted what the standing DCs are around the mosfets, no sign of any
oscillation, I assume the oscillator is taken from the SMPS oscillator to
avoid beats problems if free ruinning. Will have to remount in case for
proper airflow before full power testing, whatever that is, 35W, 100W or
150W each channel. I managed to replace one cap the wrong way round 
causing severe heating in the cap naturally and the ps cycling on and 
off due to excess current.
Right channel ok, on main power board 200+ numbering, pin 2 from the mixer 
board left channel was blown, numbers 100+, pin 1 from the mixer board
pa
CN3/CN7 pins
1/ gnd
2/ electro to ground / to CN19(2)
3/ i/p via electro / to gnd via electro
4,5,6/ ground
7,8,9 / o/p
CN4/CN6
1/ crosslink to CN6 (oscillator feeds?)
2/ ditto
3/to Q806 2sc2026 / -ve rail on CN6
4/ gnd
5,6 / C828/9, -ve rail
7,8 / C812,C806, + rail
With disconnected power amp powered from a dual 
30V bench supply, only, no external oscillator
settles to 0.7mA consumption with supply 
of +29.9V and -29.8V
standing voltages on the 2 mosfets
G -1.22,D 29.9, S -1.57 (drain via 0,056 to large cap)
S -29.7, D -1.57, G -29.3 V (source via 0.056 to large cap)
first S and other D joined and via transformer to the output. 
other parts
JRC 2068D op amps, M6580fp echo delay
large thermistor 8 ohm cold, small 65R cold
15, 2x560,2x1.8K,2.2K,4x27K large Rs
3x p42 optocouplers
78M06, 8715A,7915pi, 10DL2CZ double rectifiers
400Hz source sine fed into one amp only, delivering 12.5 watts continuously
into an external dummy load. After 40 minutes the exhaust temperature was
still increasing but very slowly, so cancelled then. So heat from 2 switch
mode power supplies and one idle amp with no load and the other one active
plus contributions from the voltage regulators and mixer circuitry etc.
Temperature from bulb of thermometer laying directly over the exhaust vent
rose to 42 degrees C from a room temp of 24 degrees C.
With the owner putting a thermometer at the output 
for an hour of normal use it only rose to 30 degrees.
The reported hot venting was only prior to the 
ultimate failure and was not normal.
It is possible that there was ultrasonic oscillation 
prior to failure.
Measuring the output airflow into a thin plastic 
rubbish sack for 3 minutes until 2/3 full , measuring 
exactly the volume then the flow came to only 0.78 cubic 
feet per minute.
Using vol of air per min = watts / (air density*specific heat*temp diff*60)
in metric terms
60 seconds in minute , taking air density = 1.205, Cp= 1.05 and conversion
factor of 35.3 for cu m /min to cf/m and measured outflow of 0.78 cf/m ,
however I plug these measured results in,scaling for higher demand, does not
look good for temp diff at higher output and fan duress apart from the
electronics which could be in circulation dead spots. 
It would probab;y be sensible to bend up the output 
vent anchored with a standoff at the fixing screw and a bit of 
filter.

Zoom Rhythmtrak RT 234, 1998
nothing 
pass transistor , SM marked CG GH failed
replaced with full size BD132 placed on edge between the caps
"space bar" is used in conjunction with keys as a repeat.

Zoom Rhythmtrak RT 323 drum synth, 2002
Bad output connections
Resoldered with much more solder all the rear joints, 
the power socket could of gone the same way at any time 
and the rotary pots done also.

Zoom Rhythmtrak RT 323 drum synth, 2001
As the other one, bad solder.
Added 2 bright white LEDs running at 25mA each to 
illuminate the LCD. Top and either side of LCD, angled diagonally. 
Remaining edges of LCD glass and the surrounding well 
coated in Tippex to reflect light.
If loss of key actions and scratchy noise from 
song play. Pins in region of pin1 (N/C itself) and 
opposite side having bad contact to pcb of IC17 
marked Zoom 234-1001 and 0124K7001.

Diverse Devices,Southampton,England


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,
schematics etc)
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.


e-mail 
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More hints & tips and repair briefs on
homepage http://home.graffiti.net/diverse:graffiti.net/