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Band Amps and other stage gear , A to M
AER Compact 60, made 2000 German made very expensive 60W "practise amp" but well liked for its features. The owner's cat , not a tomcat fortunately, decided to piss on the cabinet. Piss went down inside the Neutrik XLR/0.25 inch socket and also corroded the gain pot so it stiffened up too much to turn properly. Easy enough to desolder the pot, clean and ream out the aluminium corrosion. The neutrik was a different matter, could use the XLR input but not the 1/4 inch, horrible blue-green mess of corrossion inside after desoldering and prizing off the rear. Cleaned out the worst with meths but could only return to normal use by removing the grounding contact that lodges in the rear closure, it would not cleanly make or break and as had been used for months without , in effect, the grounding due to corrosion. As a pin for pin replacement not available in the UK. pinning arangement (I've labelled the A,B,C as not on overlay) A B C 2 3 1 SS R S G B,C,1,R,SS,S were all grounded with no plug 2 to ground 1/4 inch S=gnd, A=tip,R=ring no plug R to gnd Also fixed the rather crass foam cover in place with strips of double-sided carpet tape. Technical notes Large Rs 2 x 82, 5W TDA7294, 7815,7915, 2x 7805 33078 opamps, LF353 SSM2142, 470R, SSM2018,LM393,TL072 3x W24257aj-12, HC02A, HC123A,HCT05, AD SD 2115, CS4220 TL072,HCT14 and in all the amp just one tranny K30A incidently "diode" DVM test readings for a good TDA7294V relative to the heatsink 1,3,5,7,9,13,15 .6,.6,-,.55,.6,-,.48,1.2 2,4,6,8,10,12,14 .58,.58,.55,0,.6,-,.49 Akai AMX10 mixer amp, 1999 Dropped then nothing. Surprisingly the latched connector between IEC socket and ps had disconnected, large toroid filter broken away from pcb barely held on by two wires and a crystal problem on the mixer board. ps and amp uses K1181,2x K1179, .15,.22,47K,LT1509 6x 1k, 4x W38NB20, 47k,3x 1M 7915,7815,24M05,7812,78M24, 4x .47,22k 18,10,18,470 ribbon to mixer 5,0,0,0,0,0,5,48,-15,0,15 Alto L12 mixer, only 2007, not 2 years old Intermittant loss of one channel , in different positions of the master slider. Undo handles and side plates. Remove the knobs of pots and sliders only, not bush nuts. Undo the 3 front and rear screws that hold top to bottom of case. Break off, with pliers, the hot melt from the headers. Undo the 14 screws from the top, not pcb side of spacers, to remove the main pcb. Beware the trick one under the graphic slider panel, threaded stud so may undo. Remove the main pcb from the panel at the end with the 2 small ribbon connects , first. End-snipping and then grinding off the tinplate tangs before desoldering the active pins is the way to deal with these tiny sliders , without colateral damage. Getting inside, the non-resistive tracks are only 1mm wide and one pair of single wiper "wires" must have been right on the edge of one such track so intermittant contact, 1/2mm transverse bend and repaired. Will resolder the remnant tinplate tangs for earthing and add hot-melt around the housing where there is spaces. 4 tracks inside the 8mm width and 1mm for the conductive track and very easy for the pair of wiper contacts can veer off track. All 9 of these sliders are the same, but no problem with a channel one going U/S unless someone uses all channels, problem was of course, Murphy's law, on the critical one. ps voltages printed on the overlay. Ampeg B1, 1992 Blown transformer due to shorted op device and TIP device broken pull switch spindles repaired as PTF. 2x MJ15001, 2x MJ15002, TIP31C, TIP32C, 2N3402, 2N3440 220R, 10R, 3.3R 2x 10R, 100R, 2x 1K, 4x 0.33R 24V fan N/C th sw 2x 5532 Arion (Prince Tsushinkogyo) guitar tuner,1985 Not chromatic (new one on me) ie not full spectrum , does not have pitches "C" and "F" , dedicated to guitar use. Bad on/off, probably lead/jack trodden on and broken solder on socket joints, no nut mechanical holding of the bushes through casing Ashdown ABM500 bass amp, 1997 Farty noises Had been seriously dropped in a flight case and a number of problems, now sorted so it now works but there is a fairly low level background hum problem with no input. Attending to all the pots as most were worn or suspect in some way and some solderings at the heatsink. schematic from Ashdown Festoon bulb replaced with a physically larger 12 V bulb so mount needed extra fixing in place, o/c voltage supply, has dropper, at the bulb mount 17V ac. Some other data secondaries 13.5V; 62,0,62 ; 17,0,17 ; 270V (16 ohm DC ) main ps , +/- 84V Thermal sw n/c. 1V dc over meter reads "2". At 22 deg C , the heatsink thermistor , in circuit, measured 70 ohms giving only 9.6V at the fans, parallel with 68R gave 11V and 28R // gave 12.3V. To remove the preamp board, remove pot and switch knobs and push in switches and slacken off the transformer to give space. Shift the other way to remove the rear board. See tips files for coachbolt removal problem. All inputs and outputs and pots (exept the pot casing) are electrically isolated from chassis, on schema and in reality. Just the mains inlet earth bond point to the chassis. The pa has a nominal "grounding" point of // 100nF + 10K, 1/3W R and the pre has the same to chassis and the signal line "ground" between them. Another sort of problem with this faux ground arangement. I thought it odd how long it took to drain the 450V caps and the main reservoir caps, before I previously dismantled all the boards. You have to connect the low ohm resistor to faux ground rather than through 20 say + 10k//10K to real ground. So about 5K between real ground and nominal ground. Disconnecting the signal lead, the pa o/p is clean. Driving into 8 ohms , with shorted inputs then at max volume setting then 0.7V on DVM ac range, dropping to 0.002 V for min vol. It is more intrusive than I would normally expect but I don't have any figures for what is normal. shorting the preamp 10K then the hum goes. The input 1/4 ins shorting contacts, with no input jack, are ok Putting 1K across the pre amp 10K then the hum level drops to a much more acceptable 0.1V. What are the safety issues with this sort of arrangement ? They are not marked on the schema as fuseable resitors nor on board marked ! in a triangle. I've probably found the source of generic hum noise problems in Ashdown amps with this faux ground structure. The problem pot marked with a "B" meant it was linear and not log so a replacement easily found. Taking the original apart there was no broken track or rivet /paxolin failure, stressing/bending paxolin and measuring etc showed nothing untoward. But I did notice the track was offset, ie not coaxial to the paxolin base. The noise intrusion was most prominent at about 2/3 and at that point due to the off centre track and slight ovalling of the outer pot casing the track/wiper at this point was very close to the casing. For the replacement pot I bent back the four tangs that hold the middle casing/housing section of the pot to the bushing plate, introduced four bits of insulation, closed back on them and glued in place. So the casing is now isolated from the spindle and bush which is still properly grounded to the chassis. Now normal hum level with shorted input and maximum vol/gain settings varying from .04V clean to 0.07V ac on full grind setting into 8 ohms. So factor of 10 or better improvement just from isolating that one pot casing and presumably more centrally aligned pot tracks perhaps to lesser effect. The 2 x 10K faux to ground resistors still as the original design. One of those annoying self-made, in a sense, problems also associated with the faux earth. Trying the amp with the equalisation board free of the chassis was fine but mount it back in and horrible mains noises. To save messing about I was temprarily placing the board back in without the 3 spacers on the 3 pots. These pots have the casing to chassis earth but the 4 slider pots have the cases connected to faux earth. Without the spacers then the slider cases came too close to the chassis. The grid vltage on the ECC83 varies from 0 to -3.8V via the clean/grind pot I wish there was a proper techie/muso translator somewhere ,ie full translator techie-speak for techies and muso-speak for musos . What is grind ? in terms you can see on an oscilloscope for instance, not the usual muso speak. I want to know, in this instance, if you feed say a triangle wave in what comes out on full grind? Final loading check , 400Hz, giving 20W in 4 ohms, no rise or drop in Vac over test period. Heatsink with the 2 fans active gave 20 deg C rise over ambient of 22 in 12 minutes. Also into 4 ohms, no input , clean channel full vol & gain of 0.03V ac of mains hum over the load Ashdown ABM-500 EVO-II Head, 2002 Intermittant cracles and gain dropping, part into a set with normal usage. 2 temp sensing things , one vaguely touching , the other bent away from the heatsink. Perhaps every roadie should be put in a flight case and dropped down some stairs as a lesson. Anyway both heatsinks must have bent relative to the pa pcb, bending the leads , when dropped. Main spring held items stayed ok. How to anchor back more firmly than just white paste? The main TOP66 power devices etc have those slide on spring steel clips but the loosened TO92 tranny and fan thermistor are a long way down from the mounting slots, for anything like that. Any ideas ? - live heatsink btw, hence not rigidly held to body. Too crowded to drill/tap the heatsinks and the assembly of these sort of hook-clip arrangements is realy make once, dissamble/reassemble at your peril. This is a likely generic fault scenario for all such "live heatsink" amps that are only fixed to flexible polyester pcb board Double sided foam/tape tape was supposed to be keeping a duaghter board marked EB SUB ? (not on the Ashdown supplied schema, 4013 and 3 x 072) fixed to the preamp but dislodged in the same drop presumably, failed solder joint/s leading to crackles. I removed 2 nearby caps , 2 small holes ,to match cap pin spacing, in cut down lengths of cable-tie , and soldered back in, regooing and positioning the 2 shiftees. Volume was fading down after half hour of use, presumably because the NTC fan thermistor was staying at room temp and fan speed not upping with increasing heatsink temp. Unsupported daughterboard is now braced back to 2 chassis anchors NTC thermistor TH1 ,88 ohm cold 2.2K,4.7K, 1W, 4R7 vitreous 33R , 1W on prea board main bridge rect , one prong poor solder, supply pcb conn block for fan , bad solder. Ashdown Electric Blue 180, made 2004, 26Kg The amp cut out totally and when it had cooled down and he switched it on , it worked, but he noticed the fan was not turning so he switched it off again. Beware the heatsinks are not grounded and +61V on one and -61V on the other. The supply to the 12V fan is off the preamp board so had to remove from the front pannel. The owner had never had to tighten any knobs but one grub screw (brass) had been graunched at manufacture so had to drill that out first (see the tips files for technique). The 100 ohm dropper to the fan had resonated and failed inside the pcb hole, copper coloured fracture face so presumably work hardened copper failure. 150 ohm dropper in the display area had overheated to 156 ohm and giving apparent band colours of brown black black. Uses 2SA1668 , 2SC4382 2068, LB1443, 5x TL072, M51134FP 2x .33, 4.7, 4.7K large Rs Speaker DC resistance 5.6R Ashdown MAG 200, maybe 2000 or 2002 schematic available via email from www.ashdownmusic.com/tech/schematics.asp Combo with 1 x 15 inch speaker. After hour of use it cut out. Next time it failed after 10 minutes. Lead-free solder "volcanoes" or electrolyte from the 10uF cap near the J112A N-D type FET caused solder failure on the cap and falsely triggering the protection circuit. In use voltages on the 112A were 0.2,0,-8V clicks over at about -1V As mosfet discharge the reservoir caps before dismantling if no speaker load. In working order the Source to ground of each power fet shows a forward "Vbe" one way or the other and only that terminal. To get to the front board leave the 4 nuts in place and remover the 2 captive nuts and the 2 small screws on the top. To replace put the sleeves into the front panel rather than on the pot shafts and locate the meter into recess before pushing in the pots and switches and sockets. The thermal switch T'-key 125-a15 code meaning 125 degree C, I took to 120 C and did not change state and not mechanically suspect. Also 3 of the pots were (needlessly) long shaft with nothing other than paxolin and nylon bearer around shaft keeping them in place. Could easily have used the normal shaft ones and extend the pins, so proper bush nuts to front panel could be used. Replaced with a panel mounted one , wired into the board. Meter had been pressed in and soon would have had solder joint broken. Made a hole through the pcb for a nylon bolt and nut glued to the component side of the board so could be tightened against the meter when aligned and fixed in the chassis. I do not know if this is correct setting but this VU meter was 0 on scale with 0.18V RMS 1KHz input from a 600 ohm source and input pot at maximum. I don't know what the illuminated meter looked like as original but I reckon my re-jig would be better, looks quite nifty, although not 'retro'.
Because the cover protrudes 1mm or so it even looks effective skew-on. Put a 2K , 3W dropper in and a bright blue LED wired-in and moved to vertically under the meter movement when mounted in chassis and angled toward the ring section, so internal refraction , through the plastic, forms a blue ring around the ali cut out , especially after abraiding the coating off the aluminium in that recess, plus a bright spot under the meter that shows in bright ambient light and it also throws a light on the scale. Filed a small notch angled downward so the front periphery to the meter was still circular but allowed more light into the bottom area of meter cover, revealing more of the LED directly as an indicator for bright light conditions. 2 LEDs , under but angled in and across, would have been better as the static part of the movement shadows part of the light cast. Comment on return to the owner. "looks amazing! thanks for doing that, it really makes it stand out, cheers" The 20mm fuse on the preamp board is too close to the metal edge so covered with a cut-down piece of wide flatted-U file binding spine. As all lead-free solder redid all heatsinking joints on both boards.Main AC rails 50-0-50 and preamp 18-0-18. Ashdown MAG 250 For factory retro-fitted fans. 4 faults in one just fitting a fan and power bleedoff For random fan stoppage - look for Instead of 47R 5W W/W placed in line with the fan (dangling R unsupported at one end) , 0.047R soldered-in so 21V across the 12V fan. Surprisingly thousands of hours of unproblematic use like that. Even without that , for any long term excessive wear on the bearing of fan , the reaction force pushes the impeller towards the mounting bracket, eventually touching it. You could see a slight trace of where one fan vane had rubbed the bracket and rubbed the plastic of that vane, ie clear of usual gunge. If meter cover stays in fascia cover to protect when working on prea. Replace with 47R, supported by tagstrip bolted to fan, and new fan with the centre section of the mounting bracket hacksawed out. Take negative lead via a wire to an added terminal set in the prea. Fourth mistake : the fan just circulates the air internally, no added baffles to duct air in from outside. Set the fan in a stiffened card bafle going from LH corner of front to centre divider of rear vent. So air heats up, softens fan's plastic vanes , vanes flex a bit, to the extent of touching the mount. Removed the the sw and checked for temp action and any vibration sensitivity and checked caps in the controller area. If the sw goes o/c in these Ashdowns the gain drops at the top end mainly, not cut out . 1KHz in and 1V ac over dummy load then if sw changes then o/p drops to 0.04V ac, less so for lower frequencies which seems upside down for amp protection. Still random intermittant gain drop and distortion. Beefed up return socket switch as per tips. The holes and pads for these are far too big for the pins so a good place to see crcked solder, but not this one, so far. R46 , 1/3W, resitor at the 1.6K bias R cold joint. Ashdown MAG 300, 2004 pcb marked MAG250 EB150 Blows mains fuses during low volume practise session. Survives long enough for the meter lamp to come on half a second. Nothing found obviously suspect in ps or pa probing around cold and inspection. Bad internal AC supply fuse holder contacts , arcing burn marks on the fuse barrels. Both are 5 amp rating but neither blown or showing stress on the fusewire. So much for so called "Top Cheers" transformers. Initially could take variac to 50V and then run away , now cannot even put the minimum of 5V on the primary , with nothing connected to the secondaries. So just coincidence of bad fuse holders on the 48V ac lines or directly leading to failure ? Could repeated breaking of secondary current induce very high voltage in the primary leading to shorted turns? Nothing visibly wrong through the tape wrap or smoke trails from inside. DC measurement on primary now about 1 ohm , unpowered, was about 6 ohm when received. The first winding was the low current 15-0-15V secondary. This was wound with doubled up .45mm wire in one go so reducing the number of shuttle passes to wind on. The 2 wires brought together to form the "0". Thought to myself, perhaps that is ok for low voltage winding as only 50V peak or so maximum for 2 thicknesses of lacquer to sustain. Then the 3 amp 48-0-48 wound as 2 separate layers of 1.06mm wire, not run as paired winding, fair enough. Anyone know why 3 runs of loosely packed turns per layer when one run of tighter turns per layer could have been done, so avoiding overlaps? Get down to the unruptured thermal fuse, tails of the primary and the .7mm wire primary and nothing obviously wrong in the way of hot spots. But blow-me-down a return to the paired up winding and ends joined to give 120-0-120V for 240 UK use. But of course now 2 thicknesses of lacquer having to sustain a normal maximum differential of about 350 volts. Totally wound off and the small burn patch was midway , where maximum voltage difference is/was, so just required some otherwise rather minor, short duration, mains voltage spike to puncture through. Thermal fuse marked 17 AM 033A5 M4 AB if anyone knows what that means as temperature. speaker 5.6R Difference on cold probing between drivers on both sides of the amp due to resistance 47 + 330R between B-E of C4387/ A1668 but not corresponding ones. If gingerly powering up this sort of amp don't have a speaker connected as amp is unbalanced below about +/-25V. Powering up on bench power supply and monitoring output line +/- 10V o/p 9.9V +/-15 o/p 12V +/-20V o/p 18V +/-25V o/p settles at 0V Uses +/-70V 2x 2SA1294 , 2SC3263 Output pot goes past the endstops, dismantled and reformed the outer case. Meter on this ashdown stuck at the top, needed desoldering off the pcb, measured 650R and read 80 percent on DVM voltage, unstick the tape before resoldering. Mag 300 No output after someone replacing the fan and not discharging the main power rails at the o/p device heatsinks. Touched one of the fins to the prea -ve power rail. Shorted the -15V zener and at least one of the 072 IC2 / IC3 . As received static 0.43V over the meter . Replaced the zener but problem with the bass pot so that above 1/2 then distortion and then cut off. -11V on pins of the ICs that should be about 0V and varying DC on the tone pots. Ashdown Peacemaker 20, 2003 Loss of preamp, pa ok with external feed 0.05V 400Hz ac into return produced 3V ac over 8R , "maximum " volume set. Signal injecting at pin 6 of IC2 and IC3 produced o/p 10K dropper failed in valve anode supplies. No obvious reason for failure , even breaking open, no overheating or colour change to body or bands . Replaced R11 and R23 also o/p tx 0.9R R90 22K replaced with 2x 47K , 10K in the schematic and A1=A2? To refit main board , and 1/4 socket spacers, 3 each to the front and 2 each to the rear Ashdown Peacemaker P60 valve combo, 2003 Volume fluctuation and background rustle I discovered how to get into it, remove front knobs etc and remove the facia panel first. Lever out the mains switch enough to pull the fascia around it. Remove and replace amp with cab on its side. Meter unslots and tape it to the underside of the chassis. This amp runs very hot in the region of the EL34 output valves, almost to the point of charring the pcb, localised black rather than just brown discolouration, through the bulk. The valves are inverted and no ventillation path under or around the valve bases. There is plenty of space to mill holes in the pcb around the periphery, and avoiding traces, to allow some ventilltion through. Scraping back some of the pcb surface browning and into the bulk of the pcb material , the browning extends the depth of the material. Also some brown staining on the surface of nearby solder points, probably some vapour coming off the polyester and settling on the solder. No ventillation grill in the cabinet top either. I'd half considered a fan but there is no obvious place to put it and without cutting a hole in the steel chassis or the wood cabinet it would just be circulating the air, unless mounted outside the chassis , directed over the bottles. Could use the rectified heater supply as a less than 12V supply for a fan. Cut a 3 x 2 inch hole in the cab top , masked with grill. Positioning it asymmetrically off-centre in both senses so above the big bottles and clear of internal encumberances so a 2 inch fan could be fixed under the grill , later, if required. Bolted down some metal bar etc with the handle bolts to form a slideway, for 45 degree drill bit guide to slide and step along to cut 2 angled slots to bring the vent hole inside the cghhassis. Cut through the ends and tidied up and painted black. And the pcb perforations with dremmel and 1/8 inch ball mill Putting a thermometer in the quiescent vent flow, 40 degrees C above ambient, better out than in. On EL34 side of one AC coupling cap .25V ac dropping to about 0V and on the other side .25V upping to .3V on volume drop. Replaced that one nearest the heat build up and its match. The pair of 220K in blacked glass sleeving to -12V is to " stablize the bias until the tubes have warmed up enough for the self-bias to take over. It adds about -6 volts to the grids" soon after switch on. One HT cap had bad solder. Replaced weak input socket. Beware earth continuity is through 1 only pcb standoff and beware of trappping loose wies against standoffs. EL34s use ac on heaters, 12AX7 s use +/- 12V DC in pairs 33K large dropper, bad solder points and overheating, stood off the board with heavy duty pins, also 2x 1K, 2x100R, 1K. 2 canted 072 because of large Cs. Mains 7R // 29.5R,.2/.3R,.3R o/p 113R bn, 103 bk,// be/gn .9R, Y/W .3R with o/p set to 8R Not returned in 4 months of use with passive venting mod, for fan retro-fitting, so presumably my venting mod was enough. From a USA user "I came across a thread on cooling issues with an Ashdown Peacemaker I bought a Peacemaker 40 in the US. I have experienced issues after a few hours of having the amp on. At one point I use to put a window fan behind the amp while we played! I thought about mounting a fan as well but I would prefer not to cut a hole in the outer cabinet if possible." Ashton GA80 guitar amp (Australia) RoHS date of introduction for Australia ? Anyway 1/4 inch i/p socket too weak even for domestic use , breaking up in a few years ( within RoHS regime), no obvious datecodes except main electros seem to be 2000, otherwise maybe 2004 or 2005 IC dates. No-name flimsey junk , the type with 2 insulated change over contacts. On trying to work out the functions, apart from the tip contact/grounding setup there is a line to one of the isolated switches that grounds at plug inserted and o/c when removed , it goes DC connected to the base of a pnp SM1015 transitor - function ? If it kills the gain for bang-less plug insertion then it would only work for insertion , not removal, as that switch makes before tip makes/breaks ground Luckily the owner wanted a reliable input socket and was unconcerned about the loss of the plug-in de-thump cct. To replace the domestic headphone socket (has isolated switching) would have been a work up as 0 or 15V on that control line so could not use an effects pedal type ring switch action. And the ring switch for a normal stereo 1/4 inch jack is the wrong action for here anyway, requiring an inverter somewhere or one of those awkward and rare offset 1/4 inch switch actions. cct proper, holds off full gain for 0.5 seconds or so after plug insertion, all the while removed 30dB or more gain drop via 15/-15V control into the first amp. Although no obvious PbF solder problems the original input socket had thin+wide blade pins going into holes of that wide diameter and loads of filler solder, asking for problems with ordinary solder let alone new-fangled More as a reminder to myself, for the next time this problem appears. A work around without having to cut into the existing cct to put in an inverter. Use a small SPDT relay (+emf diode) with power adapted from whatever convenient rail. Permanent ground on the flexing ring contact in a 1/4 inch TRS socket and the fixed ring- contact to the low side of the relay. The added delay, due to relay action, only adding to the desired effect of delaying the removal of the gain suppression until after tip contact is made ( unless someone is very slow at plug-in) Uses 2SA1941 ,2SC5198 2K7,10,100,2x .22 A1837,C4793 7815 , 7915 ? not seen 220R for phones 34-0-34V ac 19-0-16V ac That SM1015 base goes from 14V to 14.6V in each state and Col 14.7V to -14.8V springline 27R,215R Audition spring-line amp Excessive white noise. Germanium technology low power practise amp one time sold at Woolworths with detacheable 15W speaker.Replace the input side transistor 2SB440. Big Time practise amp failed mains fuse assembly uses D1406 and B1366 , 2x 0.5R, 4559 Boss DD3 digital delay foot pedal, version 3B , 2003 ? Does not always latch on, momentary footswitch seems ok eg physical switchpoint, zero ohms on , the latching is via RC and taking an input to a 74HC00 low. Mark all the 1/4 sockets before removing as their orientations are critical. Original problem was probably (from sooting/tiny etch mark) the electro (too long lead had touched the adjascent ground line so cut it back)at the 5V line of the SM 5V regulator marked "A E" , IC9 I don't like the indirect footswitch ground line via 2x 1/4 inch sockets and casing but nothing loose. placing various Cs across the sw made no improvemnt. Desolder the small pcb off the switch so the metal casing can be removed for ease of working on after demounting the sockets and pot board. Did a subcircuit determination Using one wasted, as paired-up, input to one of the SM 74HC00 gates , cutting just one pcb trace and added an R,a C and a D constructed a 0.4s monostable, pulse stretcher so now latching properly. It does not seem to have affected the hold mode option either. Footswitch goes to ground to activate, with input lead connected. via 100 ohm to pin 1 of 74HC00, linked to 2 (H via 100K), 3 to 4, 4 to 12 and 13 and red lead to hold option on mode sw, 5 (H via 100K), 6 via 10K to pin 62 of main IC, 8 to pin 59 of main IC, 9 to brown lead and hold option on mode sw, 10 to 11. Soldered 1M between pin 2 and 14, cut trace between 1 and 2, then .47uF SM cap from 2 to diode to pin 6 to conduct when pin 6 is low. Latching failures seem quite common with DD2 and DD3 according to the archives. The line to the led had been squashed against the power-in socket. The input socket switch only functions with battery power Roland BOSS DD6 effects pedal ,2002,(no repair but did create a noise generator , see tips files) Dropped into warp mode of its own accord then failed to move out of bypass to any mode Originally thought the mode switch/pot was flakey because about 12K left at the end of the track, not knowing internal endstop, so beware. Thinking bad contact could make the mode selected be "0" , the warp setting. Mode selector switch on a Boss DD6 effects delay peadal. Looks just like the other 3 green case subminiature pots each marked B50K , by Alpha. Nothing external to indicate the 7 posistion "switch" is different. Inside a second properly molded-in internal endstop as well as the normal one, so track is limited to 3/5 of normal full track. So if wiper breaks, due to grease, then pedal has a mind of its own which mode it wants to be in. When cleaned out measures 0, 3k, 8.1k, 13.4,19k, 25k,30.6K in the 7 positions and over full track 48.6K. Pot used as a mode switch yes, with vague areas around the knob designating the mode but not ever seen a dedented pot before. And how are they assembled at manufacture.? Externally there is absolutely no different appearance between the "switch" ones and the pots, I've looked under an inspection lamp, no odd dot in the molding or any other difference. If you turn the shaft then it clicks into the dedents, being the only difference, but that is not visual. functioning as a switch, relying on high linearity and non-variation of resistance for firmware interpretation. There is a difference to the pots, they are ink stamp marked 2G on the side, this "switch" one is marked 2H7 http://home.graffiti.net/diverse:graffiti.net/pot_sw.jpg Laid out on a clothes peg and mm rule. Third part is the track section inverted to show the second green endstop. The fourth image unclear in pic, as buried in the body, holds the dedent wiper. One detent that shows is to the right of the purple > and the endstop arm marked A testing the 9V line , ohmic, varying 150 to 250 ohm and drawing well over 55mA spec current. unidentified ps components Perhaps voltage regulator or bucky controllers BJSQ 5 pin , size of body area, 2.8 x 1.5mm, SOT235, IC9, Overheating ps components same physical type but top code JAPL 4 pin on perhaps a pass transistor, size of body 4.3x 2.4mm, IC6 JB1G (number one not I) and printed as 2 pairs , Q15 Replaced with sm BCW67CTA , to proceed. BJSQ replaced with a LM317 set for 3.6V as the datasheet for the AK4352 DAC said maximum ps was 4.6V but was driven up to 5V via Q15 and DAC and ADC seemed to run ok at tehat and probably suppoosed to. So don't know what BJSQ was , perhaps a supervisory IC. Back to some useability but still somewhat high consump[tion. Testing 9V line now , probably as it should be, Diode check 1.1V / 0.6V and on R like testing an elecrolytic. Test connector pins 1 gnd, 2 pin 19 of IC5, 3?,4?, 5 IC7 pin1, 6 2100 supply, 7 ? ucontroller responds to function changes correctly but audio output stays at bypass. That u sends data that varies on function change to pin 63 of a Boss proprietary 100 pin. AK5353VT ADC sends data to pin 68. There is data flow to the RAM but otherwise nothing comes out. The AK4352VT DAC is ready to receive but nothing there. This main Boss chip runs warmer than should and more than the 55mA consumption , in specs In this non-working state and deliberately feeding with 7.4V and not 9V, the 5218A supplies are 6.6V and the 2100 like the main chippery is 4.3V, probably should be topped out at 5V , regulated with full 9V Boss ODB-3 bass overdrive Sometimes fails to work or stops on battery and sometimes on adaptor. The plating on the power socket metal parts was breaking up , presumably interfering with the switch contact as well. Bullet VM30 combo, GDR from 1990 But looks more 1970s . Pull+slide the covers off the handle to release and springline ICs marked "X2 080" ,"X8 761" ,"TL 761" (not opto) ,"X8 082" ,"X6 081" ,"X6 082" , V4007D B080D = TL080 B081D = TL081 B082D = TL082 B761D = TAA761 V4007D = CD4007UBE the X* numbers are datecodes 2x KD607 80V, 10A, SD339 and complement SD34? SD335 , 336 on preamp , 2x330R , 120R An E-line size or varicap type package of a diode like SAY32 marked 32 VV or 32 YV, 32 volt zener ? The ones marked 15 are the zeners for setting the +/- preamp rails. Works for 1 second and then fades out. There was a burnt section of the ground track between the secondary ps side of the preamp and the signal side. The grounds of the 1/4 inch sockets were measuring 6V. Bridged temporary with 68 ohm and measured .6V so bridged with a fuse holder and 1.6 amp Probably due to operator "error" and have replaced with a fuse there. The siting of the ones marked 32 maybe for overvoltage sensing , but not normally in service. Probably those are 32V zener. There are 2 more of that package on the preamp. These labelled 15 X4 and next to the +/- pass transistors for the preamp +/- rails so probably 15 Volt. Springline 315R and 10R, if the 10R one is disconnected there is distortion to the output with reverb set to zero. Repaired now, but for the archives there is a safety issue with these amps. The earth bond wire to the amp chassis is fine but the bond to the front panel metal is very poor, just a brass rivet to the phenolic of the pcb, of a few ohms drop over the years. Needs redoing to the metalwork properly. Carlsbro BassBeaver, 20Kg Broken pin on input socket, desoldered but soldered wire to the remnant and soldered to the nearest component down-trace. While in there noticed a burnt 2W resistor that was o/c. This was a snubber at the speaker output consisting of 1uF,100V non-polarised electrolytic and this resistor. Remaking the remnants of the R it was about 3.9 ohm. Nothing on TDA7293 product pdf. Replaced with a 2.5W, 8.2 ohm with long solder joints along traces. As probably o/c for months obviously not too critical The R-C combination is a Zobel network "can be quite important to the correct operation of the amp. It's purpose is to neutralise the inductance of the speaker voice coil, with the intention of flattening its impedance curve at the HF end. However, without this network in place and doing its job, I have known output stages to burst into spontaneous ultrasonic or even RF oscillation. The values of R and C are calculated according to some esoteric formula that I'm sure real audio buffs could quote at you chapter and verse, but the general rule of thumb is that you start with a resistor of equivalent value to the voice coil's nominal impedance, and then calculate C from there. " - Arfa Daily also http://sound.westhost.com/highspeed.htm#a33 +-41V, uses TL071, 072 Resistors 150 ohm, 2x680 and the unknown 2W Carlsbro Cobra , 1986, 28Kg Someone threw something at this speaker in a Carlsbro Cobra combo. It works with distortion, like a weakened form of one of a pair of complimentary drivers working only. By digital probing (using my fingers) at about 4 o'clock position , unpowered, the rubbing resistance feel to movement of the cone disappears. Same if powered up, no distortion, to a power level where the effect of my fingers damping comes into play. A liquid that will contract on drying to paint radial stripe on cone and dry and test, repeated until problem goes plus one or two more stripes.? Or would freeing the rim or part of the rim of the cone by hot-air heationg and reseating all or part be better. If part then release 2 to 6 o'clock say and pull or 8 to 12 o'clock and push, my guess is pull would be better. The central dome was buckled in so attacked this first. Drilling a few 1mm holes and using a dental sickle brobe managed to pull it back into reasonable shape. Somehow that corrected things, just a small puncture in the cone periphery to patch over now. Uses 2x 3055, 2x1C03, 1C04, 2x 10R, 2x 0.24 , 150 ohm on phones line in the pa. TL071 s , 2x680R , RC4136 on pre-amps +-44V dropped to +-15V Someone had been in there before and managed to disable the reverb. The transmit side of the springline wire has no earth return, just a dummy pad on the pcb. That person had soldered the braid of that wire connected to the receive ground to the driver output. Tracing the RC4136 quad the spring line driver output is pin 3 o/pA via 100 ohm to springline and 220p+100K return to "A" i/p and via 100 ohm to i/p(D). Receive side of springline connected to pin 9 i/p(C). Carlsbro Eclipse 12, 1998, 12 ch mixer amp Drummer laid his snare drum brushes by the side of the amp and the wires flicked into the vent slots on the side and killed the amp except for front panel lamps. Replaced 2SA1668 pre driver, and FS7 fuse and added "crockery scourer" grill cloth inside the vents either side. Also for personal H&S cut off all the jagged corners on the sheet metal work with double action snips. pa uses MJ15024 / MJ15025, 2x 2SC4382, 2x 2SA1668 , 2x 4580, TL071, BA10393 , 4093 IC03, 7815,7915 digital board TIP132, 7805, 7815 discoloured 220R ?, measured 265R over each in cct. Disassembly, remove side panels, remove top and then divider panel 5.7V, -15, 15, 15/5/50V, 47R in cct, 2x 10R PL4 for LCD display panel PA works with all mixer panel disconnected PL7 2,2,2,2,2,2,7,7V PL3 0,15,13,13,2.1,0 PL4 6.5,6.5,6.5,6.5,1V PL8 2.2,2.2,2.2,7.2,7.2,7.2,2.2,2.2 PL1 -12.8,2.5,17.5,26 HT 68,0 main bridge rect ac 102V, 138V dc othe rbridge 18.8V ac Carlsbro GRX7, 1996 Sometimes failed to work and sometimes dropped in power and crackles. All the 1/4 inch sockets needed attention, front and rear. The signal pa/preamp interconnect lead needed attention The subsidiary +rail 156R dropper needed replacing. Uses 4x MJ15024, 2x SM2177A, 2x SM2178A, CBC182A, BC212 1C03 , 2x TL071 156R, 5x R33, 10R,2x 4R7 Mains primary 6.9 ohms uses +/-15V regulators on preamp Carlsbro Hornet 45 lead, 1984, 17Kg Distortion. Problems with output transistor, poor joint at base for some odd reason, heatsink hold-down bolts not tight enough. Soldering generally did not look very good - flux residue problem? - re-did all power handling ones. Uses BDW93C, BDW94C, RCA IC02, RCA 1436 Rs one measured in circuit as 156 and 2 not larger than 0.3ohm. Put a union in the speaker cable for ease of repair. 2 pairs of side screws at rear release the rear panel and front ones for front panel release, springgline fixed to centre board. Unusually the amp separates into 2 sections separately connected to the wooden casing and so electrically isolated as far as any earthing. The mains transformer is on the rear panel which has a proper earthing point from the IEC mains inlet. Power supply is plus and minus rails but the common is not connected to ground at all. The power and signal lead to/from the pre-amp / reverb is 4 lines : plus , minus , common , line level signal with no earth connection. The front panel is connected to the common , not to earth anywhere. There is much more noise immunity from general stray pick-up if I run a wire from the earthed back plate to the front so bridging common and ground but left as is. Interestingly this unit was yearly PAT tested and passing presumably earth bond and insulation test each time. If they had checked insulation resistance relative to the front panel , he assuming it was earthed, then could that have caused damage.? Carlsbro Marlin 6-150 m2 1987 Insurance write off -not working after being in a room with a serious fire not associated with this amp. Some minor radiant heat damage and smoke stained but failure probably generally relevant to other equipment in similar circumstances. Although there are no ventillation holes with these amps there was considerable smoke deposit on the inside of the amp. The concentration of smoke must have been so great it had penetrated through the 1/4 inch jack socket holes. All these sockets needed cleaning but the real reason for not working was smoke entering the mains switch and IEC integral fuse holder and insulating the electrical contacts. Power devices 2 off MJ802 ok . To gain access remove one case end face,slide out top and bottom pannels after marking and disconnecting springlines. Remove the rear heatsinks to get to the power TRs that unusually B and E fix into screw terminal blocks on the pcb. Carlsbro 8400 , 2003, 400W mixer amp that immolated itself. Remove the front panel first to work out which screws on the back to remove. Q319 is a high voltage TO92 ( totally burnt and erupted but 2 isolated lighter blobs on the remnant of TO92 face are in the position of the isolated printed 2N of other 2N5551s on the board) then the melted blob component goes from the base of this feedback transistor to the speaker output line via the relay and choke. But it was 2N5401, (from the obtained schematic) which did not have a match elesewhere. The board is also burnt so overlay for this blob also missing. Anyone ever come across a metal oxide resistor melted to a 3mm diameter blob like a small tantalum. Metallic grey blob that measures 40 to 150 ohm or so across diameters, was 1/3W reistor of 330 ohm. The thermal heatsink monitor tranny was also exploded but as the face was gooed to the heatsink, that face was spared from charring/shattering and that was 2N5551 also, the thermal switch is 105 deg C. The subframe inside the chipboard casing is held to the chipboard with 12 x 4mm bolts, into clinch nuts on the outside covered with the black vinyl. 2 had dropped out and because you carry this kit vertically but use horizontally, plenty of chances for 1 inch long steel screws to roll into the power amp. But only plain washers and not star or spring washers under the heads and no varnish /glue spots over the heads to stop any undoing. On reassembly all internal bolts were replaced with star washers and glue spots. Audience were treated to piles of smoke erupting from the back of the amp - Hendrix was more impressive. Plenty of other damage but identifiable components for the others. 3 .5R, as well as above items and even a 5mm wide , current reinforced with solder, track had burnt. Copper trace 3.5 x .02mm and as 2 half approximated elipses of solder then area of 1 elipse of tin+lead which is Pi x a x b , a and b minor and major axes of .15mm and .8mm. Copper fusing current of the trace = 12 amps Lead+Tin elipse then 6 amps (not as much as I would have intuitively thought) Total 18 amps so 18/4 = 4.5 amps conventional fuse rating. Presumably the circular to sheet allowance would up this 4.5 amp figure , but by how much ? What sort of correction factor for thin sheet/non-circular heating then rupture allowance? I had a play with track width calculator http://www.pcbco.com.au/tracecalc.html and assuming it is still sort of valid at very high temps. Putting the melting point of copper of 1080 deg C then for 3.5mm strip of presumably 1 oz copper then the rupture current would be about 48 amps which seems reasonable. I knew it must be higher than 12 amps as that calculation was for round wire. By 1080 deg C we can forget about the solder run beefings. I think, assuming they survive ordinary power-ups a few times, I'll settle on a mains side 4 amp anti-surge , with a 5 amp A/S ready to hand spare and 2 off 10 amp quick-blow in the DC lines. Emailed schematics from Carlsbro. Oriental script on the mains transformer and on a schematic. Q319 was 2N5401 and the R was 330 ohm. I'd not thought about it but VxV/R heating with single rail of amp voltages of 65V to melt a 1/3W resistor, not charr or explode it, it must be about 300 ohms or 10 watts dissipation. Uses 47V-0-47V ac, 3x 2SC5200, 3x 2SA1943 2SA1306, 2SC3298,2x TIP41C, TIP42C 2K, 6x .5,5W 2x 47 Replaced output trannies with lower voltage, higher current but much cheaper TIP35C and 36C and 2SA1668 to 2SA968 and 2SC4382 for 2SC4159 On bench tried powering with half rails of +/-30V , too low for relay to click over and no load at all. TOP66 of shorter form than the originals so ground split some standard spring to heatsink retainers and ground a small notch in the end to engage with the mounting screw plus star washer and glue dab and sprung against the tranny body (with glue dabs) so using existing mounting holes. With these lower rails .3, 30, -.14 and .8, 30, .3 on "positive side" TO220 and TOP66 .8,30,-.3 on thermal feedback TO92 and .13,-30,-.07 and -.4, -30, .13 on "negative side" Full rail voltages not measured. +/-15 V on the separate TO220s With amp outside cab but in normal vertical position and 7V ac of 400Hz driven into 4 ohms then temperature of thermometer clipped to the top of the big heatsink stabilised to 27 degrees over ambient in 35 minutes. No need to remove all knobs etc to acces the preamp control section of pcb. The master volume slider pot "knob" was broken , owner used a match. Plenty of sideways room to keel the slider over to glua an extension to the side. A bit of black cable tie bent and glued to double up in a vice. A bit of a bend in this piece to roughly match the leaning pot. Desolder the 2 pins on one side to lean over and introduce back into the cover and resolder after positioning better. Carlsbro Marlin 6 150 IV, 1995 ? ps +/-44V prea 2x 1K pa 2x 0.3R (in circuit) 2x 10R,150R TO3 nearest signal IP line probably NPN Beware the effects switch at the rear can give this "fault" as well if falsely engaged. All pots "worn" to the extent that its harcdly possible to find a position on any of them to pass a signal to the amplifier , so effectively dead when the main vol control becomes extremely "worn" as probability of blindly finding 2 active spots in a pair of controls with 90 percent defective is unlikely and pretty useless if found anyway. This occured at a period of cold weather which may be contributory. The pots were not worn as such. Believed to be the original lubricant had hardened over the active pot surfaces. Renovated all 8 gain pots and treated the bass & treble pots with meths bathing , both as per tips files. Tx 9.7R//0.4R,0.4R Carlsbro Marlin 6-300 Mk 2 1986 Blowing fuses. TR7 TIP41C s/c all round,R (R21 ?)between C10 and VR1 burned but probably 1K,R29 burnt replaced with 100R, other damaged Rs R9 22K ?, R13 3.9K ? R14 1K ?,22K ? preset burnt out. 3 of the 4 2N3773 defunct. As an interim replaced power devices with 4 x 2N3055 while checking out biasing section before replacing with 2N3773s. This amp had been repaired at least once before so cannot be sure if correct components or voltages but from repaired amp :- Thermo feedback used a BC182B, unknown CBC640 small BC182 type body in 60V section of circuitry. Other devices RC4136N and TL072 . Driving 8 ohm load DC voltages reading from heat sink side on track side of board. 4 2N3773 0,61.5,.4;0,61.5,.4;-61.2,0,-60.9;-61.2,0,-60.9 then row of TIP41C,42C,42C,41C .4,61,.9,60.9;59.7,.9,60.2;0,-60.6,-.5;-60.6,-.4,-60.1 Carlsbro PM10 o/c powertone speaker , ITF, 6.4R replaced with Eminence Alpha 10 uses TL071 mains tx 21R, 1.8R Carlsbro PM15, 2001 Dual purpose 200W PA head or a foldback monitor. Reported occasional loud bangs and pops without any signal input, otherwise no distortion. Of course I powered up and with any amount of banging of cabinet no induced problem. Took apart ( need to remove the 15 inch speaker first ) and powered up with twizzle stick and serious bangs and whistles can be induced by tapping in area of electrolytics C1 (4.7uF,63V )and C3 (47uF,63V) and 2 small signal MPSA92 all at input from pre-amp. C1 probably AC coupling from pre-amp and C3 local DC rail decoupler. Otherwise no dodgy looking fuses, spade terminals hotspots or suspected dry joints anywhere. Replaced the caps and resoldered the trannies, removed Cs seemed ok and one trannie pin/solder did not sweat properly , contaminant ? TR3, SM2178A voltages, -59,-0.6,-59.8. 2 possible dry joints on this TR3 so added insulated heatsink tied to the pcb with cable ties. 45V ac on both fuses 60V,-60V on bridge rectifier uses TO3 devices BUZ906D & BUZ901D power to preamp 15.6V,-15.6V dc 3 sets of 8 screws, machine bolts on speaker, washered screws on front grill. Carlsbro PM65-100 , 1991 stage monitor amp-speaker , Carlsboro No repair as problem was in external feed. In exploration a 100R resistor next to TR7 was charred but functional,replaced with 1W. Replaced S M marked pnp TO220 trannies 1C04 with TIP41C and npn 1C03 with TIP42C. ( for 1C03 use RCA1C03 and RCA1C04 for 1C04 to find data ) Supply rails +-44V TR3,7,6 voltages -43.9,-.52,-44.6 -.52,-44.1,0.1 1,44,.5V Carlsbro PM65-100 , 1990 stage monitor amp-speaker Loud buzz plus hum and no power LED on front. Someone had been inside and fiddled because they had moved the header to front board one place out. So + feed not connected. Still a buzz when put in correct position or disconnected so presumably original problem was on main board. Erroded "dry joint" on -ve pin of the bridge rectifier so remade all pin joints. TR3 marked S M and 1C03 ? ICo3 ? 1C03 ? IC03 ? replaced with TIP42C as seemed to have been running hot for no heatsink. Carlsbro S600M, 1981 600W slave amp triac ? mains power protection, th/sw on heatsink plus other stuff monitored presumably. Its in an awkward area to get to, a lot crammed in a small box. Anyone happen to no basic data on Carlsro badged TO3 audio o/p devices ERD1159 All h/s screws needed tightening but all unplated. Distinctive feature all sockets on the back XLR ,4 i/p and 4 speaker o/p one set of 4 female and other male. I cannot, cold, see how this setup works I'll have to desolder one each of the pairs of the th/sw (4 in total) , one pair for each ch , seems one parallel pair for normal fan use (in series to mains fan) and one higher temp parallel pair for overall cutout via mains triac. As all seem to be s/c cold, perhaps one of an o/c-cold pair is shorted. Then there is a triac crowbar on each output that presumably activates the mains triac, 3 triacs in all, to confuse matters So 2 n/o 58C th/sw in parallel for fan operation and 2 100C n/c th/sw in series for cut out. Can power up now having sorted that conundrum out. Power side works including the over temp th/sw system, now to somehow reconnect the signal lines. Unfortunately another problem became apparent. To avoid a 1 turn secondary on the torroid they passed the coach bolt through a second anchoring plate with some insulation. Looks like 2 cut down black plastic 1/4 inch socket outer rings. One either side of the hole in the plate, but of course not high temp plastic and have softened enough to deform , not actually making metal/metal contact but obviously not safe. Cut some PTFE discs to go inside the large hole and 2 pairs of sheets of PTFE either side to bolt down 7.6mm and 12.1mm diameters 100R via mains sw , due to triac cct primary 1.6R, sec blu/y .3R 2x 47R ww SM2177A +1 inside heatsink section SM2178A + 1 inside 4558 each ch TIC2360 as speaker protectors 2x 1500uF, 63V remove 4 screws outside air filter grill to demount whole power block 11v DC R/Bk at bridge R, for 228V on variac, later emerged this high V was due to triac problem I confirmed that the over-temperature sensing cct worked and the triac cut the supply to the mains transformer. I was running on a variac and with about 90 percent mains and with no load etc there was 0.1 amp current drawn from the mains and a noticeable amount of transformer noise I took to be saturation noise and current drain, more than I'd like but until I could confirm with the owner about previous useage, I let be for then. This time I powered up and 1 amp being drawn with no load at only 70 percent mains. Disconnected the secondaries from the amp and still the same. Disconnected triac circuit and the transformer is happy to 100 percent mains, fed directly, and only few mA of current drawn. What can be going on ? To get to the triac componentry proper requires a major strip down first. Could it be half cycle firing and causing some sort of magnetic mutual/resonant/self-induction effect that is causing excessive current? A matter of isolation transformer and scoping some dropper in line with the primary to see ? No obvious heating on the triac, only a small heatsink. I was monitoring the DC last week and it was already a bit over the 63V rating of each electro. This time direct to mains, no triac, it was much more normal, forgot to note but about +/- 55V probably at 100 percent mains Scoped the secondaries and a cross-over distortion developes on increasing the variac voltage, not particularly strongly, but definetely there, and increases with voltage increase and "saturation" current/mechanical noise. Placing an isolation transformer on the primary with a 25R/20W dropper to "neutral" and scoping, then the problem was obvious ,now unfiltered by the transformer. Could now run up much higher variac voltage because of damping by the added R but even then there was 3mS duration spikes of peaks twice that of the mains ac pk-pk of mains (UK) 20mS period. So some sort of bucky inverter effect going on. What to look for around the triac when I get to it ?. To get to triac area, 8 XLR connectors with 3 stout wire standoff conductors each to cut, probably by grinding through the most enclosed ones (then desolder both cut ends and replace eventually ). Because audio input and output and mains control all on the same board with no obvious isolation band between the sections Carlsbro Viper bass combo, 1990 , 25Kg Pops and bangs then drops out after 20 minutes, starting ok again when cold. Vibration induced failed dropper joints at the preamp 15 zener supply rails. Redid droppers tied together with silicone rubber sleeving and silicone rubber support pads and replaced associated caps has one had probably leaked. Redid solder joints on major leads on pa as 2 would soon be a bit suspect. One 1/4 socket broken, the other weak , replaced with stouter types , upside down and cros-wired and located in place over the intrusive switch for one. Rails +/- 44V , with back plate horizontal and feeding with 400 Hz and o/p of 6W continuous, then thermometer in the heatsink back bracket stabilised at 75 degrees over 20 degree ambient after 40 minutes. Uses 2 x 3055, 2x RCA 1C03, RCA 1C04 2x .24 , 22x 10, 1K 1/3 W 4x 4558, 3x RC4136, vectrol linear optocoupler 2x 470 ohm Carvin Pro Bass 100, PB100 Blown o/p , maybe started with poor solder, hot spot, small burns at solder pads, device Carvin marked 60-72940 , replaced with TDA7294V 15 pin device to 10 wire ribbon H2 15V,0,-15,sig to pa H5 1 sig in, 2 gnd, 3 stdby, 4+5 + supply, 6+7 - ps, 8 mute, 9+10 o/p Carvin Pro Bass 100, PB100 Any movement of the frequency pot for mid band lift created full DC bangs. Ultra-miniature pots that have next to no metal for the wipers. I assumed gooey grease in the pot was sufficient to lift the wiper from the track which in itself had no wear. Decided to replace the pot with sub miniature pot but as overall length less, padded out with a block hot-melted to it and board and extended connections. Uses 4558s apparently dated 1983, although Carvin WWW schema for version B dated 1995. Used black 4 lead opto-coupler Vactec/Vactrol LED -ve at notch corner, cell at the other end. Used 15 pin hybrid 100W,100V labelled Carvin 60-72940, 2 large Rs, 820 ohm,7815, 7915 The rattle noise on moving the amp is a spare fuse in the IEC socket. The amp to speaker link needs the elbow jack replacing with conventional, just enough room. Poor mechanical connection at the elbow means a resistance and voltage drop, heating the plastic disc that is all that forces a mechanical connection so progressively worsens. Carvin X50B tube amp, 1989 Told the amp was not working Amp seems to work perfectly well, being repaired for minor problem , broken wire at the return of the external effects loop so not working if externally connected. no succeptibility to microphony or tinging distortion. Testing the 2x EL34, gains are good and matched but after a minute on heated C/H insulation check, the resistance gradually decreases to 1M for one and 0.5M for the other. What problems will this lead to if continued use, and how quickly ? The amount of leakage apparently is no big deal for power tubes, if it gets below 100K then have a hum problem. I was wondering if there could be some sort of thermal runaway situation. Measured no more than 1mV rms hum over 4 ohm output for this one , level set for 2.25 W of 400Hz output, but disconnected and monitoring for shorted input. All pa W/W measured in circuit at about 350 to 380 ohm. 470K, 2W 5 x 4558 , 4049 + 4x 4558 240V primary 4.3R Secondary red , in circuit, 32.5R yellow/yellow 1.2R blue / gn 2.2R large gn wires heater supply H2 wire colours Bl,P, D Brn, R, Lt Brn, O, Lt P, Lt Blu, Bk,Y,Pk H4 P,P/W,O,W,Y,Brn,Bk,Bk,R,Gn H3 voltages 0,-15,13,0,13,0,0,0,13,0 470K , 10K Someone had been in there previously , maybe removed R arounfd the Master pot. Could not see why they would employ just 1p 1w of 2p2w switch and no use of the pot. Placed a 680K R where R13 on the overlay . Load test , thermometer wired to a 85mm pickle jar lid , balanced over the 2 bottles 4 ohm load, 400 Hz giving 3v ac over 4 ohm 15 minutes to reach 40 deg c over ambient and 0.06V ac increase Casio CZ 5000 1985 keyboard No function,LEDs or LCD display The only convenient 0V point for the TTL I could find was the -ve pin of the ps bridge rectifier. No 5V for the TTL. It looks as though the keyboard had been dropped as the large electrolytic on the ps had moved and consequently the track continuity to the 5V regulator part of the ps was broken under the capacitor pin,not obvious at al. With all 3 connectors unplugged and PA order on main pcb not the ps end which is different order. PA 0,15.3,-16,0,5.6,0,5.2,0,5.2 PC 0,0.03,5.2 PD 0,16,15.3,0,0 Casio WK 3000, 6 octave keyboard,2003 Intermittant loss of left speaker. Attended to all ps/pa solder points and conneections and desoldered headphone socket and remade. Open case upside down , from the rear first and then free the keys section. Work on it upside down with the keyboard section innermost. 3 pin TO126, device marked S2003 marked D for diode on overlay , only 2 of the 3 pins connected and diode and resistance test to the other 2 pins probably o/c so n/c ? All else functioning perfectly, but seemed odd using 2 of 3 pins. A nice stable 5V over the 2 pins in the ps area, so that a 5V, 10W (with heatsink) zener diode was my assessment. No heatsink used on this one but a useful TO126 format for say 10W zeners that are bolt-downable. Uses LA4636, 2x 2068,Sharp PQ1CG21H 3,1.2,0,5,14.8V NEC upD63200 dual DAC , pin 15 serial data in Al caps 2.2V, 2.7,5, 3.3V , SM tand 0.8V 2x wired caps on uPD65881GK062 gate array on underide of large board 4.9V Ami LP62S2048-70LLT 256x 8 SRAM ps to main processor board ribbon , starting red 5,0,5,.2,,01,2.9,0,5,14.7,5,1.6 (o/p signal line 1),1.6 (o/p signal line 2),0,0,2.7 D shaped recesses in case for washered screws On first powering up it plays dumb, display echos the key presses and midi functions normally but no sound out of the built in speakers unless you wake it up going into demo mode for a bit. Nothing wrong with mute/standby functions of the main amp and low level hiss from the speakers so not headphone bypass problem. Possibly on powering down "local off" setting for midi use is stored in the memory. Seems no access via the keybpoard/keypad/buttons etc to alter this, must be via an external pc/midi link. But just pressing "piano setting" resets a number of things , one of which is setting local to ON (if OFF), in the troubleshooting guide , if you have a silent keyboard. This Keyboard not used via MIDI But there must be some powerdown (or power up ) fault creating this random occurance (left unpowered overnight and powered up perfectly ok, despite deliberately switching off at the mains rather than powering down via the power on/off button). No obvious on-board battery , although overlay symbol and unpopulted section of the main board has this for some other model type. The corrupted memory is on 'song memory', keyboard ges silent after the owner pressses that button to recall previous recordings. Probably corrupted when writing to it when someone pulled the DC supply plug out of the back. Citronic SSL 1001 Sound-to-light unit No lamp function on any channel Fracture of a pin on 4025 due to corrosion at juncture of legs and solder.Other ICs looked similar so removed all and replaced with socketed new CMOS ICs.Note for personal safety when working on the logic circuitry disconnect from the mains and power the logic between Vss and Vdd from a 10V bench power supply. Crate BV150H, 2003 ? Blown fuse blackened barrel, replaced and then intrusive hum developed After testing all valves and on removing could see a dark opaque patch on the inside of the glass envelope. Broke in by sawing off the bakelite locating spigot and using a hole punch on the evacuating pip and found a bare metal patch on the anode/plate , otherwise grey coating. Breaking into that there was a patch of missing white coating on the cathode opposite this patch. Connection between cathode and G3 is fused / broken link , presumably very high current passage cathode to anode, what could cause it and how much current could pass ? Before I broke in the getter was usual metalic black appearance The getter in the cap is now white caesium oxide or whatever (in a sealed bag i might add), the black patch is still matt black. A square patch on the envelope, square because that was the boundary although not extending to the glass, looking like a spray paint squirt but square rather than round I would say the patch on the anode looks as though it has thinned but not punched through, so perhaps the metal plus whatever the grey coating is condensed onto the envelope. No trace of white in the getter on the cap until a few minutes after I broke the evacuation pip in the base The opaque patch was constrained only in the section of glass containing the section of anode with the burnt patch. Neither mica spacers or plate metal fully close the gap to the glass so any of this material could have gone through those gaps but didn't. This sugests to me some sort of directed jetting action. Normal more metalic looking getter cap coating at the top of the valve was still present before I broke in. All 6 6L6 were of the same batch and none of the other 5 had this side opaque patch I cut the pins at the base of the envelope to see into that area under the cathode column and the ribbon that connects to the cathode tube is spark eroded ? to a break. This ribbon is 0.5 x 0.04mm in section, if it was copper then the rupture current would be about 6 amps Mains transformer g/g 0.1R, r/r 7.1R, or/or 0.9R, bu/bu 1.8R o/p tx 11.4R/13.9R pa 6x 1K, 2x 30R, .1R, 2x 150K, 220K, 4K7 preamp 6x 10K, 1R Mains transformer wire colour coding probably like Blue Voodo 60 (BV60) but this one 4.5x4x5.5 inches, audio o/p 4.5x4x4 and no choke With 7 mains primary wires set as Bl+w/w/bn/V and 199V as mains then 5.65 V on all 8 +6 heaters and 407V HT1 and well over 6V ac on 240V. According to owner , bought it off company rep a few years ago and is export version prototype. Blew a fuse a few weeks back , runs still ,after fuse change (self heeled cap?) but excessive hum. 450V rating ps electros but I measure 488V on the HT rail and varying ac (4 to 5 volt ac measured via 1uF, 1500V polyprop), perhaps seriesed-up, but 3 in there, I've not taken apart yet. The neon lit mains switch looks more like a light bulb , runs too hot to keep your finger on, I suspect droppers for USA mains inside. No serial number on the chassis No mains voltage stated at the IEC inlet, just fuses for 110 or 240V, 7 wires to the primary side of the tranformer and jumper spade matrix inside. As the rep was going around Europe , not just the UK . Powered up and looked for voltages off from 0,110 or 240 . No smoothing choke for this amp it would seem, unless its in with the mains transformer . As the mains switch is made for 110V use then anything is possible I should have said previously only the 110V and 230V fuse ratings stated on the chassis, not 2 separate fuseholders, so someone might erroneously think it was an "intelligent" ps , no external selector switch or helpful labelling of selector matrix inside, I'll explore that later today. All valves test ok except one 6L6 which, apart from heater, is totally dead, no gain at all at any anode current. There is opaque stain on the envelope in area above pins 4 and 5, localised in that area, although it could pass beyond the non-round, mica spacers. I assume some metal melted and evaporated/jetted onto the glass like the getter process. I assume this could have been plasma arc to anode and excessive current and blown mains fuse, as that part of the amp history. What would have happened here ? I will break into the base/glass pip/cut-ring the envelope and remove the innards to have a good look as presently cannot see anything through the deposit. A melted hole in the anode? what would physically stop any valve action? the getter is still silvery. Not yet retubed (that one plus another removed for balance) and tried out on reduced mains yet. Other than heater continuity it tests as though no valve placed in the socket. Same colour code of primary, not secondaries , as that blue voodo and seemingly the same significances. But I'll have to take apart to check what is jumpered to what, and also the HT1 smoothing is different as it uses 3 , not 4 caps there. I forgot to check each voltage on the 7 primary wires, will do so next. With the duff 6L6 and one other removed Putting 199V on the existing setting of primaries gives 5.65V ac so suggesting 6.53V ac if 230V fed in on existing internal set primaries. Is 6V ac on that Crate BV60 schematic a strict ie +/- 0.1V, or nominal 6V (with all 14 heaters supplied presumably) Also 199v "mains" gives 407V HT1 The hum is present but with my variac I can lift the ground and doing that, the hum goes and amp works fine , normally testing an amp there is no hum and lifting the ground can introduce hum , so I wonder what other problem lurks. 1000V megga test on the mains Tx shows nothing amiss to ground. Looks like the same colours but not necessarily the same taps. Monitored the total primary resistance and marked, removed/replaced spade connections until 3 spade connectors blue , grey and black removed without affecting reading . Leaving blue+white stripe, white,brown and violet as the primary. Powering up on 199V wrt to neutral the free wires read blue 190.3 grey 86.4 black 206 wrt live blue 8.3 grey 120 black 8.8V is this the setting for 210V, 230V or 240V ?, I'm trying to get the maximum number of turns as the primary. I'm thinking I need to swap the blue+white with the black lead. If complete agreement with that Blue Voodoo 60 then the existing wiring is undefined on that chart, the J numbering does not tally with this one Broke into the 6L6 , I thought the caesium getter went white immediately but takes a few minutes, envelope safely sealed separately now. The outer grey metalwork anode had a bright metal spot adjascent to where the black envelope staining was. Cutting half the anode away revealed a bare metal patch on the otherwise white coating of the cathode, no pools of metal or smoke trails, G1 winding looked fine. I'm surprised how tough the mica/composite ? spacers are compared to similar I've seen inside toasters Exploring the 6L6 a bit more there was continuity between the base pin and G3 but the internal contact to the cathode was missing. Presumably a deliberate weak fusible link in whatever occassions a plasma arc strikes between cathode and anode. Looks as though the hum was associated with the input socket. This is designed to be isolated from chassis taking ground from screened lead. As it was turning round with tight bush nut I assume someone had been in there and changed the insulating bushes about so ground-looped, now isolated and tight and no undue hum. Looked under the pa board and it is 2 seriesed 47uF,450V for HT1 and the other one with a dropper for another HT. date 2003 or later. Mains primary now set for presumably 250V as heater readings are still a bit high. So with full mains on there and all 8 12AX7 and only 4 of the 6 off 6L6 reads quiescent 6.6V ac and 470V HT1 from 356V ac, other secondaries or/or 32.8V ac and bu/bu 66V ac. Incidently not only the neon /sw needed attention but the handle is crap and jagged sharp metal exposed inside, covered with nylon spiral wrap, then expanding nylon sleeving and then 2 layers heatshrink all under the covering now I cut the pins at the base of the 6L6 envelope to see that area and the ribbon that connects to the cathode tube is spark eroded to a ragged break. This ribbon is 0.5 x 0.04mm in section, if it was copper then I make the rupture current would be about 6 amps. Presumably failed at a weld spot so less than that Changed to black /w/bn/v probably 250V setting and 3 other leads left taped over and tied off the board. And perhaps bk/wh/bn/Vi 240V and bl+w/w/g/v 230V Blue wire interconnect "ribbon" pa-prea 395,0,0,17,0,-17,0,0,10,26 and white -6,7V 2x 4700uF,25V under pa board As not 2 replacement 6L6 at hand, temp added 3.3R over the heater supply to check and this gave 5.8V ac Crate GFX 65, 1999 Triple footswitch , no name , no ratings on switches. Impossible to use as a mind of its own which channel it wanted to be in. On resistance anywhere between 200 ohm and 100K on each of them. At least easy enough to get inside them, dissolve away the grease and deburr the rough edges and put back together again. uses .2, 3x .47 plus 4 1.5K, 3.3K,220, 2x10 5x 072 TIP42, TIP47 7x J175, 3x J112 primary 11.5R , secondary .5R, 60V ac Crate GFX 65, 2000 Green LED but no sound on Clean channel Someone had been inside with a power drill or something doing some "repair" and stripped up tracks and board. In particular the trace that goes past near the input socket that they were trying to "repair" With clean ch controls at 1/2 and 14mV, 400Hz, at input and DSP board diconnected IC1 pin 1 56mV , pin 7 360mV IC3 , pin 7 40mV TIP42/147 , 2x 047 ?, JE340 2x 270, 470, 0.2R 220, 1.5K, 3.3K, 10R 1/2W Remove 4 heatsink screws and 2 pcb screws and DSP board to release the preamp board IC3 pins 6 and 7 to clean level pot and IC1, pin 1 the trace to th eclean channel For testing needs a ground connection to both the PDCb ground points, PS and signal or nasty noises. Crate GLX65 combo of 2004 Uses miniature pots with clear plastic shaft and illuminator bulb inside the pot. Body 10x10x5 mm and even then space inside for a wire-ended bulb. The spindle made of clear plastic to conduct the light into a knob with red plastic inserts. Anyone know of an independent source of these. For future reference, as in for mechanically broken switch, all the pots are fine. Only 4 years of normal use and yet again flimsey push/push switches are falling apart. Replaced those with robust conventional toggle switches, enough room after bending the pins, wired across to the pcb, and only SPST use although they are DPDT switches. The mute switch is of stronger style. The compact LEDs illuminate the surrounds and the pot bulbs illuminate th epips in the knobs. 3 screws at rear release the prea section from the rest. Mark ribbons for orientation etc, to relese ribbons push the clusure strip. Reconnect cables before rejoining metalwork, double check you don't have 2 wires entering one socket, very easy with these lack of terminations. DSP footswitch mono, solo/clean/rythym stereo 1/4 inch Tx 55R// .9R,.9R pa 0.2R, 2x 270, 2 x 0.47, 220 2W, 1.5K 3.3K 1W TIP142 TIP147, 072,JE340 prea , foam cylinders go around stemmed LEDs Tx 55// 1R , .9 , .9 lights 40.5V at switch grey ribbon 3,2,2.5,3, .9,40,0 rhythm + dsp -41,0,11,.8 Crumar Roadrunner 2, 1979 , Italy, synthesiser Chorus effect not functioning. One of the 5 CA 3094AE not functioning but low level of output. Connected 6.8K between the chorus maximum level signal at one of the CA3094 and other end to the board output. The F 4727 was probably Fairchild 7 stage CMOS counter. ITT SAA1004 f divider. Mostek MK50240N probably = Thompson MK50240 top octave generator. If one key sounds but repeat depression does not then due to mis-alignment of contact spring. Un played the spring must touch the long contact rod common to all the keys to discharge or it will not play when depressed. Crumar Roadracer, RRC, 1978 One note per octave absent. AY-1-5050 Its a frequency divider , 7 stages , broken into a few isolated stages but in this use they are chained together so 1 4024 would do and perhaps 1 + 1/6 4049 for buffering. The trouble is the original uses 2 supplies -15V for outputs buffer supply and -27V for the logic. Buffered trannie input and running the CMOS 'upside down' between 0 and -15V ? Found an exact replacement so didn't bother fudging pinout in D.A.T.A 1982 digital along with AY-1-1320 and AY-1-0212T, MM5891 adjusted pinning may be useable there. Two keys were sticky. Not due to rusty pivot but under each key is a standoff carying a shaped rubber piece to stop keys swaying. Presumably going sticky , replaced each with a piece of 0.19 inch silicone sleeving minus cores. Perhaps squirting talcum powder under each key as maintainence may help. Gain access to underside of key by opening out the metal channel at the rear to release one pair of nibs on the white pivot plastic which allows to slide off the remaining 2 nibs. Slide the key to release from the hidden constraints but still stay captive by the thin and vulnerable switch contact. A nail wire staple hammered into the casing to keep the top switch plate away from the leftmost key. Custom Sound 2005, Mosfet amp, made 1988 Volume faded down after about 1/2 hour . No tranny/diode thermal monitoring of the heatsink and no FET for gain control in the pa or FET in the preamp , all 4558 opamps. No obvious over-heating or solder problems on any of the boards or flaky gain pots. Springline reverb throughput had failed due to corrosion on one of the springline phono connectors. This Accutronics springline was 200 ohm for in and out pickups. Dummy loaded (4 ohm and 6V ac) took the heatsink up to 70 degrees C and held that power level for 40 minutes with little variation in preamp output, pa o/p or DC rails so a matter of the usual treatments for the numerous IDC interconnects, sprung IC sockets and 1/4 inputs, despite no response to twizzle stick and reported fade. Dealt with all interconnects (stagger-marginally-bent the pins and cleaned to give better holding), IC /IC sockets and beefed up all 1/4 socket connections as 5 channel all in a row, by running silicone rubber cord the length over the sockets with Hama/Perler/Pearler beads 2 over each contact, fed onto pired up cord as in threading a sewing needle. Pairs of holes drilled through the pcb to take wire loops and a Hama on each to tension down the cord between each socket. Then hot-melt at the ends the down-pulls and the twisted ends of the wired tensioners. The mains fuse cap was exposed to a screwdriver so replaced. 2x 2SJ50 and 2x 2SK135 bf470, 2x BF469,2x BF423, 1K, 2x 1K, 7x 4558 on preamp Custom Sound Colt 10 combo amp Intermitent o/p like a bad i/p socket. Dry joint on resistor at i/p. Another dozen or so leads had holes on one side of the solder joint. It looked as though the lead cutter plate after assembly was blunt and pushed all leads over before cutting and it had taken 10 years for this stressing to open up as dry joints. David Eden "The Metro" Bass Amp,600W , 2000, 50 Kg Cut out in use then came back. Next time of use, failed to give output but owner noticed clip light in pre-amp functioned as normal Now I have it, I cannot induce it to fail. Likely suspects the discrete wire IDC connectors for power and signal interconnects, unsupported wire-wounds on end, mains thermal switch. I did not like the front panel switch in line with the speaker line. In standby instead of cutting/shorting the main amp input you switch out the speaker. IDC interconnects on the speaker lines and power lines seem a bit irregular to me but as cut out rather than distortion those power lines presumably ok. Speaker units check out ok. The function of the 12V, 10 W "festoon " bulb in the variable crossover in the cab is a fuse. Speaker switch rated 3amp and thats for AC, could easily be the problem, let alone potentially "fatal" to the amp. The cab wiring and pair of 4 ohm speakers in series seem fine. It would not take much fumbling in poor light, drunkeness, confussion or whatever to flip that switch in full use , its not recessed and in the back of the cab. The other 2 paralleled outlets are not switched, but I may hardwire/solder back to the pa. Found another nasty under the ps board but don't think it is the main problem. This pair of wires to the speaker switch had one of the wires squashed between a large W/W ceramic cased dropper under the ps and the chassis. Cut some high temperature silicone cable sheathing into a spiral, wrapped around the replacement wires and put cable ties to each end to. Original wires melted through but as it cuts the earth to the speaker, presumably no problem as such and wire not broken, just failure to sometimes switch out the speaker. But there is smoke blackening or something grimy in that area but it could be a small electrolytic parallel to the fan cooked as it is directly over the large droppers and leaked electrolyte but all rather nasty. The aluminium of the chassis directly under this particular dropper has a strange flecked grey corrosion or something that probably more likely due to electrolyte rather than vapours off the charred PVC insulation. The corrosion i've photoed here http://www.diversed.fsnet.co.uk/ali2.jpg The overexposed T area is the mains transformer and the groove marked "<" was created by the squashed/trapped cable or exposed wire core probably vibrating. From "<" to T only about 10mm so just 5 mm or so free gap to run these 2 speaker wires between mains torroid and high temp wire-wound dropper with no added high temperature sleeving. The grey flecking is what I'm assuming is electrolyte corrosion effect rather than burnt PVC product. If this fan lytic over the fan supply dropper leaked to short in use then dropper would generate more heat as well so compounding as well as shorting out the fan to the main amp heatsink. The owner had used the speaker switch in the past, during sound checks. The protection circuit is activating before the 60 degree centigrade fan switch is cutting in, under high load. The fan switch temperature , testing in isolation , is about right. The big triac on the mains, crowbar operation to blow the mains fuse if too much mains power drawn presumably, 60K to neon for UK and about 22 ohm in line between triac and switch. I've photoed the tracks and components and determined the schematic of this power amp. Hard-wired the 2 lines from amp to speaker outlet , there were 12 chances of a break in that route, to and return. 3 pairs of IDC and pin connections in each line. Using dummy load the thermal protection circuit was activating before the fan thermal switch. Monitoring the line from pa to ps with the LED thats on if all is well. The voltage changes as heat builds up from about -13.5V down to about 12.7V when it switches to about -0.3V , LED goes out and pa is killed. It was the LED on the ps that was failing. This LED passes current to the start-up hold-off circuit as well as turning off PA if the fan voltage fails genuinly or falsely. This LED also on over the high power droppers, replaced this LED off the board as well. If I'd thoutght about it I would have added a second board off the ps , bolted to the chassis with these 2 offending high power droppers on it away from the ps board. Bad design slinging them under the ps with active components over (heat rises). Added a 40 degree C switch in parallel to the existing Asahi US-602S , 60 C one but resets at about 25 degrees C. If one switch fails there is still the other. Replaced the MPS8599 with a BC212 rotated 180 degrees to pin match , in case the original was suspoect due to excessive heating if the fan had been stopped. Before pushing into the heatsink, check temperature controlled function of reducing gain to zero by a metal funnel leakily connected to a low setting of hot air gun and piece of heatshrink tubing on the small end of funnel. ps main voltages +/-78V dc. fan supply w/w dropper 75 R , 100R for preamp pa uses 10K, 2.7K, 3.9K, 4.7, .39, 150R 2SC3858, 2SA1643, 2SA1494, 2SC4327, MPSA43, MPSA92, J112A, MPS8599 Heat output measurements on 400Hz continuous sine i/p. Into 4 ohm load with room temp 19 degrees C, for 25W o/p in load, fan outlet temp 25 degree C for 52W , 30 degree C at fan outlet Dunlop Cry Baby GCB 95 Owner lost the original broken switch and of course did not note the wiring. Deduced wiring on DPDT switch Blue / Blue wire to pot Purple / Green (commons) o link o Needs a long stem footswitch eg Alpha L , 8D1 is too short. Never mount oe of these footswitches without the rear backnut as any force bearing on the flat body of the switch will break the weak brass nibs between the two parts. If too short , glue a 3/4 inch diam, 1/4 inch thick tap washer to the original felt pad and take up on the back nut. Dunlop Cry Baby GCB 95 ,wah wah,2005 From a wah-wah pedal only 2 years old so I don't see the point of replacing with more of the same, as these symptoms are very common. Poor bypass function and now total failure to switch between on and off Both 1.8mm x (11 down to 10mm swaged )stainless steel rivets ground off to separate the halves,push-push latching switch http://home.graffiti.net/diverse:graffiti.net/ppsw.jpg Unless anyone knows differently then I suspect the poor bypass contact is due to the interior packed with non-conductive grease. Carling, Mexico is the make of this one , single pole c/o, silver plated contacts and dumb-bell that can just about be seen in the centre of the top image,then a locating cup, then compression spring, then brass cup that seats the end of the swinging arm marked L in the next images. The dumbbell jumps the 2 contacts at the top of the image and runs along the continuous lower one, enlarged in 4th image, 5th is the swing arm magnified. some background on Carling switches http://www.tonefrenzy.com/articles/Boost_Pedal.html Featured Article :: A comparison of boost pedals :: by Ken Nossardi I think I agree with the comment in the quote about machine tool wear. I've not removed the rivet that holds the ratchet mechanism - maybe shown on a patent site somewhere. I suspect that ratchet mechanism, produced by worn dies, is just enough to bring that swing lever over to just over half-way when tested off the production line. With, now, no reserve for in-use wear. Cleaned the silicone grease out as not used for mains switching here, otherwise 1A 250V / 3A 125V rating. Why silver plating and then non-conductive grease in low current/ low voltage use ? There must be a "ball point pen" type latch action in the bush part so the down action pushes the L arm one way then the other on the next down stroke, with a click of its action on each upstroke. plenty of spring in the ompression spring between dumbell and brass cup, so no lack of contact closure pressure , leading to the bypass problem Presumably due to wear the underside of the button eventually bottoms against the end of the threaded part marked V, when L is only half way across. It needs to go a bit further than half for L to swing across, via the dumbell/cup spring sub-component action , to the other side. Slightly tightened a small Jubilee clip around the threaded bush, as a guide, and hacksawed off about 2mm at the V position, not apparent in these images, so can be quite neat. Stuffed more plain silicone grease in the ratchet section No matter, in this case (not mains use), may replace the rivets with Spanish windlass "E string" wire over 2 small soldertag rings and locked in place. Anyone know of a source of such small diameter /long rivets for other occassions? Of course just fixing the lack of switching does not require removing the rivets. In the end just used 2 small eyelets in the metal to locate under the back nut , 2 cable ties around and one across to remake. If there is non-conductive grease in other , otherwise 240V rated switches, then that could be a generic problem with all switch makes, used for low V, low A purposes. Dynacord Powermate 600 mixer amp , 2006 Supposed to have only a minor problem for repair but there is obviously (also) a totally black shapeless lump , presumably remnants of a burnt out capacitor. Marked C17 between F1 and F2 low power rail AC fuses. Anyone know its value? probably about 1nF, too low a voltage rating? or because it lies over a power rail track between D17 and C7, coating burnt off. Loads of these mustard yellow globular Cs around the board The output relays seem to present a short to the speakers in powered off mode, have not got to the solder side of the board yet to explore. RoHS construction, of course may present other nasties when I get there, not originally forseen. The muting TO92 J111 FET is falsely pulling down the signal line, -18V control V on gate dropper of both channels but not so the gates. Not the FET but the gate to ground cap going ohmic, see more relevant tips item on on WEEE/RoHS/PbF Mono operation secretly selected rather than stereo/2 channel operation. ? Both channel signals get to the mixer output jacks and the mixer ribbon is remade with both channel lines intact but there is a break in one throughput before the ribbon, but punch-in 1/4 socket bypass contacts are ok. I was being mislead by L & R on the overlay near the mixer/PA umbilical ribbon CN1. L is the L ch and R is the quasi ground for the L ch, the R ch comes in nowhere near it. Full signal L and R gets to the PA but only very low level gets to the R ch PA pre-driver stage, in for some messy opampish fault finding or false mute, if the power rails are ok. I've not seem them before, no name on the exposed parts of the connector. 0.1 inch pitch ribbon maker ?. http://home.graffiti.net/diverse:graffiti.net/idc_header.jpg views of connectors , same, both ends of the ribbon for photoing convenience. top as found, pcb part, ribbon part internals Black end pieces are just locators and for polarising,different sizes/recesses, not gripping the white bits. Locking is done internally somehow. Anyone know the professional way of unmaking these connectors? you do not umake the second IDC connection, per pin, in the process of separating. I ended up using a knife blade and then jeweller's screwdriver to get purchase between pcb and white part that goes down to pcb level, lacquer damage can be seen in middle view. A dentists sickle probe as a lever into the small holes along the white part edge levers it off. 4x MJ15004G, 4x MJ15003G 4x 4r7, 4x .22R, MJ15031G, C4793, MJ15030G MJE350G,MJE340G, BD241B, 2x LM317J, LM340T5 1K CN18, to CN8 ,55R CNS1 has +/- 15V, 24,51 F1 , F2, 40V ac +/-69V dc rails L bias signal ok fan blows outwards Rch mute, J111 Q303 preceeding opamp OP301A pin 1 L ch, J11, Q103, opamp 101B, pin 7 LM317 +16, -25 The J111 , falsely mute reads -18V, -1.1V and proper operation -18V, -17.6V 0.1uF/100V MLCC gone ohmic. Putting a DVM/ohms over this showed wavering 20K to 30K , same when removed. .125V 400Hz, 40dB gain, 0db slider ch1, 0db on master 0db on bar meter, 0.8V on l/r trace at CN1 main board 1/4 in jack in Main Output , L 0 ohm to L at CN1 Ribbon (L) 9 to mixer out 10(R) CN(4) sig (L) H1 SIL pin 4 CN(9) Sig (R) pin 2 of SIL H3 Dynamix Stage 250?, 1984 mixer amp Intermittant loss of one "tape" input channel Retaining bolts hidden under the feet. There are switches at the phono inputs and replaced them with unswitched ones. Uses 10R 10p16 , 10N16 4560D, 7915, 7815 springline 75R, 40R +/- 64V Electro Voice M/C 150 microphone Dead mike.Broken wire at the switch.To access unscrew the dome,desolder the wires to the active part. Remove XLR housing and then the 2 screws holding the switch to the body. Came bouncing back a few months later. It was now obvious the problem with these is the transverse pin bends. If the gust is held in place while the end of the pin is ground off and extracted and a replacement one made , then that would be the solution. Elka organ /AY1-5051 replacement From usenet discussion, placed here for clarity AY1-5051 Fixed Modulus Divider chip? It was made by General Instruments (later Arizona Microchip) and is a PMOS technology. a couple of salvaged 1978 , AY1 5050 in front of me with pinning, no knowledge if working order. With a DVM diode test and -ve to ground pin one measures .71 to Vgg and .66 to Vdd pin other is .8 and .74V for isolated dividers with no internal linking and a few readings referred to pin 1 as -ve to pin labelled input .88 and its o/p .78 and some others .95 i/p and .86 o/p ,97 and .85V o/p those with internal linking are nearer the o/p readings, up and down + probe to pin 1 ground then no forward drop reading to any other pin , max 2V IIRC on Fluke 77 Early Maplin in UK catalogues had pinning etc for a number of AY1- organ use series Tackling a functional replacement Wire a chopped down to 10 pin turned pin socket to the pcb and glue in place. Another chopped down socket , to plug into the first, wired to a piece of matrix board. Try an "upside down" ,positive ground (is that possible?) CMOS divider between Vdd and ground and voltage divided input signal to one of the CMOS inputs and and try just one output , level shifted with transistor and a couple of Rs , from Vgg, to drive any high level tone generators or whatever comes after. Power supply. You have to use the -27 volt VGG since VDD can be modulated. So a 12 volt or thereabouts zener, and a series resistor should be ok to get a -12 volt supply. Which will feed some CD4000 family chips, running upside down. Their positive power supply being the PMOS ground. Typical drain for the old chip is 3 milliamps, that should be plenty for a handful of CMOS logic running at audio frequencies. For each input, an input resistor, diode clamps to the CMOS power positive (gnd) and negative supply, and a schmitt trigger buffer or inverter. CD40106? Then use either D latches (4013) or JK ff's (4027) for the dividers. Easier to get the short divider chains than the CD4024 if you don't know how the external circuit is wired. If which edge is the trigger matters, you may needed to chain one of the spare 40106 inverters to get the right polarity to feed the flip flop. For each output, a small p channel MOSFET, source to (PMOS) ground, with a 6.2k ohm drain resistor to VDD. (Or maybe a jellybean PNP with a base resistor. Depends on the sound that results, perhaps). You might need a capacitor or RC filter across the output to slow down the edges.- Mark Zenier Euphonic Audio,amp 350,2001 Presumably a stock fault with these Euphonic Audio, USA amps. I'm having to replace all 8 of the 1/4 inch jack sockets. 4 of the 8 are totally breaking up inside. Assembly flaw - they used unreinforced plastic spacer rings on the bush inside the chassis, not dense fibre washers. The ring breaks and the bits drop away and owner tightens up the front nut, not realising that without the spacer then the socket is skewed/levered against the pcb and rear of front panel and the socket housing starts cracking up. Otherwise sturdy but now detrimental soldering of the pins does not allow any give there. The pins are joggle-formed to tightly fit double-belled eyelets and soldered through the board so as solid as can be, with base of socket tight to the pcb. It seemed odd to see a 555 in there for just a hold-off timer function. You need the same Ct/Rt values in both cases and one does not use a 555 The other pig with this amp , it uses that grey ribbon with soldered stranded wire cores that can only take a limited number of bends/unbends at the terminations before cracking. 4.7R, 38.2K,15R large Rs, NE555 2x 10N20, 2x 10P20 4x 0.1R, thermistor 2.7K in circuit cold Transformer internal fuse 130 deg C 3.7R//gn 1.7R 16.2V, Y 0.9R 14V, or-or 0.6R 110V LM393N Fender AB763 Super Reverb, 1966, 32Kg with added auto-transformer Loud farty noise , intermittently. Trouble was most of the time it was working fine HT voltages were 248V and 460V on main caps and 458V, 444V and 403V on B,C,D and 5V ac of hum on the main HT. USA 110V mains transformer was 1.6 ohm DC. 4 combined speakers was 1.4 ohm DC. When it farted then 192V and 363V on main caps , close to 0V ac on the earthy cap and 90V ac on the hotter one. Replaced with 2x 200V, 330uF in series, in line and protective insulation at the ends as longer than the original. -65V on negative supply. Also the 2 12AT7 were leaky so replaced. The original USA mains cable was perished and one of the "bright" switches needed replacing, requiring making a captive nut rather than tapped hole in switch mounting plate. So cured the main problems but the owner seems to live with what to me seems an excessive amount of stray mains interference, without any signal leads and input contacts shorted to ground. Blanked off the 110V outlet on the rear. This amp is 110V running off a 240/110 V autotransformer, neutral common, with the chassis having an earth to mains earth (UK). Other than probably something to do with the awkward cross-linking of the 2 sections of 2 7025, of normal and vibrato channels . It is possible to minimise the noise using one "normal" signal input and nothing in the "vibrato" inputs but the vibrato volume set on about 3 of the scale, not 0. Is there a recognised fix/amelioration of this effect. ? Removed the 47nF,600V "ground switch" capacitor and also tried a 55-0-55 isolation transformer feeding the 110 V transformer but no noise reduction. The only solution seems to be for a "clean channel" only amp by pulling valves 2,3,4,5 dealing with vibrato and reverb. Fender Champ, 1979 Probably model 5C1, uses 12AX7,6V6,5Y3 Probably 2 main valves dropped out and someone replaced the wrong one to each socket. Replaced with new and rigged up valve retainers as the chassis is inverted. Some light gauge expanded aluminium mesh that is used with resin for car body hole filling. Originally thought of deforming between convex and concave domes but could not find anything suitable. Settled for cutting some discs , hooking springs to the mesh and bent solder tags fixed to the chassis screws. Then pinched and flattened four "corners" to form a cap, looks reasonable. As a neater refinement, if a next time, I would upturn the edges and bend back on itself to form a neat rim and find some suitable dome shaped moulds to deform between. Some Transformer DCRs , forgot to note which was which 420, 278, 25 ohm (mains primary) Fender de Luxe, PR 246, 2004, 18Kg Only used , not abused, domestically, ie not bumped around ina van at any time. Mechanically broken dome end of GT badged Sovtek 5881, neat circular crack. Black deposit around a jet out of the envelope matching a black deposit on the metal "protection" cage screwed to the cab back panel. Gripper function around valve base was fine. Not obviously valve/cage touching, but close, I repositioned this cage 1/4 inch lower down and bent the horizontal part of the cage downwards a bit to give about 3/4 inch clearance from the bottles when no flexure of the back board. This model should have the plastic/wood composite back board braced back to the front as it has 2 large openings that seriously weaken it, but the speaker is in the way. Or a vertical bar from top to bottom to prevent the panel flexing inwards if pushed up against something. Large Rs 1.2K, 4.7K, 2x W/W 470, 4x 100K Fender HRD Reported fault/cur added here as aide memoire making a horrible buzz on the 'drive' & 'more drive' channels, as well as letting some sound through on the clean channel when the volume is at zero. Replaced 22uF caps - C33, C35 or C36 Fender DeLuxe Hot Rod ,PR246, 2002 Intermittant distortion The polished stainless steel control panel has the legends only silk screen printed on. No more durable than the white markings on valves/tubes. On/Off and standby legends already worn off. Removed this thin cover panel and fitted some 0.3mm thick celluloid over this panel. Form a right angle over a thin straight edge first and tightly bend returns behind each long side and cut holes through with a scalpel. R67 , at footswitch input, according to schematic should be 2W was 1200R, 1W , uprated to 3W Speaker 6.9R 240V primary 30R in cct P11 to p12 44r, p2-p6 7.2R, p5-p10 16R, p15-p16 4.6R o/p primary 80/107R to p18, Brn /Blue Bright switch only operates on clean , no LED, channel confusingly, it would seem. Reverb tank in circuit 55R, 206R Through AC voltages with 1mV rather than 4mV agreed near enough with the schematic as did cathode DC, NB use dummy load not the built in speaker, not mentioned on the factory schematic. Poor switch contact on the "auto" 4ohm / 8 ohm switch on the more complex wired speaker socket so poor feed to the normal 8 ohm socket also poor switch to ground if plug is removed. Beefed up as per Switchcraft in tips file. Replaced the valves. Fender DeLuxe, Hot Rod No reverb Failed coil on the output pickup of the springline reverb tank. Heat glue spots, unhook active spring from anchor and release gently for both springs and hold against the tray with tape. Remove 4 suspension springs. Grind out the brass rivet and later replace with brass screw and nut through the remnant of the replaced rivet. No need to remove the other rivet to release the soft iron pickup frame and thence the coil. Wound 2800 tuens of 45 SWG. NB safer to leave the rear metal gaurd attached to the back cover and so avoid putting long bolts in there instead of the 2 short ones. Fender Frontman 15G , 2002 ? practise amp Loud buzz and internal fuse blowing if replaced. TDA2050 supply rail to output 3 ohms, replaced. Grey insulator looked a bit suspect so replaced with mica but otherwise speaker seemed ok and no other reason for failure. Uses BA4560, 2x TL072, J111 FET 2x 470, 120, 2x .68, 2x 220 Fender PR466 Cyber foot controller,2001 No response to the pedal labelled continuous controller 14 switch and 2 pedal, midi output for amp. Used 9V dc supply, measured at only .2 amps so perhaps 300mA if all LEDs lit. Took apart to discover that the unit was outputting varying MIDI signals on all of the controls. The output pcb needs the retaining screws anti-rotation gluing. Negative pulse trains at a repeat rate of about 38mS ,only outputting pulses with a change of switch , vol or continuous pedal movement Fault on the "continuous" controller probably a case of RTFM From a Fender Cyber amp manual The unit is not responding to any MIDI continuous controller messages from external devices... Make sure the continuous controller numbers matches the value in the UTILITY menu or is one of the predefined numbers listed in the appendices. MIDI board just has 7805 , 2x LM358 PIC16C711 with 057127 v 1.0 firmware version mirocontroller and a 74HC00 for midi buffer etc. Other board , not seen, but probably just 4x TTL multiplexers , 3x 7s LED drivers and the display and no effects ICs. At least while in there dealt with the horrendous squeal from the foot pedals. Seems that for neutral hold, ie stays where the foot angle was last , relies on a steel sleeve inside then the moving and mount-steel plates, either side, and a through-bolt with nylock nut supplying enough pressure to make resistance to movement, as axle. But it is steel plate turning against steel plate on either side of the pivot - urgh ! Cut 4 washers from 1mm PTFE sheet and introduced between the grating surfaces after opening out the foot plate arms a bit. Fender PR559 Rumble 100, 2003 Broken guitar input 1/4 inch socket. Fender have used 1/4 inch switched sockets intended for domestic amp headphone use. Plastic bushes would be ok there but not where guitarists in full flight are likely to trip over or yank the guitar lead. Replaced with a beefier standard metal bushed, switching 1/4 socket fixed to front pannel and wired tip,pin,gnd,switch into pcb Opening- remove front grill, 2 side screws, handle and 4 top screws. Slide forwards enough to release the speaker/gixmo LEDs lead and then remove amp rearwards. One screw on 15 inch driver , near the tweeter, epoxied and maybe spiked anchor had grunged thread to hinder access. To invert the driver 180 degrees, for more balanced usage. Hook out epoxy with a dart point and pack out gap while unscrewing to avoid releasing the anchor, retap before reuse. Remove screws at rear of Ali, only, to remove the preamp board. Use thin card to keep the ali foil (beware sharp adges) in place while sliding the amp into carcase. Uses c3263, a1294, c4793, A1659A TL072,CA3080,BA4560 4 0.15R, 470R,47,75R 270,47R on preamp Fender PRO 185, 1988, 28Kg Getting excessively hot on the top over an hour total loss of volume, and no bass at any time. The 2 power rail zeners for the preamp had failed with age so over an hour heated up and rose from 16V so eventually exceeding the rating of all 8 of the same batch of Motorola T072C dual opamps. 2x 1N5353B 16V,5W replaced each with 3x5.1V large 3.5amp zeners in series and all T072C replaced with TL072C. Running with the speaker the large .22 ohm speaker line dropper fell off the board. This had been repaired before apparently but whoever had replaced with no allowance from the brittling of the work-hardened leads . Replaced with stout pins to the R and anti-vibration silicone rubber pads. Uses 4x MJ15003, 2x MFE15030, MJE15031, T072C, LM339 Motorola MPSU10 plus another of same low format maybe MPSU60 marked PSU60 2x270R, .22, .1 large thermistor 2.2 R cold 2.2K,3.3K,2.2K,1.8K,2x 47, 10R Thermal sw N/C 248 deg F ? = 120C ? The J111 NJD FET is 20 ohm and for the main supplies +/- 49V some voltages with no load on o/p Q11 -.64,1.1,-1.2 Q15 1.1,49,.56 / Q16 -1.2,-49,-.6 R177 -14.2, -15.6 W12 -15.6, W13 -14.1, W14 14.8 W4 -14.5, W3 ? +/-? 14.5, W5 -15.6 W8, W10, W9 -15.6 40 minute dummy load test (after 30 minutes the temperature stopped climbing) metal encased thermometer laying on the heatsink settled to 68 deg C. 4 ohm dummy resistive load with 1KHz sine source and amp gain adjusted to give 9V rms on DVM capable of 1KHz monitoring , about 20 watts, into the load. After about 30 minutes although the power out was still dropping it was very much slower than from cold. V rms over the load dropped 10, percent so equivalenmt power out dropped 20 percent. I don't know if this is too much or normal but I would want the output to drop over an hour rather than rise. Anyway it was satisfactory to the owner. Fender Pro 185, 1989 A later case of same problems as the one above. In particular the large R that is common between all 4 Re and the black thermistor or whatever (cold 2.5 ohms ) in the mains line. With all controls anti-clockwise bangs. To avoid mangling the ribbon interconnect, wrap the cables to the springline around the subboard locked onto the main board. The zeners were not causing a problem (yet) but added a "M vane" heatsink to each of the two zeners that caused problems in the other one. Some strips of shimstock bent to form an M shape and held by removing the diode and settling the centre of the M underneath and a snug fit around most of barrel with thermal compound and heat resistant glued to board with dimensions/position so that if it should move then would not cause shorting problems. Also raised the 2 droppers off the board with varelco pins. The 2 paralleled speakers measured 3.4 ohm DC. Did the following with all 4 of the largest Rs and perhaps they will survive better than the original coppery leads failing. I'm assuming the oscillation mode is transverse to the resistor axis rather than axially rocking. If laid against the pcb then the ceramic "feet" act as leverage when rocking and if elevated off the board then extra momentum also amplify the rupture force at the point where the leads go through the board. This is my latest attempt. I have hundreds of these hermaphroditic Varelco, Elco, Edac (DERA company, over-shelflife disposal) like in pic http://www.dhaen.org.uk/vdocs/Onryoku2_files/varelco.jpg (in the bag ) I could find no other pics on the net. The flat part is the mating part so they can mate like 2 fingers of one hand rotated 90 degrees and mating twith 2 fingers of your other hand, so no male/female specificity. A pair of these gold plated brass contacts with one of the 2 fingers cut off with snips . Matching side with side so when crimped and soldered to the resistor leads , facing opposite directions, they are, locked against rocking, against the board. It will still be a weak point at or in the pcb hole but will they be more resistant to fracture than the usual resistor leads metal ? On opening this amp there was a smell of hoese manure. Compare with JBL amp on the other repair file. Different company , different function of amp , but both made in the USA. Trying to investigate this with the help of an organic chemist it may be Hexanoic acid or Caproic acid but is it a biological breakdown, age deterioration, overheating or burning of shellac or phenolic insulation. ? Anyone any input on the chemistry or any other examples ? Butyric acid, smell of vomit, is another such breakdown volatile organic chemical that may be relevant in similar circumstances where horse-glues or leather or insect derived resins are involved. General Instrument AY-1-5050P replacement Pinning in 1982 Digital D.A.T.A and similar logic types for organ use MM5554,MM5555 MM5556,MM5559,MM5823,MM5824,MM5832,MM5833,MM5837, MM5871,MM5891 in National 1977 MOS/LSI Geni Electronics RL3 075A Disco Strobe No flashing but with no room light could see a glow in the connector of the zenon bulb crackling and burning smell and smoke. Connector made of bakelite looking like a Bulgin connector. Sequence probably poor contact between socket and pins leading to arcing between the 2 pins carying the 400 Vand heating leading to carbonising of the bakelite.between these 2 pins. Removed bulb and powered up and no arcing. With a small ball mill and dremmel milled out area of charring leaving an air gap hole thru the bakelite between the 400V pins. This problem may have been long-term the problem was no oscillator function. All 4 outputs of the 4093 were stuck high. For bench testing power up with 11V across the 12V zener diode. Hacker AL 42 (second channel to a GP 42 ) 1968 Used as a guitar practise amp. Severe buzz 10 minutes after switch on. Badly worn track on the vol pot. Dismantled and renovated. Hartke HA1200 Broken input socket soldering due to tripped over lead. Had to reinforce the tracks on the pcb but as another one missed decided to replace the CH2 socket with an upside down chassis one wired in, just in case . Held needle to pin 3 of the 4025 injected signal but not at the jack input. Remove 4 outer bolts inside heatsink and 2 on pcb to remove rearwards from casing. Uses 3x 2SC5197, 3x 2SB688A (C/E "diode" checks 0.53V on all) 7815,7915,4x 2058, 2x 072, 2SA1659A, 2SC4370A 6x .47, 2x 6.8K, 270 thermistor 347R in circuit, NTC Vs on non signal connectors right to left 48,0,48 V ac 18.5,0,18.5 ac 0.24 over 6.8K 24.3, -19.3 ditto -19.3,-64 270 .55,-.35 one 10R -24.1,-24.3V Dummy load test of 400 Hz giving 8V ac in 8 ohms Stabilised at plus 23 C over ambient in 25 minutes , thermometer resting over fins, 8V ac dropped to 7.8V To remove or replace the amp without dislodging the captive nuts or tearing the metalised card screen it is necessary to use 2 steel foot rules or similar and release the 2 top corner protectors or hack back. And pierced gaffer tape over each of the captive nuts as belt and braces. Hartke HA3500 , 350W, 2004 Not being overdriven just failed in mid song and replacement mains fuses keps blowing. Mains transformer 2.5R primary and 2x 0.6R main power secondary. The 100n , 200V polyester cap had failed to dead short, replaced with 630V one as plenty of space with a bit of rewiring into the vacant second bridge area. The only marking is 104J 200N no mention of ac or dc so could be 200V dc, maximum dimensions about 8x10x4 mm. I expected the problem to be near the pins which are about half way along the foils, staggered for the pin spacing. Problem was buried in the assembly about 3/4 into the centre, a number of sputtered/fused layers but no smoke emanation. There was localised micro ruffling of the foil in that area whether cause or effect of localised heating , I don't know, but the ruffling extended the width of the foil, not just the small "spot weld" area. 3.15A mains fuse ok on this amp, not torroid. Thermal sw n/o. uses 2068, 5532, 4558, SSM2018, M5227, 072 7025 valve (don't know where the HT is derrived) TA731? (obscured), as in 4x complement side of 4x 2SC5200, 2SC4370A, 150R,15K , 10R PS uses 22, 3x 10, 56R 125V ac over main bridge, +/- 84V other ac secondaries 6.7V, 11, 24,0,24 Load test with no top cover so no fan cooling ( directs inward). 4.5V ac over 4 ohm , with thermometer laid over the bodies of the top power transistors. Took 35 mins to stabilise at 65 deg C over ambient down only 5mV or so HH ( H & H ) Echo unit (Tape loop), 1970 No echo Two of the 1970 741s had at least one I/P at rail level HH Electric cabs The fuse holders use a cap/closure that is larger diameter 10.8mm and coarser thread than usual 20mm fuse caps HH L50 50 series, 1986 During break in light use , internal fuses blew. Also ch1/ch2 select is fine with added footswitch but temperamental on its own, due to dirty contacts on the 1/4 inch socket. With speaker (3.8R) soldered in about 5 and 8 ohm across the main DC rail caps. Both TIP132 and TIP137 power darlingtons were low ohmic "C/E" Replaced with added heatsinks as no venting and signs of long term overheating, cream and dusty thermal grease under the transistors and slight local pcb discoloration. Added 1 TO3 type heatsink on the mounting bolt of each tranny. 1 3/4 x 1 3/4 x 1 inch , 20 vane type , projected 1/4 inch out the rear of cabinet. 2 more retaining bolts and bent middle sets of vanes to touch for more robustness as well. Don't know what previous load test results would be but this for thermometer over the 2 heatsinks and inbuilt speaker. 80 Hz producing 0.1V ac on line out and 3.86V ac over speaker, cabinet surrounded in wadding. Stabilised at 16 deg C over ambient in 15 minutes and dropped 0.05V ac. Uses 150R, 2 x <>0.3R, RCA 1C03-C, RC4136, 2x 4558, 2x330R Without speaker "C/E" measured "diode" test .5 and .47V "C/E" on TIPs Still no speaker and no signal, 24V ac on each fuse +/-33V on main interconnect lead. 1C03 measured -39,-3.9,-31.6V HH 100W monitor, 1975 Excessive hum and reported , but not induced, low level noise problem after an hour. Remove the 2 machine screws at rear panel and 2 on the side of the control panel to remove the electronics. To get to speaker , presumably prize off the front grill frame. Hum due to lack of screening between toroid and preamp. Just placing a hand in the gap would significantly reduce the hum. Even just a finger in line between core centre and IC1 would make a noticeable reduction. Fixed a mu-metal screen between which helped but had to screw an aluminiul plate over and down one side of the Transformer / insulated from the back plate, to near enough cancel the hum. FT5415 seemed too hot even with heatsink and replaced with 2N5415. Reduced the I/P resistor on high I/P from 330K down to 30K. Voltages at ZD1 and 2, +-16V Uses 2 x .33 , .1 , 15 ohm wirewounds 2 x 2N3773, 40872, 40871, FT5415. HH MA100S 5 channel ,stage amp, 1975 On penultimate use distortion at high volume. Then last use, distortion like power-down distortion, at any level and tinny, no bass sound. The TIP29C diode test Vbe and Vbc was about .8V and discoloured printing . The TIP30C was about .55V so replaced both with TIP41C and 42C. Other Ts 2x 2N3773HG,BC204,BC207,2N3440,FT5415 and 741CS op amp. Power rails 46,-46V Repaired handle a la tips files. No bass was pot corrosion problem. To gain access to that area remove knobs and perspex. Desolder the nasty phosphorescent panel powered directly off the mains. Amp can be set for 110V mains but this panel needs at least 200V to light up it seems. Undo the pre-amp retaining nuts and then there is enough space when this board is propped up to pull each pot out to rennovate. Mark each pot 1 to 17 as rather vague wiring loom. Considered replacing the luminescent panel that was flaked and partially working. Could try computer case type electoluminescent panel or even EL string looped around each pot shaft. The best solution would probably be a pair of cold cathode tubes and inverter off 12V dropped from main supply. HH MXA 100, 1986 Reported as master vol control pot broken as intermittent breaking of output on touching Actually corroded/grimy bypass switch on the send o/p 33,33V ac , to +-44V dc uses 4558,071,RC4136, 2x 3055, RCA 1C03 2 off, 1Co4 2x 690 ohm measured in circuit 2x <>.1R, 2x 10R, 150R HH Performer amp ,150W, 1980 The effects plug-in of delay and phaser not working. The -15V rail missing due to an overhheated mess at the ps and a blown resistor. Replaced each of the 2 2W, 30V zeners with 5 seriesed 6V, 1W and the much larger 330R W/W. Can't be sure the other zener droppers were 3.3K as charred MO 1/2W but replaced with much bigger 3.3K. The pedal din connector needed replacing , beware of the bridge internal connection touching the din closure screw or the function plays up. Beware exposed springline is behind ch1. To gain access remove front 4 and rear 6 screws. Remove front panel and rotate to pass back through the casing and remove both front and back. Hold , for working on, with 4 tapped rods no more than 9 inches long so one panel can be reversed to work on. +/-58V, +/-30V rails On the plug in uses 3x HH badged CC100D (bucket brigade ?) 2741 M7815 and 7915C and Vactec VTL5C LED/LDR optocoupler. 2 bulbs were 16 or 18V ,.4A main boards use 2 bulbs 24V,1W Large Rs 2 x 330, .1, 2 x 330, 180 with diode 2R2 and 10R. ch2 620, 680 and ch1 1.5K MosFet HH HFN and HFP probably replaceable with 2SK135 and 2SJ50 2N5415s, MPSA42 and 2741 on ps Hohner Stereo 50, 1978/1988? Loss of external channel Uses 2 pairs of TDA2030. Bad solder associated with one pair of 2030. Added a switched 1/4 inch socket in the line of the integral speaker so both speakers could be used powered from another amp , as insurance. HK Audio, Hughes & Kettner, L.U.C.A.S 600, 300W sub woofer and 2x 150W outliers The vol knobs are not recessed and very exposed , underneath, for bad handling over the tailgate of a van, so stove-in, needing the pots replacing. Nothing wrong with these 2 mystery 2 pin items, but I like to identify such mysteries and place on the www. On powering there is only 7mV over this small blue blob that measures 58 ohm but looks like a tiny ceramic cap in the fan stream In the fan air-stream a 1.5mm sphere I assumed to be a bead thermistor , measures 58 ohm, in circuit, but no change with freezer spray. Blue bead with a white letter H marked on it. 2 off per channel amp, black epoxy potted lumps, about 8mm cube, with a large white letter M on them. Measure about 150 ohm , in circuit, and no change on freezer spray With the bead one, thats what I did first, but only held between fingertips, usually shows change and + or - . I will retry with a nearby soldering iron on Monday. My thinking was tiny bead thermistor would be far more responsive than disc or rod but maybe very insensitive, any chance a humidity or velocity sensor somehow ie in use it is heated? , will have to try powered up Black cubes are in fact 4 lead, 2 from the top and down the side and 2 underneath LED/LDR couplers LT3011 The fan blows out so this track-side mounted component is not so obviously in the airstream now, but no reason why it could not be mounted component side other than maybe too near a pair of W/W droppers. TR3 is the preset not this blob, which is unlabeled on the board and overlay views, but seems to be the PTC thermistor ? on the first image in that pdf, labelled R84 setting the FET DC for the amp input. Can thermistors go wrong ? Placing a 700 degree F soldering iron tip 5 mm or so under this bead changes the resistance from 58 to 66 ohm, ie swamped by the 2K2 resistor so totally ineffective. So is PTC B59 80C some sort of miniature 80 degree C Woods metal thermal fuse, if so why is it not near a heatsink, or is monitoring general air temperature good enough? If the fan stops then this sensor is nowhere near any heatsink and would be monitoring fresh air being consequently convected in through the fan port which is just plain daft. I returned to freezer spray on that blob, with a 1mm bore tube this time added to the spray can. NTC , going up to 100 ohm . And in case it was due to the spray movement I wrapped the blob in cotton wool , confirmed NTC below room temperature, so a very odd characteristic. The blob should be nearer a heatsink , rather than the fan. The whole air handling system is in a duct so it could be anywhere for monitoring internal air temperature , but directly over the fan is not where it should be. If the fan stops then cool air would be convected in there, falsely telling the control that the amp is now cooler, and would accelerate the already hot amp to quick destruction. 32-0-32 V ac uses AE123 4x MC33079, MJ11015 , MJ11016 2x BD238, in cct Rs 405, 410, 3x 0.22, 180, 470 MC33078 on middle amp Hughes & Kettner Attax 80, 1993 Worn pots, long bushes , so reconditioned existing ones. Elbow speaker plug needed attention (see tips files) Uses 072,082,081,1538,4053,NE5532, MJ4032, $035 Rs 2x680, 2x 1k2, R15, 2x R.22 ? , 180,470 Jem Fogger smoke generator Failure to start warmup cycle Break in the lead between body of m/c and hand remote,this lead was 6 core ,5 only used ,so paralleled the sixth to the errant wire. JSH Encore guitar Physically broken vol pot and because no anti-rotation nibs on any of the pots they can rotate and have pulled and broken all the wires except a very twisted ground wire. Replaced the grounding wires between each pot with some rigid copper strip to stop chance of rotation as bush nuts are only tightened against the fascia, triple lamina plastic sheet ,used for sign making with a pantograph engraver, i forget the trade name. Unless they're (Wind/Reverse Polarity )=RW/RP to reduce hum, which is pretty standard for most Strat pickup sets these days. Hold the magnets up to each other to check the polarity (top of one PU to top of the other PU). If they're RW/RP, then the two that repell each other go in the bridge and neck positions, and the one that pulls towards the other two goes in the center position. If all the pickups repell all the other pickups, then they're not RW/RP. Electrically all 3 measure the same about 5.03 K ohm and 3.26 Henries each. All 3 pots are 500K and one 47n cap in the filters section to ground and common of both tone pots. Output about 400mV pk-pk, one string. Resistance check for single pu , turning vol , from 0, to mid-500K, to 5K. The problem was finding a short shafted pot of 500K, the one I found to replace had a central detent which I cut off. Switch positions 1 pu farthest from neck, 2 mid pu, 3 neck end pu 4+5 o/p, 6 n/c,7 to lower tone pot wiper, 8 to upper tone pot wiper Only one or two large coils in each pickup. The exception being the hex pickups used in guitars that drive synths or midi controllers. In those, there are 12 coils one humbucking pair for each string. Typical pickups are either "single coil" or humbucking. Single coils are simply a few thousand turns of 42ish AWG guage wire around the magnet structure, often individual pole magnets or ferrous poles with a magnet on the bottom. The humbucker is made up of two coils counter wound and magnetically opposite built into one body and wired in series. A pair of opposite-wound pickups would tend to cancel a magnetic hum field in the transverse sense, parallel to the neck, as well. Kay Sound Fashion Gold State Amp Totally dead amplifier Severe corrosion on the two board mounted 20mm fuse-holders leading to break of contact.Replaced with new 20mm chassis type holders. This amp is the same as Sound City SC30,2N4033 is an adequate replacement for the SF118 and BFY51 for SF128. Kay 50L, Kay Sound Fashion,1983 2 KD606 power trannie DC voltages 42,20.9,21.3: 20.9,0,0.33 Kef Kefkube 100 equaliser PS input marked as 23V AC but needs 23-0-23 V ac as LM317 and LM337 are set for +20V,-20V Korg PSS 50 programmable stereo sequencer Failure to latch change of pitch selected on the keyboard and also 2 adjascent keys giving the same pitch change. Battery corrosion in the battery compartment had caused corrosive vapour to attack the PCB tracks and 3 of the front pannel click switches so even the 2 internal through connections in the switches were corrupted.The click switches have an unusual length of stem so a matter of cutting the 4 retaining pips on the old switches and the replacement switches and swapping over stems and gluing,also beware of turning over the top panel with the top PCB unscrewed as all the plastic switch inserts are not captive and will fall out.Also an intermittant open circuit 1N4148 type diode on the switch pannel was causing malfunction and cross-coupling between the number switch pannel and the pitch switch pannel. Kustom KGA10FX practise amp Intermittant loss of all including power on LED Loose spade connectors and poor solder on a W/W Transformer marked 22.8V ac, 250V/5A/130 degree C thermal fuse , measured 2x 11.7V , no signal Uses 7805, 3x 4558, PTC PT2399, TDA2040, 0.1R. V on 330Rs 14.7, 10.2 and -10.3,-14.8 1R 5V, 47R 13.7,14.7V Kustom KPM6160A mixer amp from 1997 intermittant crackles and sometimes loss of sound, waggling the interboard ribbon leads produces these symptoms. The .156in spacing Harwin/Molex/ Amp/Tyco connectors for power are fine , 2 sets of crimp pairs , one crimped around the conductors and one crimped around the sleeving. But the .1 ins spacing ones have single crimp pairs which are crimped around unstripped insulation and relying on the returned ends piercing through the insulation into the conductors. I pulled the wires out, very easily and cleanly, cut the ends off , solder blobs on the pins and the recut wires and soldered together. Some "hot-melt string" melted over the joins for some mechanical bonding to the shroud. I looked closer to the crimps and the returned ends are curled over where they pierced the insulation. The interconnect in the mixer section , .1 ins spacing was properly crimped, so just the ones between mixer and ps and ps to amp were bodged. Instead of 2 sets of crimp points - one for the sleeving and one for the conductors. These ones had one pair and instead of stripping back the insulation and crimping to the wires, they had not stripped back and crimped hoping the returned ends of the crimp tangs would make contact with the strands. Often seen with those small crocodile connector, jump leads, that you get in packs of 10 , 2 of each colour. I long since learnt with them is, when you buy them, the first thing to do is you pull back each croc and solder the wire to the croc. The heatsink insulating pads had shrunk, probably excessive heat, leaving a crumpling on the uncompressed areas, but all in working order as a pa. Replaced with mica washers. Previously took 50 minutes to stabilise at 33 deg C above ambient pumping 9Vac of 400Hz continuous sine into 4 ohms. Dropping by .35V ac over 30 minutes due to temp sensor presumably. With mica replacements, down to 30 minutes and you could keep your fingers on the body of the trannies, too hot previously. The pads may have chemically failed , but even then , mica does not degrade over 10 years. One of the 12V regulators had been broken/dealt with by a previous repairer , all 3 need protecting as very exposed. Uses TA7317P and NE5532 1.5K, 2x 220 on the ps 2SA1943, 2SC5200 x 2 , LM35DZ temp sensor (LN33 on the overlay) 2SA1837, 2SC4793 (All o/p devices 110 ohm B-E measurement) 2x double.22, 2x 10, 2x 47K , 10K, 2x 100 on pa R21,R22 = 10R overheating marginally , should use 1W Belton BSN2EB2E1T springline (210 and 62 ohm) Main power ps connector -48,48,0,.24 (it was 24 deg C room temp), 0,0 16,-15V to mixer AB Landola semi-acoustic guitar electrics ,c 1960s I worked out how to remove the electrics through the frettedwork, all sorts of minor problems in the wiring etc but main one is no signal from one of the pickups. One pickup measures 7.7K and the other megohms There is some useful dating info on http://www.landola.fi/dating_your_guitar.html but to get it tighter the pots are 4 off 250K marked Prem (looks like) and a 4, along with the 250K stamped into the monkey metal is the number 437. Unfortunately 4 off the same pots so don't know if a type number or week 37 of 1964 . This one has serial number in the 109 thousands. caps are marked ERD FOL and 2 vertical lines like mark 2 I trod carefully and ground through the solder on the rear of the pickup with a Dremmel. Just as well as the magnets are directly over the brass. Chromed cover plate removed. The output screened lead goes into the tissue paper, lower left http://home.graffiti.net/diverse:graffiti.net/landola_pu1.jpg looks as though no varnish /laquer and and just wrapped in tissue paper but light hooking under does not shift the coil. Would it be glued underneath , unseen? Surely it would not be loosely laid in there with just compressed tissue paper holding it in place. Turned out it was lacquered in and so defeated counting off turns. Very thin bakelite (the pinkish colour trough) so must be incredibly fragile 45 years on. The paper and coil was lightly laquered in, not as obvious as magneto coil. With child's toy wooden clothes peg, one wedge of, and small plctrum managed to ease out the coil with only minor collateral damage to the wire and no damage to the bakelite (will have to chemically clean oput the glued in paper). Taken dimensions and weight to 10mg so should be able to rewind another. Looks like bad assembly, in that in the process of wrapping the tissue paper strip around the coil , the lay had been seriously disturbed and then probably vibration/thermal changes/chaffing enough to make a break somewhere. From the owner the odd woodscrew is for a now missing finger/scratch plate. This is a 12 string version http://www.hagstrom.org.uk/Other/Landola12/P1000606.jpg of the same guitar, the one I have here is a 6 string, deep cherry colour version and tremolo arm. After 1961, before 1973, the serial number 109,000s could put it in 1964 , according to "437" on the pots and roughly mid 60s via the hagstrom dating file. Any idea of the pickup make? owner thinks Ibanez. No name/numbers found on /in them, Landola own ?, the ones here look identical to the ones on that 12 string version, offset slots, chrome cover, black bakelite base, screw positions etc. Exactly the same fretwork , so quite a chinese puzzle removing the 2 off paired up pots and brasswork out through the slot. The same "crackalure" evident on the top face of the body in that pic pic I took , before tying back the internal wiring http://home.graffiti.net/diverse:graffiti.net/landola2.jpg http://home.graffiti.net/diverse:graffiti.net/landola3.jpg With some Pekalit red bakelite and brass knobs I have a supply of , far more in keeping than the "original" ? aluminium Japanese ones. Trough for the winding hank is 56.5x3mm to 70x14 x 6.4mm deep. The rewinding former has to be demountable. A plastic booklet binder spine warmed up and opened out to a flat bottomed slight V and then gripped with small square rod and heated again to form a steeper V section. Round all exposed edges. Doubled up 60mm long, end over end, and 2 cuts per side deep into the V sections , so can easily cut the remainder after winding. A small piece of metal tube pushed through the binder spine to mount in the coil winder. Otherwise fine wire coilwinding dealt with on my tips pages. Some thick PTFE wound around to decrease the width a bit to match the trough dimension, some thin elastic laid across , so under the wiring, to tie together in loops after winding. Then some thin PTFE over the sides so nothing to catch the wire. To join 0.05mm wire to intermediary 0.5mm wire (will work for 0.05/0.05 mm join), strip varnish with lightest of touch with Dremmel grinding disc. Grab the ends with a toy wooden clothes peg and twist. Coat with solder paste to solder, and a small dab of hotmelt string for more mechanical strength. Another not so obvious tip for winding such fine wire, cut your fingernails and sand paper , so nothing to catch , and good lighting. More "ghost cocoon" elastic spiralled through/round the hank before setting in the trough. Lacquer in place , including the elastic. 125W soldering iron to remake 6 solder points of the brasswork, such indirect heating of the wiring made the coil resistance increase 500R. Beware of the signal screened cable comeing out between brass sections, not through the hole underneath or the pickup position will not be adjustable due to fouling under. The original one probably failed because in the process of wrapping with tissue paper and adjusting to fit into the trough , the layup was seriously disturbed/ stressed, before lacquering. Removing the brasswork ,holding the pots. Undo the 3.5mm sockets , but leave pots in place. Turn so pot shafts poke through the large hole and end circle, then angle so one pot comes through the large central hole, then angle down the slot to remove the second one 1, 250K 2 250K 3, 470R 250K pot 4 47K, 250K pot 2 C 0.022/10/400 150V, 50Hz If re-using the original steel woodscrews, grind off the rust as turning to undo broke the flimsy small edge of the black bakelite pickup surround, used hotmelt string with copier toner included to "repair" Using a 390uH wireended axial choke for injector in place of guitar string and an AF generator and comparing roughly the frequency response. The rewind was about the same at 100Hz , less at 1KHz and more at 8 KHz Laney CD850S, 2002 2x 200W mixer amp Problem in protection (falsely triggering occassionally), both amps dropping out. Of course I have not been able to induce activation. Remove 4 feet screws and 3 screws from each side to remove the full metal case interior. 2 separate power amps otherwise apparently the same , both carying output DC protect and overheat protect output relay drive ccts. But only one normally open thermal switch going to one amp only so only dropping out that relay and amp only with no interconnect to the other amp. More likely a problem with the thermal sw or 12V supply to both protection cct and the fan , rather than a fan problem as it did occur once at sound check and once at switch on. The fan does stop when this happens so unlikely a send/return bypass sw problem, the monitor outputs still continue to work so not a mains failure problem. There is also a thin low current , signal level earth wire from the ps that had come adrift loose in the case , broken at some pcb solder point presumably, somewhere indeterminate from the schema. Yet again bits of hardware, 2 bolts that hold the heatsink to chassis loose and wandering around inside the case, but probably just incidental to the main problem. I checked the switch in a can of water and it goes s/c at 86 degrees C and reverts to normaly closed at 71 deg C and no amount of knocking will disrupt it. Logo - C followed by 2 square wave pulses KSD301 K85 probably (smudged) So the 85 means 85 deg C and perhaps K means NC Bit low for a 2x 200W amp even if fan assisted cooling but as nc operation means its immune to false triggering from contact corrosion I will leave that as is. The unusual mustard yellow items that look like disc ceramic caps in the ps are polyswitch fuses, marked T60 090 are 0.5 amp and 2 amp rating according to the schematic . I added a 90 deg n/o thermal sw to the empty socket of the other channel bolted to the underside of the heatsink. Just a signal diode connecting the existing thermal sw to the same pin on the other amp , empty socket, would have coupled both together but I added a higher temp switch instead to allow half-cock continued but still protected use on one amp should the other fail. The rest of the protection is to protect from DC at the output, functional in both amps. I accidently activated this by powering up with one of the wires from the main bolt down bridge rectifier disconnected. The stray low current wire would seem to bridge back one side of the ps to the other , on the same board, when they are both connected to main reservoir cap common via large traces anyway - there was a lone socket pin in the housing with matching frayed wire taking power to one amp , the other end was with the power connector for the other amp. I also replaced the 12V fan, with a 0.1A ( original unnecessarily overworked one 0.2A) as worn and wobbly and more to the point, fully cut the casing open to give 5 sq ins vent area at the fan vent and covered with a wire grill. There was just 14 small slots with a combined area of only 1.5 sq inches, let alone vortexing, so overloading the 3 inch diameter fan with through ducted area of about 6 sq ins and so losing cooling efficiency. Replaced the 12V regulator just in case. For the protect ccts, when in protect mode the voltge across the base resistor of the relay driver pair was 0.02V and .64V at the base and 0.76 V on the 12K resistor In normal operation 3.6V across base resistor, 1.26V on base . Long term problem in one amp leaving one Re o/c so on that power tranny the B-E "resistance" was 109 ohm instead of 94 ohm measurement on all the other 11 trannies. Running lower amp (right) only and 8V , 400Hz (16W ) into 4 ohm load with thermometer on the heatsink. Stabilised to plus 17 deg C over anmmbient (with this .1amp fan) after 20 minutes and .02V ac drop in output. Star washers and high temp glue on all internal bolts and hotmelt glue on the connectors, especially the small ones associated with fan and protect ccts as little friction keeps them in. Laney CD850S, 2002 Same as above plus broken effects 16 way Hex codeswitch, all plastic Replaced with a proper metal one but greycode so 1 to 16 became 1,2,4,3, 7,8,6,5, 13,14,16,15, 11,12,10,9 Laney CK165 , probably 2003 combo Buzz reported as pitched at a G an octave and a fourth below middle so 100Hz. Both ps caps had oscillated to the point of breaking the glue bonds. One had broken the trace and the other had an internal fault. As could not find a sizewise replacement and as very cramped anyway plus would have to tie them together to (maybe) avoid a repeat. Replaced each with a pair of 10,000uF, 35V with 12K balancing Rs, bolted to the chassis between prea and pa. Uses SAP15 PO and NO, +/-49V 2x 560R, 3x 3.3K, 2x 10R, 2x 0.22R ribbon 15,-15,0,sig,0,49V No name elbow speaker 1/4 jack had a loose barrel. Undo th e2 screws , find a large nut that the tip will sit in comfortably and squash , firmly held from slipping, between tip and the central connection to squash the barrel back to the flange. Laney GH50L, 1994 noise problems, crackly (pots) and rustling (valves) 4 presumably ECC83 (not originals) all test bad C/H leakage and bad/ low or marginally good gain. Not a trace of any marking , as low power valves, presumably no marking originally. They look like any other ECC83, no bad cut metal/ broken mica or any other indication of bad manufacture. 5 controls needed seeing to gain,drive , master, bass and rear FX pot, and seized knob grub screw dealt with Laney GH100L noisy replaced one ECC83 and 2 gain controls Laney L20H, 2007, PbF, valve amp Intermittent loss of output and crackles. Side-issue on polyswitches/ resetting fuses Mustard yellow about 20 x 15mm , looks like a silver mica cap, but round leads. In line with about 2.5 amp valve heater line. Measures less than 0.1 ohm , apparently invariant to nearby soldering iron. .Letters China, 30, UF 600, GL WE, polyswitch resettable fuse , like http://www.datasheetarchive.com/download/?url=http%3A%2F%2Fwww.datasheetarchive.com%2Fpdf%2FDatasheet-052%2FDSA0059269.pdf previous one I saw was marked UF250 and was about 8 x 8mm so not definite indicator of rating, presumably that one had a 20V rating , on a 16V supply 30V rating and that Raychem series then package size goes with hold current UF250 about 11x18mm, hold 2.5amp, long term trip current 4 amp UF600 about 15x20mm , hold 6 amp, long term trip current 8 amp UF900 ,the highest in that table 22x28mm , 9 amp hold, long term trip about 12 amp. Some other polyswitch details 19.5mm marked logo of V over upturned V 72, x250 HIQE China or EVAE Mexico 2.5 amp hold current , opens after 80 second with 4.5 amp, > 3 min at 3 amp 7.5mm , logo B for maker and part BRN MF-R110 marked R110 5078S 1.1 amp hold current Actually extensive PbF problems and poor 1/4 spade connections, particularly at the choke. Access - remove 2 rear pannels, 2 top screws, invert and then 4 side screws. Chassis not fully baxed so can tip over. 3 non pointed screws on rear cover To get to the reverse side of the main pcb which has the sm hidden TL072 opamps etc leave fuse holder and remove the speaker outlet board. Angle the pcb over the fuse holder , then pot array past the chassis rim, leave wiring in place. 10K, 56, 470R 2x 100R 1K reverb measures 220 and 30R +- 20V over 100R 264V,255V over 470R 255,220 over 10K 8.5V on 56R Handle needed attention and mod, leather over cloth . If the metal sections open out then the cloth can slip through the gap and the leather stitching fail , so handle collapses. Open out the metal to slide off, slide on a nylon tube about 3/4 the whole gap length , then the end of the handle and then close up. The metal would have to open to a 1/4 gap before the nylon could slide off. Laney LC15R, 2002 Captive nut loose in the chassis blowing fuses etc Blew one of the HT diodes and mains fuse Some DVM resistance readings speaker 5.7R mains primary , 240V, 52.5R secondary 206/19/19/188R heater secondary 0.2R without valves o/p transformer 104, 114R/ 0.5R Laney R4, 2003 Bass Amp combo, 32 Kg, distorted breaking/muffled output, the distinctive sound of complementary output failure of one waveform component, the positive or the negative going one. First thing to say is anyone finding one of these, put some fine mesh under the top grill which lies directly over the power amp. Kids like posting coins into slots, even TVs of 40 years ago had such mesh under the ventilation slots. Perhaps block off totally and add a vent or 2 at the sides as there is no sides or top to the amp chassis. A small piece of copper wire had dropped in this one touching a couple of MPSA92, and half blown the amp. Uses 2 pairs of 5 pin SAP15NY and SAP15PY output devices according to Sanken datasheet , in English, h1-o03ea0-TR.pdf 150W, 15A, 160V bipolar with temp compensation. There is another major flaw with the production of this amp. The 4, 0.22 ohm ,emitter resistors are on end and one end soldered right down to the board. Not failed soldering so 5W must be the right rating but vibration is causing the resistor lead to progressively fail at the juncture of the component side of the pcb and the flaring , over the lead, of the ceramic covering of the resistor. Replaced each with a pair of 0.1 ohm with a pair of ceramic beads flat side against PCB and temperature resistant glue holding in place. As well as a mesh under the grill , cut an aluminium sheet to form a sloping cover over the amp (so you can tilt up the whole amp to slide in and out of the wooden housing). Extended the 2 long stand-offs , leaving a 38mm gap to the aluminium , and made brackets to fix to the heatsink screws. Covered the leads to the thermal switch. All nuts and bolts glued in place. Laney R4, 2002 Came in for replacing one of the input jack sockets. Used a chassis mount,gold plated, wired tag one upside down and cross-wired in. 2 of the output emitter resistors were neatly loose, one for the N and one for the P sections so output halved if he'd realised it. Used 4 pairs of .1R and soldered eyelets to beef up the standoffs and plaited some silicone sleeving to make a rope to tie all the twisted lead joined Rs together tied down to the board. Laney R4 , 2003 No output Failure of 2 transverse set emitter Rs so one pair of devices still operational, not blown due to overloading. Bad solder on one of the main dropper Rs Laney R4 , 2003 No output, Failure of 2 transverse set emitter Rs so one pair of devices still operational, not blown due to overloading. Bad solder on one of the main dropper Rs exactly as the one above The pair of emitter droppers width-ways across amp had failed. Replaced with series pair of 0.1R with loop at top and twisted rope of twisted triple of PTFE as restraint. Tx 3.9R // .5,.5 / .35,.35 Bad i/p socket solder joints Laney RB6, 2005 or 2006 Farty noises, reported but not found on arrival or induced. Poor central pin wiper contact inside the "enhance" pot so intermittantly no ground connection. Due to the bent pair of wipers not making good contact with the conductive track. Uses prea ,CA3080 , 5x 072 (SMD)m 2x 680R PA, 2x 10R, 2x 0.22, 2 x SAP16 3 standoff + nuts on the pa board. Beware of misplaced LEDs before refitting. Pull the amp casing rearwards to give enough room to disconnect the speaker connector. Laney VC30 , later than 2004 probably 2007, ser no in 1200s But seemingly not PbF Usual suspects, even though only 2 years old probably. But final straw was mains fuse blowing at switch on, no major problems on previous use. Consumption max 100mA rating plate says and 1.6A antisurge for 115V use and 630mA antisurge for here , 230V use , toroidal transformer. Owner did not chuck the fuse and it is only just blown , ie just a small patch of slight spray of white dust/smoke on the glass at the break so little more than mechanical failure. Assuming nothing else found after taking the amp to bits , replace with 630mA and advise the owner to be prepared to change the fuse every year or so ? , or uprate to 800mA antisurge. Methinking 500mA to 630mA is not enough margin for toroidal and normal switch on surge, no thermistor in schematic or actual, schematic that I have shows 830mA for the 1995 version. Changed to 800mA with note on plate Incidentally the loud thumping noise in these , on movement , is the springlines knocking the cardboard closure and the cardboard acts as a speaker cone. They do not bang against the metal side. Placed a couple of daisy chained large cable ties around the middle so bowing outwards, with some silicone sleeving over as soft then cardboard cover, Coils 215R and 16R. The reverb tank , as usual, is made to be screwed to a cab with soft rubber grommets. I suppose someone decades ago realised that putting them in a cloth bag acoustically decoupled better, hence having to close off the open side with whatever was at hand. Nasty sharp metal guillotined corners need filing back. Mains tr primary 20R Bad exit elbow jack, bent up central tag a bit and a twist of nichrome wire around and under and tightened while the pin is squashed axially , over half cap and tip, in an engineer's cramp. Bad spade connectors on IEC and elsewhere. Poor fuse contacts on 20mm holders, Usual suspect solder points under main board, remove the rocker switches to angle up this board for access. 8R speaker EL84 s despite measuring CH/R of 25 to 35 Meg were giving a noticible amount of flutter/rustle (with all controls ACW) LD Systems DJ200 Wild Thang (sic) WildThang ?, 2007 Just out of warranty - distortion on one channel and crackles. One sense trace (unipolar) excursions only on that channel, expecting blown o/p transistors but all now check out ok. Output undistorted until about 0.8V pk-pk , there was about 0.4V DC on those 5W resistors. They are all buried under the heatsink , so needs taking apart to monitor. Expecting bad solder, RoHS, as solder joints looking like 20 yearold leaded solder joints. No bad solder found - bad layout design. The end of a low power +B wire link ends exactly under a 3.3K 1/4W resistor laying right over it, so touching the bend of the wire. Nothing visibly wrong when received but maybe overheating of a 470R R19 resistor at a TO92 Q7 emitter. Expecting bad solder I started tapping things and phut this insignificant 3.3K , R5 at the collector of a TO92 Q1 burns up. I'm assuming its 3.3K as that was remnant measurement and corresponding channel B is 3.3K. Both these separated resistors are electrically connected in the low power section of the amp and it was the final straw. According to the owner the amp had been overdriven for too long , outdoors, but no sign of that but perhaps enough general heat to flex something. So for these amps bend any resistor away from the ends of any wire links. 2x 470, 4x 4.7R, 8x .25R, NE5532 2SC2073, 2SA940 / 2SA1943, 2SC5200 +/-55V , +/_14.6V 2 x PROT light when protection th sw activated No threadlocking on any pcb screws Fan action questionable, failed tapping test so replaced both pcb plugs and sockets with soldering Fan disconnected , 400Hz , 0.15V in and max vol, gave on one channel nearest fan sw, 5.64V ac over 4R, 23 minutes to raise 34 deg C over ambient, still rising 0.5 deg per min when cancelled test no change in o/p level over test period. With fan reconnected 0.2V, 400Hz in , 1/2 vol and 3.54V over 4R, fan cut in at 33 degree C monitoring with thermometer laying over fins with end and top covers removed. With no I/P , or speaker and 1/2 "vol" On one channel , bank of Rs at fuse end of pcb, approx Vs -57,0,20,0,-20,0 at 0.25Rs ends of other bank -56,0,-55,-55,0,55,0,56 Thermal switches marked VDE KSD 301 2 of this make and type? on power amp heatsink with no other markings other than moulded numbers on the black housing, so unlikely to indicate temp etc. One marked 23 is n/o , to activate fan but seems rather high click over temp (soldering iron activation), temp not actually measured yet. The other is n/c marked 14, overall cutout Anyone know how to decode these mould marks assuming they do relate to temp/type or any other ideas? If I was designing amps ~ I would only use normaly closed switches as failure mode is usually o/c or high impedance plus each of these use 2 pairs of connectors in line back to solder points I would choose fails safe mode. Fan one tested higher than I would have thought but as usually only used at low power , will leave unchanged Fan one cuts in at 68 degree C and out at 45 degree, checked up and down twice for reduced "hysteresis" overall cutout one goes o/c at 90 C and s/c at 60 C Luxtrack Tootsy 2 lighting sequencer No function after being dropped. The mains transformer for the logic is pcb mount type so shock loading had snapped one of the primary wires near the mounting pin.This equipment failed earth-bond safety test. Only the top panel is bonded to mains earth and as it is black anodised (hence insulated)and other panels are not separately bonded so added bonding. Also safety-wise in use the angle Ali heatsink is not firmly held and could flop into touching the chassis. Cover this area of chassis with suitable insulating sheet material. It is too easy just bending the Ali heatsink to get at the drivers area - don't do so, as the pins of the triacs will fracture with age hardening / vibration. Undo each screw mount to remove h/s. For a tighter job remove each triac and push thru pcb pins soldered into place and solder lengths of triac legs to these pins. Mackie CR1604-VLZ 16 channel mixer , 1996 No tape insert inputs and had been used on 240V . Tied the IEC line socket to the mixer IEC chassis plug with a label with large letters saying 120V, The other end of that lead is US plug for the 240V to 120V auto transformer. Unusually, setup for rack mounting so the "back-plate" has upside down and reversed legends.
Back plate has loads of active on it SM 4560 and trannies, the 20 way ribbon probably relates to the tape/in + others. The steel plate is held by 2 torx screws from the inside so you have to remove all the bush-nuts and XLR screws. ps has 2 x 5.6R, 2 x TIP29C, 317 and 337 set for +-15V via 130R. ps outs -15,0,15,-15,0,15,47 and floating 18V on the spade connectors presumably dropping to 12V on load for the lamp. One +-15 for the 4560s and one for the 2601 bar-graph, zener has 48V across it. Replaced the 317 as had overheated. Problem with the 20 way ribbon cable. Once again a piece of expensive kit that does not have shrouded indirect "edge connector" headers so easy to place the socket out of register with the header, especially one line connected to wrong line and one line unconnected. Ribbon leads' red is not a consistent identifier, Red on 40 ways is pin 40,red on 20 and 26 way is pin 1 , where marked on board. pins 18 and 20 of 20 way via 120 ohm to Main Outs 24 ,26 on 26 way via 120R to CR Outs 13,16 on 20 way to main fader top points Middle 40 way +15V on 38,39 +37 40 Way nearest Tape in/outs -15V on 2,4,3 remaining odds tend to be grounds Uses approx 15 off 4560 dual op-amps on rear panel and about 75 on main board plus 2 SIL 4560 for headphone amp and 8 2901 quad comparators for bar graph. The 8 pole 2 way relay marked on the user manual block diagram for SOLO LEDs and signal routing is probably numerous 4560 as gates. Using phones socket outside of chassis needs earth connection. Push RL buttons on each channel to pass feed through to main mixer. To reassemble rear section. Fix the pcb to the steel plate and then connect that to the rear plate. Feed cables through the plate with the long slot and screw through the ali of the ps into the fixing boss on the middle of that plate. Then introduce the 2 parts together and screw the power entry plate to the backplate only at that stage. Machine screws for the Al to Al casing and tapered screws for the XLR sockets. Mackie SRM450, year 2000 Horn output but no bass output. Had intermittently broken output and then one time of powering up, nothing Acces the bass speaker through the front grill not by separating the main body halves. Cutting away the cone the break was at the point where the round form of the voice coil was joined/ deformed to make the flat ribbon to go axial to join up with the braids. Looks like a design flaw the copper wire is pressed to form the axial tails so a stress point there. Also the coarse grill on the magnet end would allow degrading foam particles to pump in and out, really needs a pair of large hemisphere grills one inside the other with fine filter between properly. VC dimensions of the Mackie M1263W 2x 90 turns covering 15mm length, 63.5mm ID of core, thickness with 2x coilwire , 0.9mm Device listings in order power IRFP9140, B817,B940a,C1567 D1264a,D1047,IRFP150N 677F070,B817,B940A,C1567, D1264A,D1047,MJE295,MJE3055T signal c3788,A1478,JE340,JE350 loads of 4560, 1x 4566, LM339M,1x 2068 2x .22, 2x .12, 2x 2.2, 2x20, 2x .22 Mackie SRM450, year 2004 No abuse but failure of horn tweater First problem how to part the 2 main sections of the cab to get to the horn. P/N 0008093 Heated screwdriver as per tips file Drilled out the screw holes a bit for easier assembly/ next disassembly , (will add star washers under heads) Caproic smell came off - what do Americans use as glue or filler for construction plastic ? I only smell it with USA equipment. These Mackie screws, 17 of them, (2 slightly shorter either side of the bass driver) , in my opinion , are bordering on the threshold of shearing without such heating, they deliberately used undersized holes probably. So the second of 2 Mackie SRM450 to have mechanically broken tail at the voice coil. 25 turns of about 0.07 mm silver wire over about 1.75 mm . Previous , different unit the one above in this file, bass driver coil broken where the coil wire is deformed to flat for the tail. Not the slightest trace of overheating on that one. This one, horn , nearly at this tail juncture , the break marked B below, half turn vroken away from the resin core, and again so trace of overheating anywhere. http://home.graffiti.net/diverse:graffiti.net/mackie_horn1.jpg 4 engineering bolts hold the diaphragm to the magnet but it is set in plastic frame, although engineering plastic, presumably can deform enough to catch something. As there is a milled out recess R already there I intend trying to take the + and - tails through the same side, not diametric. Grinding a slot in the aluminium ring to take some 3x3 plaited 46 swg wire as tail. Replacement driver 130 USD , diaphragm 70 USD so worth trying as presumably swap USD for GBP and add some for here. Very little diaphragm movement so should not foul anything. http://home.graffiti.net/diverse:graffiti.net/mackie_horn2.jpg http://home.graffiti.net/diverse:graffiti.net/mackie_horn3.jpg http://home.graffiti.net/diverse:graffiti.net/mackie_horn4.jpg Cone thing presumably just stuck to the metal, fell away on removing the horn part. So it may be an effect of work hardening , relative increase in the effect of imperfections/micro fractures or some other metallurgical effect. Mackie speaker voice coil failures due to this flattening/ribboning process to make the tails to the outside world. Previous failure at the juncture of round to flat (0.07mm round to about 0.02 x 0.2mm) so at the peak stress point. This one along the length of the ribbon section, but the whole 50mm or so run was brittleised and disintegrated on touch, not the slightest sign of overheating on the remaining 25 turns of round wire. broken end marked B on this pic Cannot expore the metallurgy as that curve of "wire" as totally disintegrated to dust. Thought I could solder to remnant and lead in and lead out on the same point, not diametric opposite. But required grinding a slot in the aluminium disc. Doing it in situ with the burr action the wrong way and scudded into the voice coil. Had to replace with an APT horn 85W (6.2R), as much cheaper than Mackie and those are proven suspect anyway. Mounted the APT80 bodged with spacer and washers etc as holes don't line up with Mackie horn section. Added 1 12V, 21W bulb in series as a bit under-rated Threadlock on the horn bolts so heat well before undoing. Bass speaker , yellow leads / horn blue. Tx 5.1R // 0.5,0.5 / 1.0,1.0R 2x 0.22R, 2x 20R, 2x .22 5W 2 x .22 , 2x 2.2K With normal gain set, low cut in and contour out. 17mV input , for 400 Hz, .49V ac over bass and 0.001 V ac over horn for 4 Khz, 17 mV, 0.012 mV over bass and .2V over horn Assuming same power devices and postions as the SRM450 above, not confirmed. for the 4KHz input and voltages left to right along "horn" strip 14.4,0 / -.56,-43, 0 / 0, -43, -.56 dc -1.2,1.2,-.55 / 0,43, .55 / .55 , 43, 0 -15.1,-43,-14.6, 15.2, 42, 14.6 for 400 Hz and "bass" strip dc -42, -88, -42.8 / -.56, 43, 0 -1.2, -42.8, -.55 / -1.2,1.2, -.55 1.2,42, .57 / .57, 42,0 / 41, 87, 42 It may be possible to swap output devices from horn side to bass side and replace the horn ones with lower spec devices, if pushed. Bass amp is Class G, the higher voltages are switched in with the power Fets. Before wrapping up a Mackie SRM450 powered speaker I took some representative DC voltages on the complementary pair power devices of the bass driver amp, for me and all else, future reference. -42, -88, -42.8 41.2, 88, 42 in comparison for horn side amp, same devices 0, -43, -.55 .55 , 43, 0 Probably class G. I don't have the schematic or even saw the track-side of the Mackie board but that explains the presence of power FETs Manacor miniature 8 channel mixer. No output on either output There is no reverse 9V protection so it is easy to change battery with unit on ,touching battery terminals the wrong way and knocking out both LA3210 SIL op-amps so replaced also add 1N4001 in supply line to on-off switch. Marshall AVT50 , 2007 No more than 2 years old and failed springing / closure of input socket and because of leadfree solder all sockets had poor soldering that would have failed in a couple more years and dropper Rs that would have failed sooner than that. Transformer disconnected, 20R// 0.6,0.6R 2x270, .22, 10R 0.5W, 270 7W HT monitor point on R44 nearest C17, 113V +/- 34 "white" supply -4V pin 5 of blue "ribbon" CN4 0,-34V LM317T on o/p board. Thermistor for controlling the 24V fan near but not touching the heatsink. As very quiet fan, bent nearer the heatsink and added white goo . No trace of any goo but slightly puffy silipad under the hybrid o/p so probably overheating as fan (13 V at switch on) was only responding to air/ bourd temperature Marshall AVT 150H, 2002 both tda7293 blown (neg to 0) due to o/p connected to another amp o/p . blown mains fuse mains primary 6R, sec (Yellow) 1.3R, (blue) .8R 2x 2R2, 2x 68R (in circuit), 2x22K .22, 2x 10R, 7805, NJM072, 4056, 2x 4011 one 68R solder joint soon to be iffy +/-49V, +/-24V, +/-15V 24V fans, 145V at D112, ECC83 A1,A2 81V Dummy load test with both fans disconnected and aluminium "heatsink" unbolted from chassis and thermometer laying on top with alongside the TDAs 3mm Al 270x 50mm plus about 270x100 mm under of the rest of the folded sheet. 3V ac into 4R, 400Hz, 20 minutes to reach stability of 45 deg C over ambient and drop to 2.95 V ac Marshall AVT 275 Replacement and befing up of input socket Added filter cloth , glued into top vent, to stop any small biits of wire, staples falling directly into the amp The overdriven / bad bearing noise on the fans is usual for these. Marshall AVT 2000, year 2005 Yanked guitar lead and weakened socket, replaced and beefed up as per tips. Removed the top plastic grill and glued in some pan scourer filter cloth as I don't like being able to see main power devices (staples etc ingress) .22 10W, .22 5W, 2 x 10R, 2x 22K 1W, R209, 211 4.7K 4x 3K3 speakers 6.4R CCOP5, 7915, primary 5.8R, secondaries 2x .3, 2x .5R Marshall 1987X from 2006 and probably other recent models. Traditional chassis mounted pots ie with loose wiring, not loomed, not pcb mount ones. To save cutting small holes in the front fascia, to take the pot ant-rotation lugs, they've cut them off and then not even secured the pots with star washers under the bush nuts or fascia. So even in careful useage the nuts work loose in a couple of years which is fine inside an electric quitar , just a rat's nest of knotted signal wires, no elf 'n safety issue there. But not for valve amps - needs a modification to stop each of the pots rotating and then bare connections touching. The 1mm tinned copper wire earth strap soldered to and across each pot is not enough to stop, wire breaking and the pots rotating. If in an electric guitar I replace the wire with flat copper strip, soldered to each pot case, the sort of enamelled high current wire used in some power transformers, with the enamelling stripped off. In these sorts of cases, not wishing to add to any electrical hazard, 1/8 plastic rod , bridging the back of each pot, and then paired 1/8 inch cable ties around each pot and the rod. Make sure the tie is lodged overe the aluminium fixing points and not the paxolin. These amps have a printed plastic finnish covering over the fascia metal. With a thread lock chemical approach the plastic can still compress under the bush nuts ,microscopically, plus metal creep and soon the pots will turn if the knob is rotated to either endstop. The anti-rotation lugs are there for chassis mount ring tagged and wired pots precisely to stop any chance of rotation - up until the point is reached when the the pot has fallen off , that is. If the wiring was loomed and laced tight it would be a reasonably satisfactory alternative . "Repair" job, that awkward type of one where no fault found. I can understand lager chillers or lighting triacs causing clicks and bangs and noises off but blowing fuses on 2 Marshall valve amps at the same time and no other pub mains problem showing itself. This 1987X kept blowing 500mA HT fuses after the initial failure. Not doing so now its in front of me. Mains fuse always ok , just the HT one repeatedly failing after 4 seconds or so. At the same time as this HT one failed the mains fuse failed on another Marshall connected to the same supply - that one just required a change of mains fuse and is still ok. Could a fault causing failure of HT fuse on one amp cause the failure of mains fuse on another amp , with no pub wiring problem at all, even problem local to the power ring/spur to the stage. Owner didn't notice anything else wrong in the room at the gig and confronting the landlord he said he'd had no problems. Checked the valves and transformers , caps etc and everything seems hunky dory , no wavering of HT of about 440V on dummy load. I looks as though it will have to be replacement 500V, twin 50uF electrolytics although no suspicious heating or bulges /weeping, unless an indisputable reason can be found. Fuses blew to black interior, ie not soft blown. SS diodes in this one. Amp is in pristine condition and owner never goes above 3 . 5 off 500mA (T) fuses blew black before but no problem while here According to Regulation 27 of ESQC Regs 2002, UK mains should be 230V +10% - 6%, which gives a range of 216V to 253V. I variaced up to 250V , switching on and off a few times, giving HT1 of 464 , nicely stable with amp under load. A thorough inspection of all components only revealed slightly loose nuts holding the iron laminations on the filter choke, which I cannot see as a problem. Otherwise inside and out it looks brand new, only some of the large binding post (lead-free of course everywhere ) solder joints looked grey but otherwise sound. On the assumption that the one of the 2x 22nF, 400V DC decouplers to the o/p valves could have failed and self-healed, I replaced those. Marshall 4140 valve amp, 1975 Been in a shed for years and no known history so treading cautiously. Measuring the DC resistance of each side to centre tap of this Marshall amp, shows only about 15 ohm each way for o/p matcher. Amp is 100W o/p using 4 EL34 , two paralleled anodes going to each side of this impedance matcher. Output resistance of about 2.5 and 4.5 for 4 and 8 ohm settings seems fine. I put a 1KHz AC LCR meter on the coils and it comes out to 32 Henries for each half. Amp is 1975 , from electrolytics, and uses Si rectifiers, choke is (in circuit) 105 ohms DC. Charred/burnt 1.5K grid resistors and blown HT fuses. All valves ( all marked Marshall) checked out good on Avo CT160 - I'd forgotten how problematic , with high current valves, to get the initial zero on the meter before rotating the SET mA/V. I always power up kit left idle for a long term with a variac + current meter + thermal trip. Perceived wisdom in such circumstances to power up valve amps with full speaker load on output with all valves in place and to power up transistor amps intitially without load. On the slow variac power up, I usually power up to about 80 per cent mains with no valves in and then add the valves and then go low to 100 percent Replaced the burnt stuff and its back working. Unfortunately after about 10 minutes hum makes an appearance and after half an hour becomes excessive. I stuck a piece of 20 to 35 degree C thermochromic paper to each of the 4 can electrolytics and one is heating up. Its normal for each of the 4 EL34 to have a blue glow observable through some of the holes in the internal metal-work as well as normal orange heater glow. Replaced that dual cap and runs cool and no hum after 10 minutes. But after an hour a hum develops, intrusive but not as bad as before and at the same time a serious glow forms on the zinc coloured metalwork of one pair of the EL34s. All 4 EL34s tested good , otherwise just 2 off 1.5K resistors to the grids of each EL34, correct values cold. The push and the pull from the preamp are AC coupled, replaced all 4 22nF, 400V caps in that area. Not a problem with the DC blocking caps at final push-pull separator stage. Replaced and still hum after 3/4 hour. No DC on the ganged volume pots. Monitoring the negative bias for the output EL34s. 10 minutes in, the -ps voltage at smoothing cap is -52V. The voltage to the (schematic marked) B pair is -39.2V before going to 1.5K then g1 of each EL34 For C pair -39.2V also 25 minutes in B = -37.8, C=-34 45 minutes in B= -36.9 , C=-32.5 hum is getting quite noticable and -ps rail is still -52 Increasing bias pot from its original of 8K to max of 22K brings the -ps down to -53.5 now B=-39 and C=-33 less hum but still going more positive over time and hum increasing. I stopped before the B pair started glowing like before. I was expecting from these voltage readings that it would be the C pair that would start complaining. Switching off the amp, not just to standby, for a couple of minutes , brought things back to original cold situation and another 3/4 hour presumably before hum gets too much. One thing that concerns me is each of these 1.5K g1 resistors has one end to the valve base pin and the other floating in space , not soldered to an insulated pin just the wire connecting through Tip from "Arfa Daily" "However, before rushing out and buying new ones, you can start by removing both the C valves ( these are the ones that glow ultimately - yes ? ), then removing one of the ( likely ) OK B valves and putting it in the C side. The amp will run quite happily with just one valve in each side ( it's a trick that I teach owners to allow them to finish a gig if they have a serious valve failure ). You will then be running it with two valves that have performed OK when they were both in the B side, so if it now works ok, next put them into the two unoccupied sockets instead. If it still continues to work ok, then the chances are that it is a valve problem. If it doesn't, then it must be a bias issue. This assumes of course, that it's nothing to do with the output tranny, which could suffer a partial insulation breakdown, resulting in shorted turns, when it has been running a while. Again, this could be checked by swapping the winding ends betwen anode pairs, and seeing if the bad behaviour swaps sides." Swapped pairs of valves with much less hum noise and better sustained negative bias but assumed a new set of valves would be the answer or having to switch off for a couple of minutes each hour of use. Marshall 6101, 1992 combo, 29Kg Crackles and bangs except at low volume and tinging output with fingernail scraping across the turned metal covers of the knobs.. How to remove the digital board to get to the valve bases hidden under it. The Switchcraft XLR socket is introduced from the outside and soldered to the board with the track side of the board inaccessible. A cunning latch in the XLR socket that releases the internal part that is soldered separatable from the XLR housing. With a jeweller's screwdriver turn the slot at the end of the socket housing to release the latch. No need to undo the 2 mounting screws. Shame about the "dp" pots used as they were weel soldered in , double sided, requiring "soldering" first before desoldering. Poor swage contacts between pot tracks and pins. Removed and squashed in with parallel jaw pliers, treating all vol and gain pots but perhaps should treat all of them. 5.6K 5881 grid resistors were charred but functional as was large 10K on preamp board , replaced with same wattage replacements. As were the 47Rs in the +/-15V ps but replaced with 1W. So problems on all boards. Remove the exposed screw heads to release the boards , hopefully leaving the nylon parts held by the nylock nuts. One ECC83, second from non-transformer end replaced as C/H leakage of 4M, giving tinging. Number 4 was also on way out at 10M. Punched out 5mm diameter bits of cycle inner-tube rubber with a paper punch to pack out the each knob spline recess to raise away from the fascia plate. Speaker 5.4 ohm DC All LEDs lit - release the speaker/line switch No output - use outlet nearest mains inlet. The earth point at the XLR is required for normal function. No ch1 if conn1 lead is disconnected Dummy load test, set for 4 ohm, 2.5V ac 400 Hz cont. sine in load. Ali plate 3.25x7.25 ins resting over 2 large O rings on the 4 6L6 and thermometer on that. Temp stabilised at plus 46 deg C after 25 minutes. Cutting HT then drops to plus 15 deg C, over, on heaters only. Marshall 6101LM, 1998 Smoke billowing out of the line in and out sockets between sound check and use proper, so set in stasndby so low mains current. All fuses fine. But 5A plug fuse replaced with 3A, 2A T in rear chasis housing and 5A Q internal. Line cord replaced as not only burnt hole but melted IEC socket partially and heat transfered to the line cord plug which had part melted also. Flexing of pins from the IEC socket over 10 years of insertion/removal of line cord had broken the solder joints at the pcb, but not the ground pin which is 0.5 inch longer. Maybe compounded by mounting screws being too small a gauge and brass (to match facia). half inch radius burnt hole in the pcb so only the glass matt remained in place. Cut away burnt, cleaned off smoke staining all over chassis panels, and wired in replacement IEC socket so mechanically decoupled from the pcb, but surround re-rivetted to the pcb. Presumably if HT was on at the time and arcing at the bad solder then a fusing action may have occured before heat build up could take place. Also added high temp insulation sheet between transformer and the ps pcb as close. Speaker 6.2R Relays click over at about 60 percent mains Mains Tr 4.7R//14.1R, 0.1R o/p tr 15.8,15.5?? 0.2R,0.1R set to 8 ohm , no speaker If channel change+ LEDs fail to respond , switch off at mains and on White connector -15V,15V, 23V over 10K , R58 313V,445V at pa black wire 227V, 6L6 480V There was also bad solder on a heater wire from one of the fuses, so only mechanically connected. Marshall 8100, 100V, 1994 No reverb, broken coil, 7.2m of 0.07mm wire, 31R and 200R for the other one. o/p coil is grounded only. Decided to slightly bend the brass retaining bracket to release the iron lamina but difficult sliding back in (very soft and thin iron) so drilling out rivets is probably best. Solder the tails to the phono sockets with hotmelt linking the sleeving to the tags for strength. Mains transformer 17.5R, .4R, .4R HT transf 5.6K, 21.5R Output T64,T65 darlingtons are 1.7V & 1.2V diode checks. Marshall AS50R, 2003 Very low level of output TX 33R//.8,.8R speakers 2.7R -31V, 29V supplies to +/-regs +/- 35V power rails With controls mid position 0.1V ac, 400Hz in an aux i/p 0.015V at line out at conn 2 pin 1 .065V and pin 3 .049V Putting 0.01V on pin 9 of the LM3886T gave .44V over 8R Only 5 years old and the Alps 20K lin master vol pot hasd failed, either a build up of something insulating on the resistive wiper or one finger of the conductive wiper moved to inside the track and the other outside. Marshall AVT 50, 2001 drops in volume replaced IC2 072bde with TI 072 R81 , 470R, upped to 0.6W A number of bad solder points, icluding the usual Marshall pillar rather than 1/4 inch spade connectors 120R 7W, 2x270, 0.22,270, 2R2 gain pot had been replaced with A100K then B20k,a1m,b200k a1m,a500k,a1m,a100k b200k,b5k Marshal DSL50 (JCM 2000) 2002 Came in as suspect low channel A throughput as compared to channel B, but this would seem to be normal. Valves tested fine, no switch problems or any other problems found. For equal output the channel B knobs set about half the number setting of channel A. To release valve pcb only, unclip yellow wire,release 6 screws around upper metalwork to release the long pcb standoff screws. R23 270R soldering bad on rear pannel board , supplies the ICs rails with its fellow 270R Marshall JCM 2000, 1998 ? (also see DSL50) Latching switch types ok for VCRs etc, with tight clearances but not here. 2 DPDT worn , leading to problems unless you hold the knob in or out. There is about 2mm of play between the knobs and the holes in the metal of the front/rear panels. Replace those 2 plus 2 more with same 3.5mm pin spacing switches but ALPS make. The 2 off 4PDT switches maybe more resilient to off axis loading so will leave as is , unless anyone knows better. yellow stem "angle with an F" logo, found 4 ALPS marked ones, blue stem replacements and some slightly larger diameter knobs. Required slightly opening out the "gold" fascia holes but not the underlying panel and unfortunately red in colour. Permanent black felt marker over them , cooked in with hot air and repeated again sorted out that aesthetic problem. The easy fudge would be peripheral cut a 5mm LED clip or 8mm with a section removed fitted in the gap , but enlarging the fascia hole a bit, and gluing-in the clips internally. The other problem is the black knobs seem to be pushed on the shafts, hot, rather than gummy glued on , so do not come off easily. To remove knobs squash diagonally in a flat jawed vice. They always seem to split , once, a disguised seam, looks more likely ? Definitely mark all cables and wires before disconnecting from the boards. springline 198R/25R 2x 4.7K,1K, 2x 10K, 2x 4.7K 0.5W, 2x 1K, 3x 270R, 3x 100, 2x 1R rear 100R, 1K mains tx , no valves p 6.5R // purp .1, /blu 1.5,1.5 / o,r 23 o/p R.O .2 / gn bk .4/w 79 pur 40 bk Marshall JTM "1962" from 1993 Working order but for bad pot, but some things are not pukkah. Reconned existing pots The main carying handles, presumably original as no other holes, are just held with woodscrews into thin carcass wood, splintered away internally, as no pilot holes drilled, - replace with nuts/washers and bolts? The screws that hold the main lifting handles have very jagged exposed head-slots as though the windy driver( or bad human) slipped on driving each one, so replace with bolts for that reason alone. Owner is in the habit of going around with switch cleaner for the jack sockets so I will beef up the contact closing force on all those. So did the rubber cord beefing up of all 7x 1/4 inch sockets as described in the tips files. Bad soldering on one wire of the input sockets Finally there is the ridiculous system of casters on these sort of Marshall cabs. It is quite possible for all 4 casters to end up pointing inwards so the slightest of tugs on a guitar lead will pull the cab over. A 9 inch deep cab is then relying on just a 4 inch wide wobbly footprint but still 26 inches high. Especially if used on a carpet. Jacking up the innermost edge of each caster. So the self weight should bias the casters to pointing outwards when at rest , for maximum stability. For normal in line carriage then the change of orientation , via the cant, would have to lift the cab and hopefully that self weight at rest would return the casters to outwards position. To turn inwards would mean itself, unassisted, increasing the height of the cab at that corner so unlikely. The canted casters work well. They are not the original , part recessed ones, presumbly busted off years ago and replaced with standard hardware store ones. Canted casters Propping up on one edge with doubled up rubber feet used for kit, so 4 to each caster. Uncompressed feet stand off height 13mm . Original gap between base of cab and floor of 69mm and still that with feet pointing outwards and 83mm if both pointing inwards. The action to get all 4 feet pointing outwards could not be easier. Run the cab on all 4 casters in the longways sense of the cab , go 4 inches further than required and pull back 4 inches. The transporting action is worse, in the wayward supermarket trolley sense, a mind of its own, so perhaps only one rubber foot per standoff rather than 2 or transport using 2 casters and one of the main lifting handles rather than the top movement handle. Another advantage is the casters then end up an inch or so , each side, further out for an even more secure "wheel base". Uses J174 fet, 2x 160R, 2x 10k, 2x 470R. Parallel 190 ohm speakers , 6R, DC. Dummy load test with 3.25x7.25 ins plate resting directly over the main bottle clamp rings then temp took 35 minutes to go 44 degrees C over ambient with 400 Hz, 4V ac into 8 ohm , dropping 0.5V ac over 35 min. Marshall MF350, Mode Four, 2003 Amp works on its own but no crunch channel via footswitches. Failure of "D" connector pin, fine for intermittant pc use but not repeated making/unmaking. 15 D pinning Bk common, Br OD1,-,R,O,Y,Gn,Bl Vi,Gy,W,-,-,Bk OD2, Bn Rev Hot melt over LED mounts and bare common switch wires near metal switch bodies 4 momentary and 2 latching, and bare joint floating in space. Replaced the solder bucket plug and swathed in hotmelt to stop any pins moving rearwards, and checked the amp one which is pcb mount. Remove top section of rear panel, then top front panel from inside, then 4 screws under and unstick the chassis. Loads of dust in the gap between each pair of heatsinks. Uses 4x tda7293, 3x 0.1R, green (I/C) 100R, 2x 10R, 2x 22K, 2x 2.2R near bridge rec. transformer 2.1R // .9,.9 / .2..2R all I/C 15,-15,5V regs power interconnects to prea 0,1.7,5,4.8,0 .1,.1,5,5,0 to valves -24,-24,15,0,0,-15 , 107V on link6 from stepup D array. Bent inwards the flanges of the interconnect cable D sockets for better screwdown. Marshall MG10CD, 2003 Intermittant cutting out - fuse holder problem Uses TDA2030 , TL072,BA4560 0.1 and 220 large Rs 26V ac , +-16V Marshall MG15CDR, 2004 Volume intermittently going to maximum Due to the bush nut for the input socket falling off any plug pushed in strained the pcb with result that ground side connection to the volume pot failed. Also a plastic cover over the springline suspension plate had fallen off and laying over the springs , needed putting back and held in place with cable ties wrapped around. Uses LM1875T , small w/w is 0.1R Marshall MG30DFX, 2003 Bad effects gain control, maybe spindle grease migrating and off centre wiper action. Bad speaker crimps. 0.1R, 2x 100, 2x150, 33 Marshall MG30DFX, 2004 Intermittently drop in volume. The spring clip had failed at a bend that retained the 7805 to the heatsink shared with the TDA2050. Replaced 7805 just in case. At some point the heatsnk had seriously overheated as the hot formulation hot-melt glue that bound adjascent cap to the board had remelted and spread under the heatsink. speaker 3.6 ohm dc Input switch weak so reinforced with silone cord and Hama. the line out socket has the ground line switched and this was dodgy from grime. With 400Hz in giving 2.5V ac into 4 ohm dummy then heatink gained and settled at plus 46 degrees C in 20 minutes and dropped 0.05V Marshall MG 50 DFX repeated loud bangs on switch on Only about 2 years old, solid state. Series of loud bangs , about 2 a second, for a variable number of seconds but about 10 or 20 seconds calms down to normal. Only at switch on from cold, off and on , minutes or even an hour later , there is no bangs. I originally thought it was due to broken input socket so the input not shorting with no guitar lead connected, was open circuit, meant the input was unterminated. Replaced the socket with a more robust one with functioning switches but because powering up quite soon after initial powering, with me, this symptom did not appear on soak testing. Returned it to owner and of course a few days later and they powering up and bang,bang..... It certainly sounds more like DC surges. Its annoying having to wait so long for electrolytes or whatever to reform, degrade or "plates" deform to be too close. With these amps its possible to disconnect all lines to the output decice and associated comps. After leaving overnight and powering up, this morning, monitoring the line out there was nothing wrong at power up, so preamp opamps probably OK. I Let the DC rails fall to <02V after switching off, Reconnected the output stage and switched on and bang/bang.... Suggests a problem at the output. Replace the small 47uF,63V secondary DC rail electrolytics on this output board and left a few hours before powering up again. I cannot see what chemical ? problem there could be inside the TDA7293 that would take hours to reform. One of those very enigmatic faults. The 3 caps are on main +- rails and the bootstrap facility Changed all 3 caps and now a continuous high level buzz for always , no normal function however long amp is switched off. Put a higher ohmage speaker on output for a bit of leeway. Monitoring the stand-by line there was high amplitude oscillation during the buzzing. Cutting that connection allowing standby control i/p to go low then muted the o/p, as should be. Taking it high via a 3V battery and normal service resumed but whether the original fault is still there plus some feedback low-f oscillating loop involving the stand-by control ? Ther's no oscillation on the downstream side of the cut standby connection. Put 47uF on the standby line and it gradually ramps up to about 6V which is presumably as it should but no oscilllation. Tracing the circuitry back down the standby line and hopefully find a duff cap there. It seems as though there was a very small soot jet on the pcb tracing back to the collector of the little MPSA06 buffering the switch-on hold-off of the standby control. Otherwise cold "diode" checked out ok. Uprated that and associated 6.8V zener and 50V, 220uF cap. Marshall MG 50DFX, 2004, 17Kg Nasty noises due to failure of input switches in 1/4 socket, lost spring action to close. Replaced with a metal barelled socket upside down, wired in. The earthing ring removed , hole punched larger and used on the replacement as a complex grounding scheme. Hot melted into place against the board after placement in the front panel, for anti-rotation reason. Uses TDA7293 with fan, 7815,7915,7805 resistors 10, 0.1, 2x4K7 Marshall MG 50DFX, 2003 Autumnal musty fruity smell Bad buzz, sometimes no output, clicks and bangs and sometimes works properly. Someone must have thrown a pint of cider into the fan vent, inwards blowing fan. Heatsink protected the TDA7293 from being spattered but 6 faults found (so far), dotted around the amp. Washed boards with meths, redid solder points where there was sediment etc Problem on the "ribbons" cleared, put alternating set on the headers and reversed end-to-end the cables. The heatsink is isolated from the chassis but something must have been slightly conducting as -38V (on TDA mounting plate) would go to -28V )38V +rail) when the buzz was present. Placed mica and insulating mount to this tab. C80 loose bad master vol pot, gunge under the wipers Tx 21.5R// 1R,9R 2x 3.3K, 2x 4K7, 220,10 2x 3R2, 2x 470 digital power devices marked 32AB N12A and 27BL N05A pots A20K,a5k, b20k a1m,a20k,c100k,b20k,b100k C type is reverse log so replace with upside down b type , wired in straight rather than crossed. b5k,b5k,b5k,b5k The heatsink is held by cup covered-head screws. Marshall TSL100 reported fault same as switch problem on JCM 2000 reported here Marshall VS65R, 1998 the last time it was used was miked to a house pa as very low level output. By the time I powered it up just some low level crackling whatever vol setting and no signal throughput. More a question of what solder points not o/c. one pin of the bridge rectifier, input 1/4 inch socket signal line, all the large W/W , 1 1W, one axial cap. Beefed up all the solder joints with added "washers" of perforated zinc sheet - If i'd some copper or brass wire mesh I'd have used that. Remade all similar component jpoints. Accutronics sprinline i/p 60R, o/p 220R 10 way connector, p10 = 8V 5 way , p4=-44V,p5 44V preamp rails +/- 15.6V T4 -43.4,-1.1,-44V Marshall "Valvestate" VS65R, 1998 Reported as a nasty farty noise. Yet again an amplifier that does not seem to know that it will spend its working life on top of a large speaker. One tiny drape of hot-melt supposed to stop the main ps caps waggling around - tied them together with a cable tie , separated by a large nylon nut and hot-melted into place and extra around bases. Beefed up the solder points on the caps and W/W Rs with wire and extra solder. Also the pre-amp caps treated similarly. The pcb mount blade connectors will pull out on removing the crimped wires to extact boards. AC transformer supplies 33,0,33 / 300V / 13.6V O/P devices badged Marshall T65 and its compliment T64A (curiously one suffixed A only), Probably T64 = BDV64C, T65 = BDV65C eg Part Number = BDV65C Description = Darlington, Power Darlington T65 NPN silicon darlington power transistor. Complementary epitaxial base transistors in monolithic darlington circuit for audio output stages and general amplifier and switching applications by Magnatec Inc TIP31C, MJF122 (something like an oil film, only under the central spine of the retaining clip that touched this Motorola device, don't know what that means, original oil on sprung clip ?) , 2x R33/5W + R33/7W and 2x 330 on preamp also uses ECC83, 5201A, LM348, TL071, 072BDE Marshall "Valvestate" VS65R, 1998 no reverb and then no audio speaker 6.5R broken wire on one tail of one coil 35R and 205R mains transformer secondaries 13,225,30,0,30 For checking pa , conn1 , pin 6 or 7 .1V signal uses 2x LM348, 74HC4316,,072, 4x 5201A mitsubishi, 4558,2x 180R +/-12V reg, 071 pa 10R, 1W, 1.5K, 5x 0.33R, 4.7R .3W, TIP31C Simulating a guitar pickup. Find a 48 volt coil relay. The one I use is 3.6K and 5.6H. If you've no tuning fork to twang close to it then a set of steel feeler gauges. Ranging from 6 to 10 thou for bass notes to 4 thou pinched close to the tip for high notes. Matrix SR 4000 Guitar tuner Nothing after being dropped. All or most LEDs come on and stay on until switched off. Replaced the 10M crystal. Matrix SR 4000 auto chromatic guitar tuner, 1993? Owner had connected an external 9V ps reversed and knocked out the 78L05 as no reverse protection. Replaced V Reg and cut trace to switch to put a small 150mA diode in line I was intrigued by another 3 pin TO92 device marked 8054 HN 3C31 Presumably working order - just wondered what it did. Probably 8054HN not 8054 datecode , by Seiko, activation voltage 3.8V to 4.2V, battery monitor. One line is connected to INVERSE READ of the 80C51 micro , I didn't trace any other lines. Seems odd having this sophistication to hold the micro from erroneous but not fatal operation but no diode protection against battery or ext ps reversal, especially in a product destined for musos. Mesa Boogie V Twin , 1997 This preamp must have been used in heavy rain, or something like , with the previous owner. Had to drill out one of the casing screws to get inside. Present owner has not had problems for the couple of years in his hands. Vibration of drilling seemed to cure the fault so replaced internals showing water staining Working order , after vibrating , and could not reintroduce the problem, but reported as a mains hum, no output signal , but functioning LEDs. Valves check out on tester fine, no change in any hum swapping them around. No problems on any switches, pots or sockets. Soldering looks fine, No noise on the HT line. Note insulated washer on power inlet socket and beware of bending the red LED on refitting of case. Worn legends are Bypass, Clean, Blues, Solo Gain,Bass, Middle, Treble, Presence Monitoring on phones output some mains buzz at most on minimum of gain pot and least on maximum. No effect on buzz , altering the other pots, was due to having amp out of its case. It transpired owner had used a 12V DC supply when the proper 12V ac unit had cracked at lead outlet. Mesa transformer 1.5R / 250R 12V, 1A. Beefed up with a halved plastic knob glued around, made good wiring, and over a pair cable ties. DC will power the SS and control but 12V ac needed for the internal step up transformer for valves HT Mesa Boogie V twin amp foot pedal , 1998 The bypass and solo LED are just where someone's thumb would go when picking up the unit or a misplaced foot. Ten yearold plastic bexel and glue around LED fails and gets pushed inside. Silver finish brass screw cup/eyelet from ironmongery. Use the wrong way up. With a punch knock the raised bit around the hole, flat. Grind open the hole to take a standard LED bezel. Instead of the ring at rear use a cable tie and glue all together on rear. The cup spreads any thumb / foot loading. The bypass mode only works in normal foot pedal fashion with "to guitar amp" output. Uses 7812, 7812, 7805 2x 4N33, 74HC04, 4x 072, LM386 2x vactrol LED/LDR Step up transformer measures in circuit 28.5 and 4000 ohm With first 12AX7 in place and vacant second socket DC measured to case 243,0,0,14.5,0,243,0,0,0 second in place and first empty 254,248,0,14.4,0,248,0,0,0 With both valves in place and DC at the 4 rectifier diodes 236,95,102V Confusingly, unless not original knobs, they go on 180 degrees from the natural flat positions. Mesa Boogie V twin amp foot pedal , 1998 Bad power inlet socket. Flimsey piece of deformed plastic under the swaged surround of the bush. Interfering with the outer contact which is then gripped by the plastic and no electrical contact after that. Cut away this plastic plus deformed plastic edges of the barrel that are close against this contact so it can move freely. Beefed up by cutting back a piece of small cable tie, recessed over the contact, to pad out a bit and hot-melted onto the pcb. Then 2 small "O" rings over to increase the spring/holding action. Also plastic problems with Mesa , the transformer for UK use, has very week plastic "earth" pin. Mesa Nomad 55 ,1999 Distortion on clean channel and intermittant level drop with external signal in at the "return". Failure in the trace line to one of the o/p valve heaters, making and breaking. Tested the valves , all ok, returned the next day and one of the 12AX7 now snow capped and a neat ring around the top of the glass envelope. Obviously due to the bed-spring gauge of spring inside the can. 2Kg to halve the spring length, probably 2/3 compression in use. No point in replacing without changing all the springs or something. How to reform a weak straight compression spring (easily available) to conical or otherwise fit inside the can and the glass touching end be centrally posistioned. ? Secondly there is no dedent to stop the cans rotating other than use of heavy springs - catch 22. What to do, retrofit, without taking the amp apart to get to the inside of the chassis. So far I've discovered a working , but not elegant solution. One of those brass-eyelet hand pincer/dies pushing the die pin outwards to deform a pip in the aluminium, outwards, 1/4 way round so it locates in one of the 2 chassis cutaways. Needs some rubber padding on the outside so the other anvil half does not excessively damage that local area. Any other solutions anyone else has found, particularly forming or re-forming spring metal to something like conical My attempts are very wonky. This is a work-around for the springs. May have gone too far the other way 200gm rather than 2Kg. Expanded aluminium mesh (for continued ventillation through the central hole in the can) cut to a square to squash inside the can. Straught 12mm diameter compression spring. One end , the last 2mm , bend to point axially. Thread that end through a suitable hole inthe mesh and push around for a near circle and feed back through the mesh with the return poking through the adjascent hole. Curl back the corners of the mesh enough to push into the can. Use a din connector cover to go over the spring and push the mesh into the can. Then with din cover in place , use a screwdriver to push the mesh down to wedge into the can top. The spring then stays centrally and axially located . The eyelet pliers fudge works quite well for dedenting the cans, combined with the existing "O" ring antivibration ring. Uses 56K, 68R, 2x470R 220R, 5W Bad pot marked 593739 0129 , 1M log, probably due to too much grease and migrating onto the pot track. Midiman, M-Audio Omni i/o audio processor for A/D, 2000 Owner plugged in a new microphone that blew one channel. Pre-amp uses a Burr Brown INA103 very low noise instrumentation op-amp. In this M-Audio Omni i/o preamp and an outline design application in the Burr Brown book show much the same circuitry the 48Volt phantom supply to the mike is protected by 6.8K limiter resistors. But to block the 48V DC to the op-amp there is a 10uF/100V electrolytic in each line directly to the inv & non-inv i/p of the op-amp and only 2K to ground. If , as seems in this case, a balanced line microphone with a short to ground is connected to such a system then the +48V / 0V across the elecrolytic will instaneously go to 0V / -48V with -48V directly connected to the op-amp i/p powered from +-15V rails and according to the databook can be taken to only +-12V. Added 2 back to back 6V,1W zeners plus 10R to ground for each of the 2 inputs to each expensive IC. For the blown one replaced with an OP27 very low noise opamp glued over a 16 turned pin socket , with mods, first original pin number and second is OP27 1 to 3 via 68R 7 to 3 via 3K 8 to 4 9 to 7 10 to 6 also on original (turned pin socket) only 6 to 16 10 to 15 via 3K 13 to 14 via 56R Functional replacement for the INA103KP including the -20dB cut. Unit also used NJM4560 SIP amps and a 7555 for 48V generation. J2 DC voltages with all pots set low 1.6,1.6,0,0,0,0,15,0,-15,0,0,0,-13 lines 2 and 3 are the signal lines for the amplified 2 XLR inputs Monaxor MPX 3400E , 2005 ? digital echo mixer Breaking output connector problem A lot of solder points on the rear board were suspect although not seemingli dropped.uses 7805m the spring is for earth connection to front panel Diverse Devices,Southampton,England
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(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.
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