Repair Briefs - Guitar Amplifiers, Band/Stage Gear, F to K

The following are repair briefs for various 
equipment.The infomation is directed
to technically competant repair engineers.Generic terms have 
been used to make this info less model specific,eg terms like 
replace transistor Q123 have not been used.
The equipment is Guitar Amplifiers, Audio Amplifers, Stage Gear.
I would be interested in finding 
any other repair listings on the internet structured as i have 
done ie intended to be less model specific. For convenience using search-engines, 
use keyword divdevrep to target these files.

There is no point in contacting me about any of the following, the 
repair job may have been done 15 years ago .
I cannot clarify or enlarge on any of the following.
In the following V ac means RMS DVM AC volts 
unless stated pk-pk. Mains is 240V, UK

Should the location of this file change please use the keyword "divdev7" in a search engine to find it again

A number of the pictures are now apparently not downloadable, because the hosts have disallowed remote linking although not saying so. To view them , you have to remove the picture file name from the picture URL and put this .htm file name in its place and scroll down to the relevant pic.

Band Amps and other stage gear , A to L

FBT Maxx 2a, powered speaker, 2002 Small lighting unit and this powered speaker shared cheap and nasty plastic multiway mains adaptor. Much crackles and bangs from bad contacts in the adaptor but both survived working order . This amp had smoke coming from it, at the time of the crackling. The bridge rectified 52-0-52V ac supply used to have a cap across it, burnt up to just 2 pins now. Only FBT schema, out there found, is for the MAX 9SA for which that component is 100nF 200V , so replace with disc ceramic of that rating or higher? or C +R ? and of course advice to obtain metal cased mains multiple adaptor. The owner may have interpretted as bad multiway mains connector. This capacitor was .2 inch spacing, same as the one over the bridge for the tweeter amp supplies. That shows no heating at all. That one is mustard yellow 6x2.4x4.2mm high, marked K2R 104K That one must be 100 V rating at least, so probably MLCC for that size, certainly if 200 V rating. The burnt one , same footprint may have been taller or 100V rating only. Probably started with metal migration and MLCC failure , yet again , starting with going ohmic down internal micro-fractures then conflagration eventually, rather than bad adapter leading to multiple mains spikes Replaced with 4 as 2x2 100nF/100V traditional disc ceramic for > 4x power rating and one in place of the K2R one. Unfortunately did not place the discs like to like as far as the leads and voltage punch throgh the coating. Replaced with a 100nF 250V yellow polycarb C. 4 sc + pot nuts 12 large cab sc 10x inch ones hold amp in plus one small to th epcb 8 black sc to remove black metal frame 5K log gain pot replaced, off-axis rotation or bent but bad contact LM3886 for treble sp 4x .22R, 3.9K,47R R,R.Be//Y,Gn,Gn,Bk,Gy,Gy fuses 2x 3.15T IRFP9240 L7815 H/S, + L7915 7x 4560 C1237 protector Tx 90 diam x 58mm Blue primary 144W, 280mH, 10.7R R 52-0-52, 1A, 468mH, 4.4R Gy 23-0-23, .7A, 69mH, 2.3R Gn 20-0-20, .2A, 51mH, 3.6R Both sw out, mid controls, both red LEDs on .1V ? in 400Hz .18V bass, <.001V tweeter 4KHz .003V bass, .046V tweeter 1KHz .156 B, .005 T 10KHz .072 T Ignore the above as the gain setting at half did not match the unaffected powered speaker , it returned and had to adjust, see below. wondering what the tiny non-via vias were , connected by the finest of traces, so minimal current. They must be the "components" marked DS* and DST* all over the power amp page of the Maxx 9 amp , uploaded as Max 9 to Elektrotanya, as some sort of distributed capacitance , inside the board. What is the generic name for this pcb production technique , presumably requiring an intermediary plane but not really multi-layer pcb, and any advantage in design or realibility of amps ? The gain pot on these is reverse log , probably more like reverse log-log, for the 5K pot the half-way split was .28K/5.1K , so a log pot slightly adapted and 2 ends cut and cross-linked wiring. In the end returned the cross wiring to normal and added 330R over the 7K section of the normal 10K log pot I'd placed in there. All controls mid posistion, sw out .1V 400Hz inb .69V over 8R , Tweeter op <1mV .1V 4KHz in B .016V, T .2V FBT max 5a, 2003, not Pbf 18595 gain andvol controls bad knobs R,B,B,BW gain pot 5K log C, Alpha 05C5K centre trace very thin easily broken on desoldering pot support rear of panel undoing sc as the line of pot holes makes the panel weak, so support it. greasy pot tracks dodgey solder at i/p and pots also sp wires from Tx end Bk,Be,R,Bk (main) 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 Acousatronic/Acoustasonic? Junior 1999 Bad fron sockets/solder Leave the stand studs in place on cab , "rotate" the chassis around to clear these bolts. Tank R 56R, W 200R Undo rear panel, cut ribbon B/W cable tie Bk.Gn/Be 5.1R W/Br 5R Tx 15R//1R Fashion a bracket to hold the o/p board to the heatsink Al while working on the main board, to avoid damaging the foil ribbon Bad middle 1/4 in socket marked USA Pat 3536870 and D on moulding Pinning 1 8 7 4 5 9 3 2 6 5 and 8 common 7-8 , 4-5 connected with no inserted jack T is 2, R is 3, 1 gnd Wired in standard tagged sockets Wired the XLR to the pcb and replaced upside down just enough sp lead length to take over front chassis to connect and test. Hum goes by 70 % of mains. Untwist the leads to get a bit more length to assist refitting in cab properly, tank phono use long nose pliers to push home For reverb tank , "white" signal with no ground then loud hum jack in Return or Inst Insert kills amp bad corrossion on tank phonos undo cable ties inside speaker chamber to give more room in the amp section Fender Bassman 250 , PR597, 2005 Bad input socket, is there a generic problem with these? Of course I thought it was a PbF problem but it escaped that , leaded solder inside. Solder joints seem fine and no broken tag. Socket make not seen , not desoldered yet, maybe make underneath. The jack centre line is off-centre of the socket centre line , the sleeve contact is a barrel which is chromed and only makes contact with the now tarnished ground contact if the metal bush nut is tight and the 4 pointed grounding tangs are not bent and are making good contact with chassis metal. So 2 ways of loosing ground contact. With no bush nut the chromed barrel will rotate a few degrees and then just touching contact to the socket ground terminal . Of course I have the preamp out of the chassis now and so do not know what the initial state was other than the bush nut was not loose when received. All compounded by gallons of WD40 squirted everywhere that has certainly lost the tip and ring bypass contacts to ground with no jack inserted. I can see repeated tightening/ overtightening? of the metal bush nut plenty of spanner/wrench force can be applied as metal nut and metal bush) will deform the 4 tangs/ dig deeper pits into the front panel metal, until eventually no contact. An aside , why 2x 10 inch speakers for a bass amp? I expected some no-name Chinese make but no , it is Neutrik with this crappy design. Reassembled preamp with the socket exposed and it was then obvious there is a third way to loose ground contact. There is no sprung contact to the sleeve of the jack , just rests on the chromed barrel , relying on the spring contacts of the tip and ring to supply pressure to keep the sleeve in contact with the inside and innermost small segment of arc of the chromed barrel . Even without WD40 , corrossion and general crud , because of the lever action, it takes very little upward force on the jack, at the cable end , to lift the sleeve and break contact. So failure mechanism probably went like this. Bad ground contact due to slack nut. Instead of tightening, owner squirts WD40 in there which pools in the lower surface of the barrel , collects crud, congeals etc. Eventually he tightens the nut , but by then its too late. The input was always bad from new, according to the owner, but got worse over the years. AFAICS no way could this design be of merchantable quality A get by , on the road, solution to this would probably be some sort of reaming action inside the bush barrel Replaced with 3 sprung contact Cliff with plastic barrel and added star washer wired-in. You can then have something like an interference fit between jack and barrel , so little or no play in any off-axis direction. Because the Neutrik is metal and metal there has to be a clearance fit and so its easy to break the sleeve contact. Neutrik barrel internal about 6.30mm, 6.20 jack sleeve, Cliff So 6.68mm The other unprofessional thing , strips of sticky tape on the pot shafts to keep the knobs on About 1/8 th turn on average to tighten all op sc Another problem in waiting. One of the o/p TOP3 the thread on the alumininium "heatsink" block was stripped , presumably at production, not loose but could not take any normal tightening force. Had to fashion up a spring clip instead of the thru bolt, grinding a hole in the spring steel to take one of the large hs bolts upside down. Knobs held on by gummy tape. PREA 6x BA5460, 8x 072, CA3080E PA similar to Bassman 200 PA 4xC3263, 4X A1294,C4793,A1837,7815,7915 8x .15R, 2x 47R 2W,2x 3K3 1W, 10R .5W inrush thermistor 3.4R cold Tx 6R// Be-Be 1.1R, 17-0-17V .24A/ R-R .4R, 40-0-40V 6.3A (cutout 141 deg C) Return So T&R has bypass sw in circuit 0.1V 400Hz in , all pots 1/2 and sw out 5.3V over 8R TOP3 .56V, 57,0 -.56, -57,0 TO220 1.2V,57,.57 -1.2,-57, -.57 sp independent of rear pot 2.7R Fender Blues de luxe , PR246, Jason Sansome mod 2007 mod was stripping out the solid state section and replacing with one more valve for reverb amp and tagged hard wired board . Excessive hum etc now .7mV DVM hum noise over speaker vol 1 , no input , to about 100mV on mid vol. 17 to 500mV with no input plug in place. Celestion G12 vintage 30, 8R, 7.4R dc Mains Tx pink white cut off .5R pu/pu ,2R, r/r 127R, prim 9.5R Instead of the original 3x 12AX7 it now has 2 and 2x 12AT7 and a 5AR4 rectifier and 6L6GC Winged C, SED o/p tx NSC018343 rev B, 288-9608 choke D-022707 , .93H EIA 606-508 Replacement Mains tx VYLX ? 004A wh& pk 220 &230V 350 R, 50V Y, CT Bk, 350V R, .14A / or 6.3V, 4A / 5V 3A vi I think I've found the distortion problem, duff 12AX7 socket pin. Remaining problems are both large Tx only held to the chassis by wishful thinking. And excess hum (for this owner), bad replacement pots (tagged, not the original pcb ones). The output matcher had to be moved to accommodate a different speaker, and not well mounted . Badly blanked off front panel holes for niow deleted functions. Other than the cab little seems original, o/p Tx, choke, knobs, chassis , valve bases and the jewel pilot lamp holder is about the sum of it Luckily surplus Rexine in the amp cavity to salvage for where their pet rabbit has eaten the exposed covering. like the AB868 with the vibrato ch removed Another thing that has remained from the original. That manurey/goaty / caproic acid smell that emerges when Fender (and other USA-made) amps are opened to the air in the UK. No one else has come up with another explanation - so I will stay with the US-patented use of fatty acids from abattoir sources as a part of the formulation of the insulation of transformer magnet wire. Then some reaction to UK humidity or UK-specific microbial action. Not an unpleasant smell , just agricultural, not what you expect to come from electronic kit. This amp has a UK made mains transformer replacement so the smell , if from inside the transformers then from the choke or the output Tx . I deliberately kept the cab in another room this time , no smell there, so not horse glue used in the cab making. recverb tx in cct 61R, 1140R (no markings) tank 190R, 25.7R bad vol pot, not original pots round off sharp corners of chassis metal drive and presence pots not connected Used black collet knob covers and snap rivets to mask holes left in the front panel and unsightly bolts in the holes as blank offs. reverb section like Bandmaster AA768 , Tr side of tank supplied by doubled up 12AT7 V3with 2K2 changed to 680R Rx side to 1/2 AX7 of V2 choke 150R o/p tx 35.6R/50.8R 50Hz 2V pk-pk over 8R , mains hum with no chassis grounding With no grounfd and 600R Sig gen source ok but 36K mic source then 50Hz oscillation. Added 2 x 120uF in series over HT1 for reduced hum Fender Blues Junior III , 2010, PbF Loss of reverb Remove the 3 easy sc , then turn the tank to remove the one under the sp. Remove the brass inserts to avoid them dropping out Coils 55/202R, bad 2 pin connection probably tinpest on the connector face. Removed both connectora and hard wired in adding hotmelt to mitigate flexing of the wires and breaking of solder joints. Inspected all pcb as PbF and redid the usual suspects. Pull out the LED clip from the bezel, remove gland for tank leads, remove rear sp board , remove valve board and cut cable ties to give enough room for to remove the main pcb. Beware of loosing ferrules on the pot shafts 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 Champion "600" PR722 , 2008, marked with RoHS tick symbol A technical issue - if anyone is up on the matter as twice in one month . PbF solder being used on boards apparently made from substrate not specified for PbF , or rather the extra temperatures/heat reached in the soldering process. From the E number and type number these amp boards are for PbF use but the board material is rated 260 deg C/ 8second dwell (270 /10 for PbF , 260/10 for SnPb and 288/8 for polyimide high temp material ) so lower spec than the already lower spec (8 second dwell time) of traditional solder formulation boards. 1W 1K. 2x470, 2x100 .5W, 2x 100K Too much mains hum C6 22uF/450V, added 2x 220uF/385V (as have a heap) in series , with 160K over each. Noise measured by DVM ac over 3.4R of speaker read as 8mV with no input and no vol After extra smoothing measured less than 1mV , vol 1 to 12 Heatshrink cover and cable tied into avilable space and wired to 2 diodes, for C6, as solder points <1mV vol 1 to 12 with no input Fender Concert 1982/86? Bad rustle noise even with no input, ie shorted i/p Clamp rear chassis flange to cab top, remove 4 top long screws, Upend cab and undo 3 rear woodscrews and lift out chassis. Worn screw holes, fill each with hot melt gun held firmly on hole and stick pushed in firmly to inject melt. Before cooling add a pop-rivet to each as pilot hole. Valve 3 tested poor gain at 1.1 and 1.4 Valves 2 and 5 microphonic if tapped but otherwise ok Reverb Tr 1920//.8R op match tr 2845R red/blue, 2695 red/or mains tr 4.6R//.1R green, 16.3R red, 2.8R brn 10V ESR on covered caps starting from 220uF, .2,.2,1.1,1.3,1.2,.5,.5R Without screening covers on noticeable 100Hz mains triac spike noise Speaker Jensen NEO 12/100 measured 6.9R Bad splitter-driver plate/anode 100K resistor, what goes bad with them? Causing rustle noise in output. Partial crack? or something chemical. I may as well replace the 82K while I'm at it and replacing all makes sense. Problem at other end with grounding of a solder point , probably due to previous repairer not introducing phenolic or ptfe board between the boards before desoldering or soldering in a component (puncture hole), added a piece of board. Anyone happen to know the datecode structure for Mallory electrolytics of the 1980s? say 4uF, 450VDC marked 012022 235 8346B 1982 and 35/52 from 235 or 1983 and 46/52 from the last number? Sometimes still noisy at power up , sometimes not. Had it running out of the cab with the noise. Removed V1 to V6 leaving just 3 valves and still noise. Pushing twizzle into the empty sockets influenced the noise. Did not think of the diverter switches but due to corrossion or something on the o/p diverter sw. Confirm the c/o perated after this mod. Cleaned contact area and opened the contacts by inserting jack. Then smallest of neoprene O rings expanded on Hellerman pliers and laid over. Then with lacing cord in tortuous path to hold this ring up near the widest gap of the contacts. Required going part round the bush , seated so not interfering with back nus etc 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 A second Fender in one week with these dodgey input sockets. This time a FM65R , 2006. Although PbF I don't think it was that although I don't like the way the solder blobs don't seem to sweat/adhere to the pads properly. Off centre shallow format , this time no make/model mark just an R on an inside surface but almost identical to the previous Climb 8, the metal forming is a bit different with U contact form rather than more V shape. Perhaps they don't like Brit air, nasty black CuS? tarnish to all surfaces not enclosed by the plastic, those surfaces are bright. Combined with the cross-coupling between the 2 inputs allows more chance of contacts failure. Will have to change those 2 plus the other 2 using the bypass contacts leave side sc i ncab as holds front pilot , undo black barrel and pull out Bl p105 & p109 wiring R p5 p3 y p4 Bend back side hank-bush mounts before refitting to chassis Fender Hot Rod, 2004, PR246 Inability for channels or drive to remain set , via footswitch Reverse action sash cramp to remove and reinsert amp into cab. Both fs LEDs off but feint red on the front panel and bad mains buzz on the op. Bad ribbon or soldering or valve to V2 area Bad aux sp socket bypass contact. Inch long piece of multistrand randomly wire stuck to C40 Pilot lamp marked C47 China replacesd with 7V bayonet Touching the second ribbon to V2 would set off these ptoblems. Ring cracks of solder to p1, p2 , p3 of V2 valve base, remade and all such joints on that board, wrong size pcb holes for the pin diameters on the bases. Clean the sp sw contacts and Small nylon cable tie through the tip contacts bunch and around / through the wiring to the other pins and draw tight enough to retain a circular form and add pressure to the colosing contact but not so tight its not possible to plug into or extract a plug. Fs 0050419000 remove sc on face with 1/4 in so, and slide out. Redid all sw and so solder joints Fender Hot Rod, 2004, PR246 loss of reverb and ch select, no relay click loose 470R, 5W in ps, Mounted both off the board with pins and tied both together with silicone sleeving increased solder lengths over zener traces loose pa pcb screws Serious loss of output and distortion but mains current draw increases with input signal. Bad contacts on sp sockets o/p Tx 112.87R to red wire with all pots at 1/2 10mV in , 53mV over 8R only but 94mV at preamp out Triggering isiolated sw of mains side of amp in socket leads to oscillation? and increasing mains draw 399V and 394V over 470R of both 6L6 -50.6 and -41.6 on bias pot .107 V into PA and only .066V over 8R at o/p Top contact of this socket broken , but not used as ring contact for stereo domestic amps For tracing purposes Ribbon to V3 splitter valve from black wire W2 to wiper of Reverb pot, w3 to common isolated sw nearest mains end of amp, N/C to R28 and N/O to R41, Tip contact to C19 and N/C of other isolated sw , N/O and comon to Gnd O/P Tx secondaries 0.2R Bk + Gn/Y, .5R Bk+Gn Speaker jack plug put in Ext Socket and plain unconnected dummy plug put in normal 8R socket and full level at the speaker jack, wheras sp jack in normal and insulation between sw contacts same bad output Complex socket, clean th eN/C contacts and normal single contact bend the contact radially outwards while pressing on th eTip contact. If fails to short the Tx o/p , if no plugs inserted, then just the same as most other valve amps Fender Hot Rod PR 246 probably 2005 from IC datecodes , "Made in Mexico" . Something in excess of 20 bad solder joints. Indentation and 'cool' soldering iron tests and lack of crystalline haze with admixture of leaded solder indicates it is leaded solder. But appearance is more conical than spherical. Known bad supply of conventional solder there and then , contaminated , eg greasy, component leads ? Mesh screening over the tank cables in danger of touching stuff. Covered with insulation tape and then black nylon spiral wrap to keep in place. Owner thought the intermittant problems were bad pots and tried pulling the knobs off rather than removing grubs and destroyed all the pots. To make the Brightness 22K C-law reverse log pot as cannot fudge with external pairs of resistors as variable R , not pot function. Start with linear 47K , remove rear can, and last half of track lay down some nickel RFI paint outside existing track thinning to the mid of track. If R too low cut knotches into the nickel. Laquer over when satisfied. cut back section of rear can that would touch this added track and cover the retaining lugs in that section with kapatan tape insulation before replacing. Fender Hot Rod de Luxe PR 246 probably 2005 from IC datecodes , "Made in Mexico" Very worn "letraset" type printing on panels. Output jumping between 2 levels. .5mV in , 400Hz, , yellow ch, 1.4V over the speaker No LED ch, .23V ac, all mid controls Mains Tx wiring for 240V, viewed from back to front P15 Bn Bn, W, Bk.Bk Bk Pu P11 P. P12 R P4 W+Bk, W , P8 Bk?+Y / P,Bk Touching main board side of ribbon PW3A caused disturbance of output. Bad solder associated with R78 and its neighbour, diodes and soon to be bad input sockets. Redid all usual suspects and ends of ribbons , bending cable while molten solder to check the wires moved in the melt, in case of broken wires. Removed the 5W droppers and elevated them off the board with trident pins and tied together with silicone sleeving passing through the central gap for air movement. Fender HRD Reported fault/cure 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 , PR772, 2009, Mexico Like the previous time quoted below, thought it was a PbF problem at the input socket, as a definite problem in that area causing about 1/10th volume but not mains noise intrusion, when testing on receipt PbF solder used inside but nowhere stated , as per usual. The same symptoms appeared before and as used with a footpedal at that point, under warranty Fender replaced the foot pedal. Is the schematic for this digital+valve amp around ? I cannot see how loss of ground contact and ring contact to ground would cause a consistent (in failure) 1/10 or so volume drop. PbF solder points at the socket (now managed to remove the preA pcb ) look good (for PbF) No WD40 this time, input socket bush nut , not loose on receipt, same off centre type , not desoldered yet but probably another junk Neutrik. The 2 parts of the barrel turn relative to one another ,easily , without the bush nut in place braced against the chassis previous experience " Fender Bassman 250 , PR597, 2005 Bad input socket, is there a generic problem with these? Of course I thought it was a PbF problem but it escaped that , leaded solder inside. Solder joints seem fine and no broken tag. Socket make not seen , not desoldered yet, maybe make underneath. The jack centre line is off-centre of the socket centre line , the sleeve contact is a barrel which is chromed and only makes contact with the now tarnished ground contact if the metal bush nut is tight and the 4 pointed grounding tangs are not bent and are making good contact with chassis metal. So 2 ways of loosing ground contact. With no bush nut the chromed barrel will rotate a few degrees and then just touching contact to the socket ground terminal . Of course I have the preamp out of the chassis now and so do not know what the initial state was other than the bush nut was not loose when received. All compounded by gallons of WD40 squirted everywhere that has certainly lost the tip and ring bypass contacts to ground with no jack inserted. I can see repeated tightening/ overtightening? of the metal bush nut plenty of spanner/wrench force can be applied as metal nut and metal bush) will deform the 4 tangs/ dig deeper pits into the front panel metal, until eventually no contact. I expected some no-name Chinese make but no , it is Neutrik with this crappy design. PRE Reassembled preamp with the socket exposed and it was then obvious there is a third way to loose ground contact. There is no sprung contact to the sleeve of the jack , just rests on the chromed barrel , relying on the spring contacts of the tip and ring to supply pressure to keep the sleeve in contact with the inside and innermost small segment of arc of the chromed barrel . Even without WD40 , corrossion and general crud , because of the lever action, it takes very little upward force on the jack, at the cable end , to lift the sleeve and break contact. So failure mechanism probably went like this. Bad ground contact due to slack nut. Instead of tightening, owner squirts WD40 in there which pools in the lower surface of the barrel , collects crud, congeals etc. Eventually he tightens the nut , but by then its too late. The input was always bad from new, according to the owner, but got worse over the years. AFAICS no way could this design be of merchantable quality A get by , on the road, solution to this would probably be some sort of reaming action inside the bush barrel Replaced with 3 sprung contact Cliff with plastic barrel and added star washer wired-in. You can then have something like an interference fit between jack and barrel , so little or no play in any off-axis direction. Because the Neutrik is metal and metal there has to be a clearance fit and so its easy to break the sleeve contact. Neutrik barrel internal about 6.30mm, 6.20 jack sleeve, Cliff So 6.68mm " Very little force holding the preA interconnects in place. With a wood block push in the LEDs from the front D28 is top LED cut cable ties number the ribbons unscrew internal barrel of pilot lamp to remove slide PREA to mains Tx end to a position where the headers won't foul. While bending the Tx wires at the pcb edge, force the pot shafts ove rthe chassis edge. Replace WJ9 and WJ10 with terminals for soldering/desoldering next time Mains NTC ,10D-15, 11R cold Check you have not bent the open frame test header of the digital board Mains Tx canted over from being dropped in original shipping 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 turns of 45 SWG. NB safer to leave the rear metal guard attached to the back cab cover and so avoid putting long bolts in there instead of the 2 short ones. Check the +/-15V supplies to U2 and solder arond the 5 W droppers if reverb drops out. For checking the 56R / 215R or so of the tank at U2 use the screens not chassis ground as 1 ground to tank only Seems to have cured the problem again, just wish I knew exactly how and why. Will have to wait until a PR772 circuit emerges out there, the input line goes off simply to a TL072 but there is compexity around the ground lines and chassis KISS, replaced the "Dyson" over-designed Neutrik with a plain and simple Cliff .25 inch socket of which the design and materials have been around for 40 years or so. The previous Fender Bassman never bounced back so this cure must have worked on that occassion. No one else come across problems with these Neutrik sockets? There is a ground/ quasi-ground?/switching? line that goes off via a ribbon to the PA somewhere, removing the PreA board was enough to be getting on with , without added intellectual exercise removing the PA board just to see where that line went The only mechanism I can see for this 1/10 volume throughput. The Neutrik design flaw inside the ground/barrel section, whereby tight bush nut but the 4 sharp tangs have produced pits that then get aluminium oxide coatings from the chassis metal or tinpest build up at the loose part inside the barrel section. Say it builds up to 5K ohm resistance , then loss of ring contact and so instead of say 500 ohm of a pickup it is now 5K5 presented to the input of the amp and attenuated signal current 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 Frontman 212R amp, 2010 Yes, just out of warranty, even if in warranty little point in an exchange because the same would likely occur a year after that. Of course yet again recent made in China for USA and then export to here UK, so absolutely no mention of RoHs / PbF anywhere - anyone the definitive answer? Low level domestic use and failed to no output , no hiss or anything, during usual low volume use. Both // speakers are o/c. One must have quietly failed unnoticed and then the second , I don't expect to see burnt coils if I explore that far . Will of course check for o/p DC or ultrasonic but no reported magic smoke/smells or noise or signs of excess heat. The killer ;-( is the mains transformer is only hanging in there on a wing and a prayer - 3 of the 4 retaining nuts dropped off, fourth totally loose and primary tail mains-wire rubbing on the abrasive ceramic edge of a 5W W/W Only looked into one speaker so far, probably glue failure, then stressing the wire. Break where the axial line of the VC wire bends to the cone angle, not at joins to the pigtails. Fixable without going into the internal space then reconing, just the dome space. No VC former discolouration , VC measures 6.1R for 8R speaker Don't know what the markings mean , assumed cone of 1-20-09 was USA year date, sticker on basket had G5009062257 Q1 But the other on cone is 3-13-096 and G5009062253 Q1 ,so unlikely the same batch. Doubt he drove it enough to knock out the second one by overdriving, getting the same level as before Exact same problem inside other speaker, the change of angle at the cone and cylinder glue line, the other lead this time, again no overheating of VC. Have to assume this is a generic failing with all these Fender badged G.... 12 inchers (only 2Kg each seem rather light) . Will bridge all 4 of these failure points with multistrabd stripped down hook-up wire through a needle hole in the cone. Definitely PbF solder on the speakers perhaps coded in those G numbers no explicit reference to this. Another failing on this Fender. Uses intermediary Al block between immediate o/p h/s plate and chassis. White goo on both surfaces is still as placed, not splurged out. Failure to fettle/de-burr the post machining raised rims around the machined holes so acting as thin washers so heat just going through the 3 bolts not body of Al. The sort of conformal coating final process at the pcb production phase is a staining coat ,soldermask? , usually green these days. White rings showing around the solder pads after soldering may show elevated soldering temperature has been used or wrong composite material body , showing rings of plain white polyester+fibre board . The green staining having melded into the plastic or evaporated. From 6 digit E number E254931 and board type KY-1 this is designated 260 deg C / 10 second solder dwell ( for conventional soldering) rather than 270 deg / 10 second dwell of proper made for PbF pcb boards. This amp has mo mention of PbF anywhere. Fender Accutronics Red 54R/ white 152R C3263 , A1294, C3298, A1306A 6x BA4560, 2x TL072 5W 2x 330R, 4x R22, 1K2, 4K7, 22R, 2x 15K 4K7, 470, 1K2, 2K2 Mains 26R via NTC , 10D-15 , 15.8R cold Tx 9R5// .6-0-.6R, 4mm bolts , nuts loose holding laminations together . Replaced with 4 x 4mm plain nuts , starwashers and bolt ends graunched with double action double edge cutters. Leave mains LED in place , stagger cutting the leads , to remove main pcb All pots at 1/2, 400Hz, no reverb tank,clean ch, 9mV in 1.04V over 8R dummy load o/p DC .7,40,.1 / 1.3, 40,.7 / -1.3, 40,-.7 / -.7, -40, -.1 17V on R144 and -17V on R145 Fender Hot Rod , PR246 ,2006 Distortion on clean ch like distortion pedal on high gain. 13V ac , 400Hz over 8R and clipping with sig gen into PA-In so Tank 58R red at amp , 98K white at amp Base/ribbon problem? V2 solder problem? Fender Junior , broken reverb. Velcro'd front panel, remove and then one speaker to get to tank 208R coil scraped back the exposed tails . Tested for continuity, soldered a fine wire to the eraant one and bridged the break, added hot melt over the fudge and also the wires at the connectors 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 hotrod de luxe no pilot lamp blown yellow LED only , more or less yellow on pressing normal/bright but no no reverb at all, touching signal wires from tank and no induced hum +16V on one 5W dropper but -53V not -16V on the other Fender hot rod no channel switching and over-drive distortion on the clean ch D28 switches over ok .5/9.5V R84 -9 to -9.8 either ch TP31, -9.8V bad solder on +ve rail dropper for opamp supply. Make sure pillared replacemet, to hold Rs off the pcb have flanges on both sides of the pcb, so cannot drop back through under vibration 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 (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 horse 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. Fender PRO 185, Black terminal to reverb bad due to corrossion at the tank grounding point leading to bad crackle in amp even if all controls at min. for 240V red to CP11, CP10+cp12, Y CP7, CP5- , R, Bk Bk+W stripe, Bk+Y, CP9-, speaker black to outside of pcb reverb R BT1, Bk BT3 R 54R , Bk 191R red gns is isolated black , small screw and nut with solder tag through hollow brass rivet and soldered to wire. To protect the ribbon between main and small pcb tie the 2 together while working on . R175 and 176 scrape back traces to increase solder , resolder all large lumps, includinng L1, and zeners and tighted all TO3 and TO220 bolts Fender Rumble 100 bass combo, 2006, Ser no IA06 ... S/S o/p not valve, Fender and RoHS policy ? Up to now if anyone asked me for advice on buying long-term reliable amps etc I'd say avoid anything with a green sticker on the back saying RoHS. Up to now I've also said its probably ok to buy recent USA equipment. But it looks as though I'll have to change that to "if it says made in the USA on the back". Or would that be false advice. ? This Fender fell over onto concrete and got a stove in front panel. But issue for this thread is there is no statement on the back saying anything about RoHS or PbF but pa and prea boards have RoHS printed on the overlay and obviously nasty soldering and "Made in Indonesia" on the back . Is there post-2006 equipment marked "Made in USA" but hides RoHS boards and components inside? It says "A product of Fender ...... " Export model, 230 V mains only at the IEC mains Tx 13R// 1.2R r-r 2x C3263, 2x A1294 2x C4793, A1837 LM13700M dual transconductance op amps with SM to DIL converter 4x 0.15R, 2x470, 2x 47R,2W, 750 TL072 on pa prea 47, 2x 270, BA4560,4x TL072 5x 10K/B pots and 50K /B +/-16.3 dc supplies speaker 3.5R and piezo Beware the pots are mounted upside down here for knob index marks. Remove handle, top 4 sc, and 2 side ones Access , undo 4 speaker leads then cut 2 cable ties to disconnect the red lamp supply wires Replaced the input socket with a proper wired in one the original domestic amp headphone socket marked CHS A and pin numbers 6239 and 5478 4 is ring, 7 is tip, unmarked 1 is gnd 6 is common to pins 2 and 5 // 9 is common to pins 3 and 8 of isolated sw 6-2 and 3-9 with plug out No load "top line " o/p Tr voltages .5,45,0//1.2,45,.6//,5,45,0 -.5,1,2,-1.2//-.6,-45,0 -1.1,-45,-.5/-.5,-45,0 Load test with all pots at mid position 4R load , 400Hz, 0.2V ac i/p and L shaped heatsink removed from casing, and thermometer along the top of the Al 10 minutes rose 44 deg C over ambient and 4.63V dropping to 4.49V over 4R. I dropped input to .15V ac as now nearing 70 deg C and then further 6 minutes to settle to 55 deg C over ambient Fender Showman from 1963 microphony from V1 with one side down to gain of 1.1 AA4263 on chassis 606307 datecode on choke, 606337 on mains , 606309 on op op tr 32.3R, 26.0R mains for 240V 8.6R// Gn-Gn <>.1R with bulb, R-R 70, R-R+B 28.5R Known history with this , from its purchase in Germany onwards, including its original set of valves (not in there and used now, but will test out of curiosity). What are the main potential safety/reliability issues with an amp of this age? All the cotton covered wiring looks good but is there some test/procedure more convincing as to insualting value? Bakelite brittleness in the valve bases? metallurgical failure of springiness of valve contacts? Someone modified to 3 core mains cable and made an earth point, for 240V land, at some point in its history. Numerous caps replaced in 1991 and 1997 and some carbon R replaced with MO at some point not anchored to NP pin6s so rewired the 470 G2 resistors back to p6 tags. pilot lamp 6V, 3W, 1.1R unscrewed Cap Minimite 20uF, 525V date coded 6339 ESR of main caps 1.54, 1.26 20uF .27,.25 60/350 .55, 1.08 50+50/500V .1V 400Hz in 3.1V over 8R normal and bright all mid position controls Tremolo active with sw from rear closed Fender SPL 9000 , 1997 slave amp Ch B volume at half that of A About half the solder joints on the input sub-board are bad. A .25 and M&F XLR each ch with no obvious reason why, as all sockets are individually fixed to stout chassis metal . Even the never been used quarter inch sockets have bad solder joints. The solder looks good otherwise. Probably the sockets were soldered onto the pcb without laying on a jig. So misaligned when fixed onto chassis. So inbuilt stress in board combined with the board being in the internal hot air flow to the fan unbalanced "reference planes". insulated 1/4 in i/p sockets . Lipped insulator washer and star washer inside chassis but only the insulator washer packing lines up with XLR rear faces, just that 1/10 inch or less enough to stress the board/solder leave 4 screws in top plate .46V diode DVM with grounfd lift /11V 400Hz, in and 270R load then 3.3V over o.p with mid vol 2x 8R load, 1.24V out with .184V in each ch ch B XLR so to Pl no continuity , mid pin Remove all bottom panel screws 4x MJ15022, 4x 15023 C2336, C1567, A1008, 8x .22R, 2x 4R, 2x 10R 3W prea R116 6K2 4K3, 3x 20K, 2x 3K9 MAC15 BA4558 94R in cct fan board , poor solder Fast 8A 20mm fuse undo screw at fuse end and unclip 4 standoffs F2 M in circle 61 on h/s 2 wire therm 136R cold C2238B, A968B Beware of little support of main board with base removed so hold main h/s when tightening all TO3 & TO220 no 8R load TO3 .44V DVM diode test to gnd C-E test of TO220 .43V one way ea .53/.58 pin 2/3test TO126 .63/>1.4V prea TO220 1/2 mains +/-37V -1.2,-37.6,-.5 TO220 -1.2,1.3,-.5 TO126 1.3,37.6, .6 +/- 1.3 on prea TO220 to h/s Mains Tx saturating? above 80 percent mains . draw .7 amp at full mains +/-77V on TO3 cold 57V ac across fan raising mains to 100 percent signal throuput drops out, unbalanced DC rail protection acting? no o/p relays Fender Stage 100, 2003 White goo peril? more magnetising current draw from mains than I like to see, rated 230V I don't think anyone else had been in there before me, so a QC issue perhaps. I would not have thought the same person would be soldering components to the boards as well as assembly. Perhaps in-factory re-work stage leads to this sort of contamination, but still QC issue. Looked like PbF solder in a number of places but I think it was white heatsink compound incorporated into some of the solder joints. Most noticably one of the speaker wires loose, as the solder had not adhered to the pad in the most part and just touching contact when it wanted to. Then of course handfulls of white goo where there is AFAIK no point , between and all over the Al spacer bar , chasis and heatsink plate itself, as distinct from just a necessary mustard seed size lump under each TOP66 where the heat transfer concentration is. One Tx wire crimp was just laying in place due to the curvature of the wire , applying some force, and touching contact sometimes. A number of the others were inadequte clamping force to the posts Is there a problem with "Climb 8" make of 0.25 inch sockets as there was also a problem with that input socket but solder and springiness seemed good, seem very floppy in not enough plastic for the housing allowing the jack to move all over the place. Wired in upside down replacement will go in there. For good measure the only hardware that was tight was the backnut for the pilot LED holder. All TOP66 bolts, heatsink bolts, pot and rotary sw bush nuts ,1/4 in socket nuts, spade connectors and the mains Tx holding nuts all needed tightening . Added graunched on 3mm nuts to the bolts and drilled out the Al bar spacer to take them Fender Stage 1000, 2005 or so With 240V mains and no load the mains Tx is saturating with , not too intrusive laminations buzz, with a current draw of .34 amps , normal? Tx seems adequate size for this combo In for "stuck" tuner display. One LED solder bridge from manufacture, cannot ever have displayed, must have eventually draggged down 74HCT595 and now all LED are on for flat/sharp section, other section , main scale note DISPLAY , and its 595 working . just about to order some ( minimum order constraints) 74HCT595 and I noticed it is actually 74AHCT595 perhaps I will try a repinned 74HC4094 that I have laying around I'm more concerned about the 1/3 amp of current of saturation , checked with the secondaries disconnected. Such equipment would have been condemned where I used to work, but I assume anything goes these days, made for UK with 230V on the rating plate. Does this sort of thing come into CE compliance? backhanders from the utility companies to increase consumption ? I confirmed the SD-IN is valid , lashing up a 4015 and will probably get some HCT595 as there seems just one seriously over-priced supplier in the uk of AHCT595. Probably Fender having a job lot of the HCT rather than some on-the-edge of envelope AHCT spec requirement for this use. But as a backstop I now know the central in-tune LED only is an option with a 4015, without the flat and sharp direction LEDs. The main scale note LEDs are driven from another 595 To desolder the chip cover the line of LEDs with some axially sliced silicone sleeving / oven shelf edge covering before hot air desoldering If just a geeen in-tune LED and the coarse note LED above is sufficient then a 4025 will do with Q2 to green, Q0 to sw illuminator p11 of 595 to p9 p14 to p7 But without o/p latches the other LEDs flicker The second clock line supresses the flicker worked with a 74HC595 replacement for the 74AHCT595 Sp 7.5R 2 sizes of socket required to release the recessed control pot bush niuts Dart point to prise off the star washer clips off the plastic rods Make sure double row header is not displaced 1 row on reassembling the ribbon Reinforce discrete wire ribbons with hotmelt before removing boards over the sleeves as only over the wires and the wires break. Loss of wire next to the white LEDs leads to loss of tuner/timbre sw function. Fender Twin, 1999, ser no CR2636-- Bad hum above level 3 hum worse with i/p1 tank W to front, R to rear, R 1.5R, W 210R 2 caps C47 and C48 tarry splodgy mess from them , on the grey ribbon, touching them. Domed ends but no oily film , even on removal, olive brown colour IC RSSM marking 30mV DVM-ac noise on +16V zener, 1mV on -16V Z, browning of pcb Remove most ps pcb screws to bend back enough to remove caps and zeners. Extend the zeners and put a bend in so the zeners are off the board and away from the caps Replaced 2x 1000uF.35V with 105 deg C ones also with a set so away from the 5W resistors ESR was normal but capacities 70 and 80uF One valve base socket pin pulled out with the valve but only failur eof the tang that is supposed to stop this. Sp 15.1R V5 (from i/p V1) numbering was ECC83 not AT7, nothing noticed in use 15mV DVM-ac hum over the speakers at idle, down to 60Hz Tx in 50Hz use level of hum Converting 1964 Fender Twin Reverb amp for 240V UK use Cab had been dropped or squashed and amp would not release. Remove lamp lens and next 6 pot knobs and nuts to allow the front panel to bend without creasing. Measured the gap both ends, released screws and forced narrow gap with reversed sash cramp and tightened again. Mains Tx 125P34A 606443 choke 125C1A -606-4-45 op tx 125A 29A 606436 Of course the owner wants it to be as original as possible or at least retrievable. I've convinced him that a fully bonded earth point to the chassis is absolutely necessary for use in the UK, no getting away from that. Hopefully the US mains cable rubber insulation will be perished and will need replacing anyway so would then be 3 core. He definitely does not want the step down transformer mounted in the cab, but external . But if original US mains cable and US plug retained. I'm thinking earthing coloured multistrand flexible third cable run alongside the US cable with black heatshrink over the near-enough whole length. The problem is what connector to use for reliable earth continuity to the step down Tx and UK mains cable and how to make a mechanical interlock, in effect, so the amp cannot be run without the third wire connected. Then what to do with the original "ground" switch ? presumably disconnect but leave in place internally . Do US three pin variant outlet, purpose made, step down transformers exist in the UK, I only ever see 2 pin outlet ones. Assuming he can tolerate swapping, but retaining with the amp, the ancient 2 pin plug. All original inside except one resistor. 1964 Twin Reverb. I see US 3 pin outlet auto transformers are available. But owner wants to retain the moulded , sorry molded, 2 pin plug. All I can think of is making a 2 part shroud that fits overe the existing plug and includes a third earthing pin to mate with the 3 pin outlet, also retaining polarisation for added safety (assuming anyone rewiring the UK main plug in the future , wires it correctly). Third wire under heatshrink and bonded to the chassis mounted 110V outlet , removing the PK and replacing with a bolt and lock nut/star washer inside. Some sort of shrouding over the earth /chassis bond and exposed stub of wire. I'll try and convince him to go for isolating rather than auto but the original 2 pin plug plus grounding pin union problem remains. I really want to be able to condemn the mains lead. But the internal exposed sheathing looks fine, how to non-destructively check for internally mangled insulation or wiring filaments inside the cable strain relief? A possible face-saving route. Release the tethered 2 part mains cable strain relief, bend the cable back and forth at that strain point enough times and let the owner feel the floppy section. Then 3 core can go in place. Returning to plan A. What I think of as a lawnmower connector, 2 part outer shell. Just space to mould in the existing US plug and fix in a third pin. All demountable leaving the original cable and plug untouched, if so required. Then either black nylon spiral wrap or heatshrink over the green wire along the original cable. Satisfying the original brief but would be a lot cheaper for him just having 2 core cable replaced with 3 core and 3 pin plug, retained in the cab for any , unlikely, future USA based user. A couple of clinchnuts instead of the one closure fixing, for a now 2-section Black & Decker lawnmower connector and looks almost professional. Some IC or H section rubber grommet strip glued to one surface of the cut edge of the lawnmower connector. Razor the corners and then grind through the bulk of the material. Earthing pin set into the side , black epoxied and shrouded over IEC plug section, not quite so pro looking. Insulation test , 50M or so momentarily and then 1G or so due to the grounding cap when present Loose front panel Al plate . A grounding tag from something like a PL259 with the solder tag ground off is large enough to go over the lamp and under the dome to trap the panel. 6.5V replacement bulb is longer so required the mounting clamp to be bend inwards to amp for clearance under the lens dome or would break contact. Vibrato needs vibrato pedal pin to ground. Should see neon in opto coupler flashing orange. Tank one spring line broken. Beware nasty tarry gooey gluing top of tank to top of bag, neutralise with rtalc before getting it on your clothing. Metalised label on inside worn away by heavy handedness and springs rubbing against label. Subsidiary of Hammond Organ 1122 under the ink date stamp of 6444 Bend back one spring end 60 degrees to reinsert. Used doubled up tungsten wire as anchor on other end with some brown soft magnet shaped and glued over . Back off the spring tension before pulling the tungsten wires to final posistion and gluing off rather than solder as the cups on the brass barrels are a bit iffy if dislodged by melting the solder between and also avoids overheating and melting the plastic overall mount. Fender Twin Reverb , Converting 1960s amp for 240V UK use Of course the owner wants it to be as original as possible or at least retrievable. I've convinced him that a fully bonded earth point to the chassis is absolutely necessary for use in the UK, no getting away from that. Hopefully the US mains cable rubber insulation will be perished and will need replacing anyway so would then be 3 core. He definitely does not want the step down transformer mounted in the cab, but external . But if original US mains cable and US plug retained. I'm thinking earthing coloured multistrand flexible third cable run alongside the US cable with black heatshrink over the near-enough whole length. The problem is what connector to use for reliable earth continuity to the step down Tx and UK mains cable and how to make a mechanical interlock, in effect, so the amp cannot be run without the third wire connected. Then what to do with the original "ground" switch ? presumably disconnect but leave in place internally . Do US three pin variant outlet, purpose made, step down transformers exist in the UK, I only ever see 2 pin outlet ones. Assuming he can tolerate swapping, but retaining with the amp, the ancient 2 pin plug. All original inside except one resistor. 1964 Twin Reverb. I see US 3 pin outlet auto transformers are available. But owner wants to retain the moulded , sorry molded, 2 pin plug. All I can think of is making a 2 part shroud that fits overe the existing plug and includes a third earthing pin to mate with the 3 pin outlet, also retaining polarisation for added safety (assuming anyone rewiring the UK main plug in the future , wires it correctly). Third wire under heatshrink and bonded to the chassis mounted 110V outlet , removing the PK and replacing with a bolt and lock nut/star washer inside. Some sort of shrouding over the earth /chassis bond and exposed stub of wire. I'll try and convince him to go for isolating rather than auto but the original 2 pin plug plus grounding pin union problem remains. I really want to be able to condemn the mains lead. But the internal exposed sheathing looks fine, how to non-destructively check for internally mangled insulation or wiring filaments inside the cable strain relief? A possible face-saving route. Release the tethered 2 part mains cable strain relief, bend the cable back and forth at that strain point enough times and let the owner feel the floppy section. Then 3 core can go in place. Returning to plan A. What I think of as a lawnmower connector, 2 part outer shell. Black and Decker black connector sliced through the centre to make 2 wrap around shell parts. Just space to mould in the existing US plug and fix in a third pin. All demountable leaving the original cable and plug untouched, if so required. Then either black nylon spiral wrap or heatshrink over the green wire along the original cable. Decided on exposed earth wire and dyed Hellerman sleeving every 6 inches. Satisfying the original brief but would be a lot cheaper for him just having 2 core cable replaced with 3 core and 3 pin plug, retained in the cab for any , unlikely, future USA based user. A couple of clinchnuts instead of the one closure fixing, for a now 2-section Black & Decker lawnmower connector and looks almost professional. Earthing pin set into the side , black epoxied and shrouded over, not quite so pro looking. Bronze multistand wire over suitable round brass pin , ground a taper to fit the USA 3 pin socket better, let into the wiring clamp , bronze passed through holes made in th eB&D , then internally round the clinch nuts and twisted off to take soldered on earth wire . Prelimary epoxy to anchor the pin then next day the shrouding. For suitable shrouding piece used the angled outer part of an IEC line socket plug , cut down to suit. Covered the original USA plug in PTFE plumbers tape to fill the B&D halves with USA in place, in 2 operations to pad out with hotmelt glue. Earth wire taken to multiple solder tags fitted by new bolt and lock nuts to the original outlet socket fixings, leaving original screw fixed inside and while there disconected the grounding capacitor. The cab had been dropped or something so not possible to withdraw the amp without removing a few knobs and allowing the fron Al panel to bend a bit. With a metal block and feeler gauge the right hand end gap was 1.5mm less than the left. Slackened the internal battens on the shallow side and small vice and soft coverings opened up the slot using vice in reverse sense and screwed in battens again while gap is so stretched. A better job on the B&D demountable would have been girder section grommet fixed in the gap between the 2 halves. Step down auto transformer with USA 3 pin so. The third grounding pin seems to be always round and with no taper in any sense. The socket I have here has a ground-pin recess that is a conflation of a semicircle and half a square in cross section . Equally solid, ie no springing action. Or is there a taper down the length of the ground pin recess that I cannot gauge . I expected a round pin with a tapered flat and a slot along the length of the pin to give some sprung gripping/ latitude for dimensional inconsistency. Fender twin reverb - dog's breakfast Low level bacon and eggs noise and low level whistling kettle noise. Goes if V1 is pulled , no difference with change of valve V1. Noises disappear if no input and normal volume turned to maximum. Leaky DC decoupling cap between first and second triode ? you can play through a vib ip with no pedal sw and its fine, so not a V2.....onwards problem Seems odd that varying the associated tone controls has no effect on the whistle tone or level The HV side corner of the board , not the nearby cap wires, is extremely microphonic. Only mV DC lowside of the .1 and .047 uF caps . Removing the fixing screw through the whale-hide or whatever junk that passed for circuit board then, does seem to stop the noises. Some thin FRPB will go between the 2 bits of whale-hide and an insulated collar under a longer screw will go back through there. Consistent 2 to 3 volts on DVM probe around the edge of the whale hide normal ? The previous time I've come across this was with a Fender Concert and then I put it down to someone previously soldering a component with the "active" board in situ and had burnt part of the grounded whale-hide sheet underneath. Placing some extra insulation cured that time also. So anyone know precisely what the failure is . Presumably taking up humidity but what next? salts in the material forming a conductive path in the core of the material. I will try a megger on the material when I next get to the amp , no problem seen on external surfaces with a 30M DVM. And what is that stuff? whale-hide? artificial leather ? probably vulcanised fish-paper Under 30x magnification and some lighting did not look fibrous or patterned in any way. Nothing observable with a Megger and a couple of needles pushed into the edge. Next time I come across some of it I'll burn a sample - unmistakable smell if phenolic or rubber and inspect the broken edge under x30 and higher. This is what the board looks like and as it is used, colour is correct Will quite readily bend when cold , say .5 inch displacement over a 2 inch run although something like 1/8 inch thick Because of its microphonic behaviour I suspect some sort of capacitance efffect. Hinted at by it only seems necessary to separate the "active" board and the backing insulation "grounded" board to stop the rustle and microphony. More permanent fix by securing some rigid paxolin FRPB between the 2 boards. I suspect something in the core of the material goes conductive enough to create a capacitor surface around high voltage points. I had also assumed the problem although initially through humidity take-up , the rustling (rather than a louder crackling ) problem, I could only see as microscopic discharges somewhere in the core of the material. Separating the 2 boards with PRFB and insulating the fixing screw that passes between the 2 stops it , presumably because the pd through the short run of board to the ground is now a longer path - not cured , just delayed. If you knew where the conductive paths were , it may be possible to route/grind slots into the board to cure or preclude these problems Monitoring tone caps for mains of 75 percent and 215V on V1 anode .1uF cap 9mV dc downstream, .077uF 1mV, 470pF 70 to 85 mV on varying vol pot The low-level whistling kettle returned but went on tapping V2 , needed replacing also canal boat noise when tremolo engaged but no input needed V6 replacing, accidently put an ecc83 in there and the effect was much worse. Fender Twin reverb from 1979 Assuming I cannot get 1.5 inch long UNC 8/32 bolts in the UK, other than a hundred or stupid min order quotes. I cannot return this amp , despite repair, as it is unsafe. The 4 vertically mounted screws that litterally hold the amp into the cab are stripped to next to useless. Not captive nuts , nor spire nuts in the chassis part, sort of combination of both. Stamped something like CIP-MUL 832 54 950 / 075 So either woodwork fitting battens along the sides to support amp should what is left of the screwthreads fail, but amp would be loose then, but not fall out as such. Or fit metric captive nuts into the chassis and replace the screws with metric. Or any other work-around suggestions. I'm not interested in purists opinions , decrying non-originality. The owners mistreat the amp and can keep the originals along with the all too tempting-to-turn rear voltage selector knob . Fine for USA but out and out safety hazzard in the UK, especially the way this lot abuse their kit. Removed and plated off over the spindle and knob fitted internally inside the amp for any later purists. Not enough thread for a spindle lock. I've found some 4mm captive/caged nuts, that with a bit of coaxing will go into the existing holes in the chassis without enlarging. And 4mm stainless steel bolts of the right length. The 3 screws at the rear are into cabinet wood that may as well be made of paper as far as resisting the weight of 2 large transformers + + in a cantilever action. I'd have more confidence in those 3 wood screws at the rear of the chassis, into the cab top, if they were longer and set at at opposing angles a la floor-board nails, for maximum resistance to being pulled out BTW that decayed horse manure or goaty smell inside the amp . What is it they add to winding wire insulation in the US that biologically breaks down with UK damp air or whatever is the cause. No particularly unpleasant but I'd rather the workshop smelled of bakelite or shellac say, rather than a farmyard. The fourth such instance of this USA originated smell. Overall length 37mm . Width of cab and spreader plates 25mm , 2mm chassis thickness leaving you with 37 mm long bolts. Cement R 28K, 2.53K in cct ESR measurements under metal cover (10V range) .25,.22,1.6,2,1.2,.9,,5, always seems too much background hum with these sorts of amps but valves and caps seem good and "hum balance" makes no difference. Background hum measured over the speakers at 12mV with DVM It would be possible to add more cap insoide the box by raising on pillars and a wall of metal sheet around. Mains tr primary 100V 5.1R, 120V 5.2, 127 5.3R, 220V 6.4, 240 6.6, 260 7.1R secondaries .1R, 6.6R, 2.6R (no vlaves present) Speakers , both reconed by Wembley measured 3.2R lead from vol control to valve sensitive to touching. Holding wire to chassis with piece of wood near the valve base and tapping the wire vol end , same effect so capacitive effect of wire not valve problem. 4.5R,32.5R, & ,36,5.4R output tr ? Reverb tank corrossion on output phono socket , breaking ground contact and previous repair where someone had just reconnected one of the springs to a wire but no magnet. i/p 1R ,1.18mH about 66T of .26mm wire// op 153R ,338mF Soft brown ferrite magnet material , as it is easily cut with a razor to make 2 parts to go over the wire suspension and through the anchor assembly , required to be about 2mm diameter and 4mm long . Came from a 4 pole multipole motor from a scrapped early VCR, before rare earth magnets came in. But also seen on fridge magnets and that flexible metal noticeboard magnets. This one a ring about 85mm diameter from a brushless DC VCR motor. Checked the original on the other end with a simple magnetic compass. At 270 degrees it deflected north by 25 degrees. Replacement magnet about 75 degree swing. Find the orientation of maximum magnetism , mark , for later orientation nearest a pole piece. Cut 2 "halves" one larger and cut a groove down the centre with Dremmel and half mm disc and glued around the piece of nichrome heater wire for spring anchor hook. into the amp the Rs measured 0.9R and 244K .9R ,1760,28.2K for the reverb transformer Checking remade springline only .58V ac at 3KHz (DVM) over 1R gave 0.012V over 8R via a bench amplifier original one with same i/p gave .003V over 6R with sig gen 3KHz 0,5mV fed in directly over .9R into the amp gave 0.042V over 8R Grey and red phono leads swap colours Fischer in ear amplifier, 2005 Used by drummer for sync beats from keyboardist Dropped and then mains arcing and sparking , intermittant failure Handscrawled in white on laptop sort of smps, 30W . Presumably bought in by Fischer Selectable between 12V and 24V by external (but inside the amp casing) selector slide switch , other marking is ATPS 2324, about 2005 probably Ansmann atps 2324 before branding up, bought in bulk by Fischer "Cassette" lead socket only relying on now failed solder points despite 2 holes in the pcb for some sort of fixing. Ball milled out the holes a bit to be able to take daisy-chained pair of smallest cable ties. noting unusual device in amp TI TLE2062CP Plectrum into smps casing at the slider slot efge where it is weakest. 4 clips approx 15mm from each end on long sides. To refit over slider , move slider to 12V end ,so you can see to refit and then revert to 24V when encased again. 12-24V setting is on undeside , when mounted in the shoe. This lasted a year but then socket failed again. Blanked off the original inlet and cut a slot between 1/4 in outlet and shoe for the ps. Wired in with double insulated wire to the ps pcb solder points Fuchs Plush Good Verbrations, 2009 "You don't belong here" printed on the overlay- so thats why its fuched. Proudly says RoHS on the casing, rustling noises at random, so fuched by RoHS probably, certainly PbF solder. How to get under the scrappy looking black "conformal" coating. wire brush in Dremmel then scalpel between pins and then needle, hooked it off quite cleanly. Not epoxy coating as methylated spirit softened this plasticky coating enough to scrape off with a wooden cocktail stick on the Main chip Spin FV-1 , nice to see datasheet for this on their site , and also 5532. Logo like half a swastika in a circle. Seems suspect solder on a pin of the main chip, from twizzle sticking. But what is the cleanest way to get the coating off - it hardly looks pretty as it is, am concerned about meths migrating capilliary fashion along the pins, to deal with the underlying pbfitis. Chemical reaction between this black stuff and solder? 1/2 inch 25TPI bush nut missing C10.C11 3.3uF , one lifted off pcb on picking off the black stuff. Mark the power socket before removing as its a bodge up. What an overpriced heap of junk. On pulling off this rubbery plastic film one of the SM caps came off with it. The film is not stuck to the components with any force, a needle under it and it lifts quite easily off pcb etc except where its lodged between IC pins. The SM C&R near the main chip that I had wire brushed were firm enough. Poor PbF solder under pin 22 was the main problem but what else lurks under the rest of the black stuff I've not touched? Standard die cast box with no bumpons under to stop it sliding, no separate battery housing so you have to fully open up to replace battery . The power socket loose and no 1/2 inch 25 TPI bush nut available this side of the pond, to rob off something, to replace it, maker had hand filed out hole in the box to receive the socket (because of flats). Looks as though I'll have to continue the spirit of bodge, with hotmelt glue inside to keep this socket in place. Gallien Kruegar Backline 100, 1992 footswitch functions worked from amp but not via footswitch maybe due to 12mm long piece of cropped lead laying insid ethe amp - maybe had been resting over the footsw pcb contacts, turning amp on its side to extract from cab dislodged it Tank W55 sp 7.3R, Paragon VL-100 knobs RRGEEREEEWW Ring nuts and star washers inside for black plastic stem pots, joggled pins, one broke on desoldering. Pots logo "T and slim S in a circle" . Remove back and move wiper segments . Double ones , enough room to use needlepoints to restress the wipers . Remove excess grease 270-30416 39/9138 ROC black spindles 91 probably date 1991 , need the pins offset to match holes. Tx for UK Y,Gn,Bn, O, W,-,-, R, R Be Be,P,Gn PA 4x .16R, 2x .33R 5W 2x 220 5W 2x TIP35C, 2x TIP36C, LF353 ITT blue and white miniature DPDT sw shape sw bad. Unclip white locking yoke , contract the spring fitted over the paxolin to release the blue section PA , no load TOP3 .6,43,.05Vdc -.49,-43,+.04 Q76 .6,42.6,1.2 Q63 42.2,1.2,41.6 Q30, -42.3, -1.1, -41.7 Q51, -1.1, middle pin only measured Check the front pannel sw work , had to open one of the square holes for reliable action Gallien Krueger MB150E - III, 2005 crackle on o/p Speaker RoHS but amp escaped Speaker 5.2R, stable ac current under load with prodding through grill and cone not cut into as problem probably on diverter sw solder on return 1/4 in socket or corrossion on contacts, added silicone sleeving to tension up Remove 2x4 screws at top end faces to release amp 1R, 8x2.2R, 2x C5242,337T, 317T, C4793, some TO126 and 5 devices underneath unseen. One 3mm screw holding TOP3 to h/s had bad /stripped/cross threaded tapped hole in the Al, replaced with a longer bolt to engage fresh tapping Bad level pot, stereo. These are log of a curvey F. in a circle. The resistive wiper is integral with the common wiper , vey close together , something to do with hte problem but not fully resolved. Internal metal projection divides the 2 sections and needs to be negotiated around the divided plastic to reassemble. Returned a few years later after some stage gear fell on it, broken i/p socket and bush part of Vol and Treble pots broken away from body. Sometimes excessive hiss, sometimes a load of hum Use ext sp so for test and its sw Vol 50K , A, replaced with A100K, 50KB replaced. Wired in replacement i/p socket , requiring moving a small electro to the other side of the pcb Gibson Les Paul, 2003, tobacco finish Output from guitar noticeably dropped in level , owner had a spare one to complete the set. When I received it , setting both vol pots to minimum then ohmage across output was 30 ohm. Now I'm inside, it is 3 to 5 ohms according to switch setting. Pickup ohmages measure 7.82,3.80, 7.39K at the 3 switch settings, which seems right, and consistent with wire tugs. Now the bottom ohmage of the pots was not going to be 60 and 60 ohm or so to give 30, one poor pot perhaps. I will remove the output screened lead although nothing seems wrong with it, but the output socket was loose and turning to an extentm requiting the screened lead to resist the turning. Just leaves wear /plating problem at the tip contact of the switchcraft 1/4 in socket but it looks perfectly normal, contact point axial to jack until deflected to the tip groove , etc. Pots measure consistent across tracks. Switch seems ok but how to test other than by replacement. Tugging on the screen leads to the pickups did not change the DC ohmages so I left them be and all those adjustments . Reluctant to knock the pickup bodies to test for intermittant wire break. From the 8 figure serial number this was probably mid 2003 but I doubt Gibson would use computer data cable to the switch, presumably someone replaced it. The foil sheathing of that, at the end, was floating in space and could have touched the signal out line, The "cloth" core of the sig out wire was disrupted where the earthing braid is soldered to the switchcraft socket and being loose, turned. As turning a jack in there, there was a poor-conductive point to the contact so perhaps a build up of sprayed in WD40 leading to that and a bit of conduction at the core fraying. If I owned one of these I'd ditch that silly plastic output escutchion and replace with a brass plate and 4 larger screws. Hairline stress cracks to each of the 4 mounting holes in that plastic and will fail soon - all the guitar lead yanking having to be restrained by that plastic square along with the bush nut localised stress. If they did not compress the braid of the screening , before soldering , then there would be less likelihood of problems with that old-style lacquered "hosiery" cloth insulation. Perhaps like the plastic escutchion, deliberate built-in pitfalls, having no justification otherwise. Told the owner if it happened again to try with sw in all 3 posistions if low /same low level / nothing then it would be a broken pickup. On receiving top pot 7.82/30/30R at minumum bottom vol pot 30/30/7.38K I did not think to check ground line from o/p so. to internal grounding but probably ok With sw in mid parallel position. With one pot at max and then maximum reading of wiper to ground on turning 6.9K wiper of lower vol pot 7.2K max for upper pot wiper To release the o/p signal lead. Desolder the core ends , straighten out the tag board end , desolder from the internal tag strip while pulling on the lead. Grind with .5mm disc into the braid solder at both ends , nearly to the cloth core and then a blade to open out the slot. Leave the output end partially soldered to the so. terminal Pull out the hosiery core , reuse if not too bad the other way round , replace , stretch then lacquer over. Reinsert into the metal brading. Bend away the filaments and don't tighten onto the core but use hot melt glue to bind in place after resoldering into the tag board . Glued the floating end of the someone else's data cable to something solid, earthing was ok. Cloth core 1.4 mm diameter . Compress the metal sheath toi reinsert the core and then stretch over afterwards, pushing , not pulling. Gougeon DS French made but not design build of a Citroen DS. Almost a googlewhack , but just on the off chance anyone here has any info. Digital spot effects generator c 1990, chippery info has been ground off, hopefully just heavy use and mechanical failings. Arret and Marche on the mains switch labelling. No mains earth grounding. 240V transformer 16-12-0-12-16V, 1530R/65R (over used taps) 12.5 - 32 BD139 Siemens SFH609-2 for the balanced output lines LM340T5, 7812, D27C0120 eprom + micro plus 2. 10K log . Broken mains switch and broken front panel overlay interferring with the switches so cut out circles. Sorted out ground and blanked off unused IEC holes Repaired it and pressed a button, expecting a siren or machine-gun noise. No a sexy-voiced French girl saying oh la la! Haffner 1960s guitar pick up maybe colourama? No ohms on measuring , probably C inside. Scope showed good signal with tuning fork and DVM ac of 50mV or more. Gemini GXA 1600, 2004?, not PbF One bad ch, tapping on the top would temp cure Airflow in is the long thin slot along the top and bottom of the front panel, clogged with dust, used with amp fixed vertically. To remove rear panel , leave the speakon sc. Bend fan baffle plates a bit inwards to give space to move. Move main pcb forwards after releasing 3x m/s, 2 under and 1 inside and 2ec pk on the H/s. On sides large and small m/s to basecover. 1 internal sc to pcb at least on repowering refit 2 standoffs that drop away under pcb 2SC5200, 2SA1943 Stereo sw problem chB , 4P 3W, removed and renovated 2 distinct relay clicks, 1 for each ch Main pcb , with h/s on sided , makes narrow centre section vulnerable, so support while moving Mascot Gemini FM 64, 2005 (with UF 2064 receiver) 845-865MHz UHF I found the secret screw under the ch/gr label. No LED and no output. I was hoping it was a broken switch as the plastic slide-knob is missing and they had been using a screwdriver, in there ,to the slide-sw stub for on/off. As it is nearer mobile phone circuitry in there, ? 2P3W switch action seems ok and battery connections ok. GR = frequency sub-group Looks a right mess under a 30x. They must have screwdrivered it hundreds of times before neatly prizing off a SMD SOT23, leaving 3 non-virgin pads. First guess topmark LG like most of them around , NPN yes, my list says UHF BF775 - unlikely . Will try anything GP that is NPN , pin1 68K to it is assumed base, p2 gnd E, p3 1k so C assumed. For completeness LG = ? Other SO23 are SOT23 FET probably , marked XY NPN SOT23 marked FV then sideways 18 small script, probable pinning p1 E, p2 C, p3 B if anyone has topmarks for about 2005 It would seem to be a mangled DC power connector for rechargeable batteries option and one of the traces from it is zigzagged and UHF overlain on it for radiating out. The mating receiver is in a fixed installation Gemini FM 64 radio mike Soldered in a GP SOT23, BCW31 topcode D1. On 3V the LED flashes on switch on, and goes continuous if V drops to 1.4V and current goes well over 100mA before that. With 3V, current draw is 69mA and 68mA without the electret mike plugged in but no change in draw with tapping of mike. Nothing on the LM317 so I will assume that is for DC feed for rechargeables, not used for the main circuitry. Dug out an ancient early portable colour TV, retained for just such a purpose. So old it has a VHF rotary tuner built in as well as UHF. But of course nice old mechanical rotation for VT to tuner block, so can play around as much as you like detuning either side to try and get some sort of audio demodulated. At the top of the range around ch 68 a strong signal including interference pattern on picture,from the other end of the room, all going on switching off the radio mike. No amount of fiddling of de-tune would get even a semblance of sound on tapping the mike nor change of interference pattern on screen. At this stage without proper test equipment I will assume working entirely until the owner tells me otherwise. Still don't know what the third position of the slide switch is. Maybe only 2 positions used of the 3, going by the length of slot in the outer bezel, but the plastic widget that extends up from the pcb slide sw is missing, hence plenty of space to scrape a screwdriver around inside. The surround Al of the slide sw was so randomly scraped I thought it was brush finished when I first saw it, hence probably hundreds of screwdriver activations. Now to bodge up a widget Made a widget from a bit of VHS tape cassette outer, kids plastic mosaic bead, cutdown plastic snap rivet, hotmelt glue and some silicone paste so it slides easily and looks almost proper-like , original never seen. UHF TV test does work to the extent you can de-tune to a point where tapping on the mike will modulate the interference pattern on the screen and at another point a feint tapping in the audio. Sw is off/carrier on/carrier plus modulation, centre may be carrier plus pilot tone for interference nullification (mutes audio at receiver if pilot not received) The gr/ch numbers do not agree with the numbers marked on the codeswitches, under the label 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. Gibson Les Paul , Epiphone, ser no I001201** Sleve contact loose, ball bearing and vice tightened up but needed soldering togeher. Small return added to tip contact then O ring placed over and around the body, wired into place. Don't bend out the tags as will foul on the guitsar body Grainger Amps (China) see also Epiphone and Legacy Grainger Firebird 100H guitar amp, 2007 Fine until a week before and then crackle started immediately and was from then on unusable, rather than a build up from occassional RoHS and tick N222 stickers on the back and and so the problem is the usual for that . But unusually the phrasing with it is "Made in P.R. China". Bought by the owner from new. The idents on the overlays on the pcbs have been scratched off. The paper label over the Asic/Pic on the digital board has been scratched off. Also on that daughter board SMD IC with bogus Philips logo. Badly done re-work on traces to a 15V regulator at some point. Seconds/failed-test boards coming through a back-door from ,say, Peavey production line and sold on ? Rebadged/grey market? Epiphone Triggerman 100H I wonder what the internal build quality of the relays are , maker's names Good Sky and Hui Ke. So far 3 problems in the PREA found plus one made by me in the process of removing GND1 crimp spade (more solder on the contact side, than the solder side , bled through from the wiring side, ground back surface of trace around , loop of tinned wire around the tag pins of replacement pcb blade and goodly amount of solder) and of course I will have to demount the PA for pre-amptive dealing with the "usual suspects" solderings there. The digital effects includes reverb/delay . Not just that faux SMD Philips but some other SMD chip with pins bent-fomed under but adequate lands for solder so left untouched, just put alternating sets to the long header pins before refiting the subboard. Crackling all the time , particularly moving master volume or touching near it. Removing blue signal lead and crackling from speaker goes. Removed and no wear, poor wiper contact , tried circle of 1mm card between paxolin and diecast metal to pack out, with central hole and radial slot for placement. A1695, C4468, A1668 , C4382 on PA, 2x 6K8, 4R7, 470R, 2x5W R33 PREA 7x 4580D ch 1 level pot , loose trace to wiper 7815 badly reworked traces. 7815 and 7805 pots A250K,B100K,A250K,B100K,A25K,B100K, B10K,A5K A25K,B50K,A5K (MV) Tx 6.1R // R 0.9R, Y 3.1R More bodged rework under the PA. With blue signal wire removed (PREA to PA) there is crackle on phones Crackley master vol pot seems to be due to DC getting on the wiper, not from either end of the pot track or either end of the 47uF/63V but coming out of a 4580 dual opamp input , when varying the pot . In hindsight the giveaway was the sudden onset of very serious cone thumping bangs rather than crackle. It is directly connected to the wiper so perhaps a few hundred ohm should go in line as well as a new IC. The pot track was bad so perhaps with some DC getting through a blocking cap was enough to disrupt the IC input. Horrendous DC bangs have gone , replacing that 4580 with TL072. Maybe both op-amps set as unity-gain followers is something to do with the failure. Also replaced the 47uF, 63V electro and wire link to MV wiper with 200R. Have to replace both treble pots before I'm in a position to comparitive check the f-resp with 200R and shorted but seems ok just monitoring the output audibly. No observable (to .2% measurement) difference, 200R or 0R, 50 Hz to 10KHz. If the opamp failure was due to excess dV/dt then I doubt it would stop it recurring with a bad pot /cap in the future So of course Epiphone Triggerman 100H would likely be susceptible to the same failure, whatever precisely caused it. Thermal TO92 needs pushing back to the PA h/s 2 fibre washers per .25" Remove the white goo under the h/s Con 2A connects to Con 2B The alpha pots on this amp seem to be unreliable due to loss of contacts between conductive ring and wipers rather than resistive track wipers. Ar26 pins 5&6 (plus 7 in a sense) are untied / floating PREA and all leads to the PA disconnected except AC supply and a temp ground to main caps common, no speaker load. Thermal TO92 , end pins only +/-1V each Q39 -60.6V, -1,-61.1 Q35 -1,-61.4,-.5 Q32 TO92 61.4,60.9,60.4 Q33 60.4,1,60.4 Q310 1,61.4,.5 R319 -.46V / .5V .05V ac 400Hz in , pots at 1/2, DSP out, 2.1V over 8R PA more bodged rework. Alpha pots needed attention to the metal/metal contacts, relived spring tension. GuitarTech pickup 6.43K Broken tiny concentric connector. Removed and soldered a small solder tag on the inside for strain relief and screened lead out. As owner wished to change leads/pickups , lead out to 2x brass cores from 3 amp chock blocks , Hellerman sleeving with one hole punched for screwdriver access, covered over each , and some heatshrink to cover over the join 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 , see also under Samson for schematics Hartke Bass amp ? C2238A with one valve and conventional transformer , A968? PA 4.7R, 270 (discoloured to red purple and black) ,1.2K 10K, 4x .47 thermistor 22K NTC, in cct 2SB1429, 2SD2155 prea 10x 3, 33 A/R fault, well that is what Avo calls it, I've never come across one before. ECC83 with curious cyclic swirling breaking-surf whitish-noise and clicks. Putting on Avo 160 tester showed <>short in A/R setting, I've never had before, A/R here stands for cold checking Anodes To Remaining electrodes. DVM cold resistance checking pin to pin showed about 9K between an anode and its grid. I will replace it but is there any point in blasting with some high voltage to vaporize whatever is bridging, for a known unreliable/short-term spare. I'm aware that a valve with leaky C to H, then running the valve with 10 or 12V on the heaters insted of 6.3V so they glow like bulbs for a few seconds, will knock back the bridging deposit for a few months or even years. I've seriously banged the envelope and heated it with hot air and the resistance has hardly moved from 8.7K ohm. C/H leakage I've never seen below about 100K IIRC and was highly variable on knocking the envelope. 60V bench supply over A-G, dropped the resistance to 4.6K . Tried on a 500V Megger, not expecting to do much as only battery powered. Small white flash from inside and ohmage shot up to over 200M. Testing on valve tester and checks out fine load test .05V 400Hz in with all controls mid and sw out , 6.7V ac over 4R Hartke A70 Combo, 2006 High f squeel the owner could cut out by dropping the 5K graphic to bottom. With graphic as normal he also found that touching 1/4 inch jack ring to chassis would stop it. Of couse no appearance in my hands. Mains ground is properly bonded to chassis, I've not yet found where amp 0 is connected to chassis though it is (at the moment) , insulated bush 1/4 inch jacks throughout. Known issue with these ? I'm assuming the crosslink point, wherever it lies, is lifting intermittently. I note the coachbolt through the toroid is not making electrical contact to the chassis , thru the paint , so maybe similar wherever the amp ground is , DI XLR con perhaps. Ground crosslinking under the 2 input sockets via inadequate "star washer" metal and paint not scraped off the casing , bush nuts not loose just not fully tight , more than finger tight, enough slack to make intermittant I suppose . Ground off paint around both input socket "star washers" Early China PbF so lots of nasty heatsinky solder points, laying in wait, to rework, especially as pcb holes are far bigger than the leads in most cases. Once again rigid chassis fixed heatsink and o/p devices fixed to free-to-resonate pcb so a fillet of hot melt above and below at the join to dampen and cross-fix by more than just PbF solder points. No mention of PbF on boards or green warning stickers. One saving grace none of that waste of time and space white-goo between heatsink and casing to remove, before working on the board. 2x10R, 270,2x240R, 2x.22R, 1W 880,430,10K,15K, 680, 220,470,10K, 680,470, 220,3K3,2K2, 2x 150, 680 13700D, TIP42C TIP41C, D600K, D718, B688 ?, 7815.7915 mains tr 31.7-0-31.7 , 21R// 1.7R , Be-Be 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 derived) 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 Hartke LH500, 2008, RoHS Volume dropped after hour of use For schematic search on Samson LH1000 How to remove the preamp board? Looks as though it should come away with the front sub-panel, leaving front panel in place. But something near the valve base is holding it in place. Oddly 1 fixing only for the screening can mounting base (diametric one is floating ,by "design"), looks like a rivet but is it some sort of push-on stud fitting? I don't want to strain it if its not. Otherwise to remove the front panel requires removing the PA to get to one of the screws holding the rack handles in place. Schematic on Elektrotanya, as Samson LH1000 In the light of this one I will have to change my PbF attack procedure - I will have to find a feather. Reported symptom intermittant drop in volume. No problem on me powering it up. Removed top cover and twizzling lightly with ballpoint barrel, the output dropped out and back on touching the prea-pa signal cable. Never occured since with harder prodding / tapping/ tugging at the adjascent "header" cable termination, so I must have mechanically closed the solder break, for the moment. From now on with PbF , first twizzling will be litterally with a feather I think. Deliberately made awkward. On reassembly the screws will go up from under into the alternative existing unused vertical threaded holes of the front sub panel. With a torch and mirror there are 2 screws access under the pcb, horizontally threaded. The one under the treble control requires undoing the toroid's coachbolt to get to. Even then required putting a pozi headed hex piece inside a nut driver to be long and narrow enough to get to it. The end one is ok when you know it is there. Lightly touched wire to CN3 the pre to pa lead and o/p cut out. With further tugging did not recur , probably suspect crimping so soldered up and dealt with usual PbF suspects while in there. Add 240/120V select sw movement inhibitor Don't forget padding rings on sub-front panel. Front dust filter unclips from outside , replace under edge first TC Helicon Voicelive stomp box thing, 2006 Movement sensing to mode switching query. Very sensitive to vibration, dropping into mixer setting away from voice mode without touching any pot or control. 2006 , PbF but no mention anywhere, output level pot seemed to be the most sensitive, logical as most used one. Solder yucky and partially-cracked (that river ravine type appearance ) but not obviously failed joints at the pins under x30 , but as pots, cannot sensibly do a tug test. Redid solder on all pots and most of the heatsinky joints on that board and replaced vol pot. No pots showed anything amiss monitoring wiper V or R and knocking. Anyway much improved but a serious knock to the board, not the pots themselves will trigger mixer mode. Setting any pot to half and paralleling an insulated (not fingering as induced stray will trigger) R to it then 100K // to half 10K will trigger MIX mode but not 390K // 5K so trigger delta R is about 2 or 3 percent , is this normal , low? any sort of standard for this pot-swiching action trigger level? Adding C at the pots does not seem to be an option - latches up the sensing, unless a very specific amount between 10n and 330nF , so far only tried Nothing flashes up, differentially, in the display but I suppose I should have noted the readings as set before to notice a change - next time I come across this sort of fault. I've settled for sometime a heavy tap with a large screwdriver handle to the edge of the pcb triggering mode change rather than most times a light tap with a ballpoint barrel as being as it should be. Wrapped up for them for a practise session this evening, will see if it bounces. 3.3V on pots, output wiper to p12 of Atmel processor ps fuse 1A at rear of ps Sicha 94V0 30K, 47,10,200,470 JKS020Q1, 2SK2625, thermistor 16R NTC TC helicon voicelive2, 2009? If it was a synthesiser you would think it was a stuck key. Continuous cyclic racket, sounding like a swarm of hornets, mosquitos and bagpipes with chorus effect thrown in. Presumably DSP problem. Changing buttons etc changes the character of the noise and the display functions normally. Only got in far enough to see a RED LED flashing fast and regular but slightly modulated I think, and noise does not vary with twizzling. I'll take a recording of it before full disassemly, in case it is diagnostic The effect is on harmonize and double functions only , recorded for reference. No different whether ground lift button is activated or not and whether a proper ground connection is made and the LED flashes all the time. It is full level intrusion , not background level. When the distortion is there it emerges after POST or not present after POST and stays in that state till switch off. When present there is a phasing stereo image of it on the phones output and adding smoothing to the DC input or adding a true grounding makes no difference. Of course no way of forcing the outcome one way or another at switch on, because that would indicate where the problem was. Sometimes R ch is just crackle in sympathy with the full noise on the L ch. When not present and adding a badly screened mic input and the gain turned up then a similar sort of noise gets in as background hash. Time to take the unit apart fully same old digital rigmarole. No scrubbed idents and datasheets for everything probably, including the DSP. Other than close inspection of soldering, checking 1V and 3.3V supplies and grounds and any poer-on-reset devices not much else other than random insulated SMD squashing and lead tugging etc at power-on, thats all that can sensibly be done. I will try tracing the didtortion back to a possible origin, assuming with the boards opened out probable, the distortion returns. Perhaps a reset problem. Touching header J301 p10 with a probe, kills the noise and normal function seems to resume. The LD1 red LED flashing seems to be normal function. AT POST the sequence is 2 second off, 1.5 sec flashing, 1.5 sec off, then continuous flashing. Finger injection of EMI the noise goes immediately and flashing LED goes off for 2 sec, 1.5 sec on, then continous flashing. p10 connects round the houses of the DSP board via a jumpered J101 for some other option, to what I assume is some sort of control processor with 32M of memory, has Helicon label v1.2.01 on it. Under is Spansion S29AL032 then looks like 070TF103. Datasheet not found on but their numbering seems to be letter not 0 (or O) after the 032, but suffix TF103 part is similar to other devices of theirs. Will trace the other way to the display board which is still in the casing seems to be s29al032D70TF103 Assuming pinning of S29AL016M is the same, then pin12 is a reset. Removing the 2 top boards, the system micro is a ATMEGA 88 20AU on the underside of the board. The "EMI reset" goes to p32 of that, which is an input also, so perhaps a flakey long period reset IC/ electrolytic somewhere. The 3 electros on the top board ESR'd ok and not connected to that line anyway Remove base and side cheeks . Adding cap to DC supply makes no difference to sturtup buzz, same with a true ground and also running from a 12V battery. Turning up the output level, when the unit is working properly, and a poorly screened mic lead as input then similar hash noise. Sometimes the R ch out is just crackle in sympathy with the peaks of the buzz hash on the L ch. DSPB56720AG LD1 flashes about 1.5 sec, 1.5 sec off, then on continuous in buzz situation With no buzz the LD1 sequence is 2sec off, 1.5 sec on, then flashing continuously. The reset line goes around the houses to Spansion S29AL032D70TF103, p12, labelled V1.2.01 via jumper J101 at rear Ti TAS02B 08W, 40pin Remove 4+1 knobs, then all sc to remove both top boards, beware sw caps are not tightly captive and ends of the casing need to be a bit loose to manoevre boards out L5970D is for 3.3V EMI reset line to DSP p111 via R1 of 33R 3.15V on p10 of the ribbon 0.97V on DSP p1 5V on LM317 h/s, 9.2V supply F800 at DC in is marked TN Ground Lift disconnects 2x XLR and 2x 1/4 inch from DC 0V Frame gnd stays with MIC connector shrouds 2 gnd points with chromed sc connecting sw panep pcb to plastic have metal contacts buried in the plastic to connect to casing. DSP board gnd at USB socket. ps and analogue pcb edge springs, open out before reassembly and all other contacts check for goodness. All electros ESR'd ok Settled on 100K pull up to from ribbon p10 to 3.3V plane near U306 and 4.7uF to gnd at the rear 0 ohm jumper point. Even so sometimes with a mic connected at sw on, then buzz 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 MA100, 1974 wavering volume mains tr 12R rear board ground wire broken and loose TO5 devices, failed solder. 2x 2N5415, STA5141, 2x2N3440,2x BC204B, replacements? ZTX753, ZTX653, LM358, 14 pin 741 Logo on this and the other contemporaneous TO5 of 2N3440 and 2N5415 is indistinct that at first sight looks like curvey M but is STT or SIT or STI with shaded and sloping capital letters melded together I cannot be sure it is STT logo, I would not say it was STC , no C at the end. There was an STC STA9... range. Anyway for anyone meeting one in earnest it is TO3, NPN, "D" pinning EBC and probably 300V rating like the others in that area HH , logo H||H on my screen H 2 vertical bars H I decided to remove the cover on the output pair and the same shaded logo there reads definitely STC, so presumably before the rasterfied form of their logo. TO3 devices marked 9029 and date code also 7429 That 'dropped' piece of white in the TO5 logo stamps , at the end is consistent on all of the TO5 so perhaps a broken stamp The STA 5141marked device is in an awkward position to photo. Remnant of H&H I think is printed on the front Al girder, so not a different company. When was the last time anyone saw a fully working ZnS electrophosphorescent panel on these (not HA100) MA100 amps? Is the oily feel but not oily smelling coating over the boards inside , broken down conformal coating, or owner squirting Snibbo (Spike Milligan TM) everywhere. Was it US STC = Silicon Transistor Corporation or UK STC Standard Telephones and Cables interesting info different logo again I picked up my 1976 D.A.T.A transistor book , back face up and it has on the back, a full page ad for Silicon Transistor Corporation devices, with that logo (undisplaced C-top) but no reference to those sorts of numbers on that page or inside pages. Maybe export versions. Page from short form catalog STC was acquired by New England Semiconductor and then by Microsemi Reverb tank 168R/170R 25K log track orn to 38K Dabs of lacquer on rear board retaining nuts Before removing then get access to pots,1/4 in, sw Heatsink symbol on overlay of Q2 but now ZTX753 Q5 and Q7 now have added h/s Q6 STA... , Q5 3440,Q7 5415 Desolder earth wire of pa board before removing Beware 4 wires to some pots 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. A solution would probably be a pair of computer "go faster" cold cathode tubes and inverter off 12V dropped from main supply. Or slimline 468mm long fluorescent tube with the guts of a CFL in the body of the amp, an 11W CFL cct will drive a 16W 468mm straight tube, 8W may be more suitable. Then some translucent neon green sticky-backed book covering covering it or floodlight gel or coloured lacquer/varnish. High voltage wiring to the tube and screening for EMC issues. 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, remove rear panel and rotate to pass back through the casing and remove both front and back through the front. Hold , for working on, with 4 tapped rods no more than 8 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 On another occassion for pot replacement No send/return bypass sw problems as standard toggle sw on front Protect the tank with cardboard around three sides tied and taped in place before removing the prea. ch1 and ch 2 are totally different R25 is 47K//15K Maybe different Q12 , replacement is BC107 ch2 i/p tip is R, Bk sleeve, fixed contact W, moving P R40 3K2, R43 680R ch1 compressor sw R is common both sw, sw is c/o ch1 i/p sleeve Be, tip R, fixed contact P and other is Gy ch1 Rs and Qs R11 1K5, Q7 BF2450 ? Q10 part read as BC307505 Din socket Signal Be, R,W,Gy,Pk,W,Be 86V, 73.9V on caps TO5 54,0,0.48 Q1 .78, 0, .21V TO3 x2 //54.5, .48, 0// -54, -.3, 0 All mid controls ch 1 1V 400Hz in 50mV over 8R, 180mV with compressor off ch2 9.7V out with 10mV in , same with sound sw ip .54 op in normal ip Hiwatt , see Sound City for schemas perhaps Hiwatt AP CP103 ,2005 valve amp (and Hiwatt L. 100W, 1970) Blown mains fuse and owner thinks he replaced the HT and mains ones after initial failure. Amp failed in tune 5 into a gig , playing loud but normal for this amp (does "The Who" front label make it louder?) and fuse/s blew. Next day, he has a 1970 Hiwatt L 100W Mark 4 ? M41.. serial number anyway, and according to the owner very rare, this one should be ok when it gets 4 EL34 valves again. One of the 2005 EL34, the getter was white so he threw it out , unfortunately . I'm out of contact with him for a couple of days but looks as though the other of one of the side pair was partially white and kept this one same make and appearance as the others in the amp, now mixed in with his box of untested valves. I went to test that part failed one yesterday and over a couple of days it had turned fully white, must have been a very tiny leak/self-stopped, handling was enough to make it open up a bit Anyway in the end he robbed 2 EL34 from the working vintage one and still blew fuse/s. All Rs look and measure ok in the PA section. Powered up with 70 percent mains , 155V, with no output valves, only prea ones , and voltages seem right for that mains including bias voltage,303V and 310V on main caps, 238 & 183V on prea cap and -25.3V on bias electro Tx resistances seem normal. mains TX 4.1R primary o/p primary 14R. 10.6R This part white EL34 , 2/3 white , 1/3 mirror Cs getter, blown heater. The vertical rod electrically attached to p1 , G3 , but physically on the other side of the valve electrically connected by the top "halo", electrode is discoloured to blue compared to the other valves. No obvious cracks , I suppose deliberately breaking it will confirm was still functional getter. But something coming off the rod reacting with the getter while hot and not fully converted to a white form ? Won't be testing them and his other "spares" until tomorrow. One 8 pin black socket (marked Made in Italy , EE or maybe EF ?) is discoloured to dusty grey appearance around pins 2,3 and 6, 6? no pin in that one ?. Trying a 2.2mm drill shank (not the cutting end) it is close sliding fit to the old amp socket pins but slack sliding fit for the 2005 one Measured a few EL34 pin diameters, p1 and 8 2.22, 2.31 mm 2.26,2.30 2.18,2.33 2.26,2.30 EL34 from the 1970 amp 2,41,2.41 mm 2.40, 2.46 so suspect contacts in the sockets? and loss of bias voltage ? No one seems to know why the HT fuse is specified as 3A , same as the mains fuse. Replaced with 1.6A (T) , no blowing through numerous heavy throughput testing since. Should protect the mains Tx from being stressed unnecessarily. Retaining springs for the new version , not considered necessary in the the old one The Italian sockets are maybe marked EE, anyway socket pins are now strong sliding fit to 2.2mm drill shank. Curvey Es like the E of the compliance CE controlle european mark, maker name not found Googling The 1970 amp is marked Sound City "one hundred" on the gold fascia panel. Suspiciously small 63V 100uF bias cap replaced with 100V one in the 2005 amp. O/p Tx tests good balanced with reverse feed AF sig gen. Anyway with valve testing can be pretty sure of the "etiology" . Both these amps are stored in the same unheated warehouse, the newer amp looks far worse from internal corrosion, than the 1970 one. Poor socket pins and corrossion on the valve pins lead to loss of bias. Then owner robs a pair of valves from the good amp , but one of those valves has a broken polarising nib. Tracing back to my markings on receipt this valve was rotated one position out in the base, the one position that connects anode to cathode via the heater. The old valve pins showed no corrossion but the recent JJ ones had bad grey dust corrossion , leaving large grey deposits on cosmetic nail sanding boards. One valve tested on my Avo as no heater and took a lot of abraiding to the pins to get the heater current through. Another one tested as no gain until I repeated the sanding. The JJ valves had no date mark just an E in a cartouche. And marking N5LN5 datecode for 2005 ? I don't think the pin infil is PbF, but has the bright tin tinning of the pin surface turned to tinpest? - those grey patches were certainly insulating to 30M , DVM anyway. As a puzzle for anyone with the inclination. If the valve with the broken nib was placed in the socket with perhaps overheating marks in the bakelite of pins 2,3 and 6 what orientation would lead to serious overheating at those pins? The heater chain on these amps uses "dummy" socket pin 6 as a resistor tag from HT2 supply, EL34 are NC and usually NP for pin 6 sig gen reverse test of o/p Tx 1V 100Hz in , 5.3 / 5.31V out , DVM ac monitoring 1V 1K, 5.23/ 5.23 0.8V 10K, 7.26/ 7.27 V ac Bias -36.1V 40mV , 400 Hz in , all controls mid, 3.2V ac over 8R in 8R setting, bias going to -35.8V for 1 second with something like 25V ac over 8R Normal use bias dropping over 10 minutes to -36.6V HT capacitor balancing Rs , necessity ? Well I call them HT balancing Rs anyway, in valve amps. Where 2 HV caps are used in series to avoid using extra high voltage single caps. I always thought they needed 100K to 200K across each to balance out likelihood of midpoint voltage drifting up or down and exceeding the rating of one cap of the pair. Hiwatt AP CP103 ,2005 bouncing back blowing mains fuse , different set of output bottles from before. Worked for about 6 hours in total and over an hour before problem re-emerged. Amp lost sound fading without distortion, owner turned round in time to see the mains neon fail , ie after sound failure. This amp does not have balancing Rs , unlike its 1970s versions. I will add a couple of 220K/1W but anything else to ponder? These amps always seem to have had 3A mains fuses and 3A HT fuses for some odd reason - anyone know why? so the mains fuse sees more current than the HT fuse in normal use, same in abnormal sistuations? I thought about putting a telltale 2A fuseholder in line specifically with the caps and then thought better of it. A high voltage in the output Tx whan a fuse blows could induce very high voltages across windings but loosing the smoothing could mean an even higher peak voltage if the HT or Mains fuse should blow. Switches, wiring and fuses seem ok I dummy load test at 8 ohms and this amp is used at 16 ohms. When I set it for 8R no sound from the attenuated quality-monitor speaker. Seems ok in the 16R setting but perhaps when warmed from current over an hour goes open. That event at more than half full output would presumably blow a fuse if not an o/p transformer. These rotary sw are rivetted in , the 1970 version were sockets and double pin jumper selector type. 2 balancing Rs added . If it bounces back again then I think I will try a tell-tale in line with the main caps of a 1.6 amp fuse in parallel with vitreous 1R 10W . Difficult to gauge what values so that the fuse will blow in aberrant condition but not burn out the R if either mains or HT fuse holds and not blow in normal seitch on and use. The minor HTs supply is more straightforward , for such a telltale, as tempered by 100R dropper anyway and cladding of that vitreous looks as new Before adding the balancing R in the first 10 minutes the difference between the 2 caps voltage went from 25V to 35V and still increasing 1V / min or so before I decided that was evidence enough for some balancing. The 4/8/16R switch is made by SWP with logo of a linearised S in a rectangle. I would not want to rely on them for their supposed 250V/8A rating. The fixed contacts are just punched holes in the tinplated terminals and the moving contact, just a dome, path has 4 crude sprung surface contacts along the way I've just realised the mains voltage selector is the same make and design just different markings. That too is unreliable I now find concentrating on it, so now permanently wired for 240V , no bad thing, in case someone mistakes this selector for changing oputput for different cabs and in the UK. At least 1970s and earlier loop-thru-tag and solder assembly has gone by the board by 2005. Workman-like make of valve/tube sockets? That last more than 5 years before the gap in the socket pin opens up enough to break contact on the grid pin? octal EL34 type valves seem to have pins about 2.2/2.3 mm diameter. Failing socket pins , measured cold , a gap in the Y as large as 2.1mm. Luckily I've found a NOS McMurdo , British made socket that I will rob 4 of the pins from, for the 4 grids, as physically compatible in the base matrix. These unused ones measure 1.7/1.8mm in the active part of the Y gap. The failed ones from 2007 have reduced metal in the region where its required , the 2 prongs , except for a swelling at the contact point , measure in cross-section .7x.9mm down to the 2to1 middle of the pin . The older ones measure .55 x 1.4mm , the 1.4mm dimension in the sense that you want it , for long-term/hot-cold cycling strength. Any modern makes have engineering drawings disclosing these pin dimensions ? has the metal composition changed/ trade secret formulation lost? A sustainable source of robust sockets? Or even a source of pins of part spiral type perhaps , scaled up to 2mm of turned pin socket type say or even scaled up QM. I've only once come across bent pins on octal valves (owner bent them for easier access) . Just to replace the grid pins of modern sockets, if not the remainder. What else uses 2 to2.2mm size pins these days that has mating sockets? all the octal relay bases I've laying around have the simple Y fork type of pin and they may not be suitable for high temperature use. I did find some more NOS octal valve bases mixed in with them though. Replaced all 4 grid pins with the robbed beefier McMurdo pins Hiwatt Hi Gain 100, RoHS PbF, 2007 HW100 PW Federal on power Tx All 8 nuts fo rthe laminations of both Tx needed tightening and lock nuts addesd where possible and laqcuuer on the others Blown mains fuse, cracked through the ceramic and sand and blackened internal surface. Someone had replaced the 1A HT fuse with 3.1A at some point, which was ok. Someone had managed to strip the internal "screening" card from the staples holding it the cab base. Metal side to the inside, only the vaguest of plastic sheet insulation over it and could have been touching anything. No tag for an earth point/wire that I can see anyway, so that will not be going back inside. All logo/printing of each valve looks balanced thermal degradation (slight) but these Electro Harmonix all dated 0611 have flattened domes at the getter end. There is a recessed rough dimple in each of these , all off centre so unlikely at manufacture, signs of overheating? I,ve not seen these rather raggedy dimples before but I cannot believe the dimples would be so remarkably similar if the flat part of the tube was heated enough to start collapsing inwards (valves with base at bottom , ie not inverted orientation in use). Valve bases look normal, no colourations or discoloured valve Rs inside etc . No EL34 tested yet but the first valve I remove, the forked contact for grid pin 5 takes a 2.5mm drill shank inserted but touches a 2.55mm one. Previous Hiwatt, different model, stopped bouncing back after I replaced all the p5 forks with proper 30 yearold NOS ones . That one had forks with about 2.2/2.3mm forks that were suspect. That Hiwatt had wired in sockets but this is pcb type, so how to remove individual pins without removing whole sockets? Replacing complete 2007 sockets with 2013 ones seems a hiding to nothing. For good measure RoHS/PbF stickers aplenty. Owner queries whether it is due to being borrowed by a wannabe bass guitarist who uses extra mass per unit length strings on ordinary electric guitar, for some musical style purpose. Replace the fuse and the amp works fine, which doesn't help of course. The insertion / pull force of the EL34s is far too low, from experience, what force in KN that is I don't know Extraction only fingers of one hand , no wiggling required. Insertion force 3 to 4Kg far lower than usual. C frame around and under amp connected to a spring balance and a block of expanded polystyrene , off amp deformed with impressions to take top of C and top of valve. All 8 laminations bolts for the 2 Tx are loose to the point of nuts soon to be dropping off for 2 of the mains TX bolts. One of the seriously cruddy output fuses, with LED indicators, has highly suspect contact where the end cap quarter-turns in, so yet again having to replace these pcb mount fuse holders Looks like a matter of desoldering the heater chain wires and then hot air gun to the pcb under each socket while pulling the socket , to remove them. Seems odd to have a fuse in the AC to the bias supply Next time I have to desolder double sided large-mass PbF soldered valve bases , I will attack as the only time I've done lead-pipe soldering and use 2 hot air guns, one heating the base and one on the other usual side of the pcb. As large mass of solder requires a lot of heat to remove and the non-heatsinked central area of each valve will charr the pcb polyester so mark the pcb elsewhere with V3,V1,V2,V4. The heater wires have holes in the pcb to take the wires , so more solder and heat hungry to remove , cover heat damaged insulation with heat shrink before reassembling or replace These white no name porcelain bases have a form of pin I've not seen before, Google images did not show them , the distinctive feature is the pins are angled relative to radius and have joggles underneath so large footprint for takin solder on both sides of the pcb, this means that the through base part of the pin in angled and then Z joggled. If you view into the holes that take the valve pins , you can see the pins have joggles to them in a circumferential sense. Not the fairly common pip joggle inwards towards the valve pin at the point of contact but off the flat face of the pin , like mini humps. What that means is that instead of the valve pin forcing the forks apart, the 2 parts of the fork can slightly rotate out of diametrical alignment and so just a touching contact, not full mechanical contact I think the pin material is thick enough and the forks are not splaying apart , the usual dodgey contact failure mechanism but a slight torsional twist instead. Perhaps removal of p5 at least and squashing out the 2 humps is all that is required. The flimsy no name pcb 20mm fuseholders have a type number PTF 50 on them These joggled pins would probably have worked if the slots in the ceramic bases were a mm thinner so the metal forks could not twist/splay along their length. So an in-situ workaround would be formed metal forks pushed into the p2,5,7 slots to close up the freedom to move . Small brass solder tags 12.5mm , 6mm ring x .5mm thick. Grind into a fork and reduce the spine so overal length 8mm, and a 2.5mm drill will pass into the fork . Pushed into the socket pin slots with small flat blade , if difficult one side , swap to the other, well lodged in that interior area , held in by the hump joggles and the bend of the pin at the other end. With a spare valve check for good continuity in each base before resoldering. Neon is straight off the mains before sw 240V setting to the Arrow , not the more apparent knotch for scewdriver blade access, blown . 4 interior fuses ok. Replace the mains fuse and the amp runs full mains ok mains Tx 2.5R primary Waggling the sp ohmage selector makes no difference to readings over 1/4 in jack in o/p 4R , 1.4R 8R, 1.2R 16R, .5R PTF 50 on them These joggled pins would probably have worked if the slots in the ceramic bases were a mm thinner so the metal forks could not twist/splay along their length. So an in-situ workaround would probably be formed metal forks pushed into the p2,5,7 slots to close up the freedom to move 6L6 / EL34 valve bases for double sided soldering? Google images found none. Instead of pins in a ring of <>18mm diameter , they are on a <>27mm diameter so that the top side of the pin, lays outside the porcelain/matrix of the base, so can take soldering on both sides of the pcb. The socket pins have a joggle to them , to accomplish this UK supplier that is, I can find USA source on Google images with tube instead of valve search term I've had to fudge the 2,5,and 7 pins, stopping htem from twisting, with 0.5mm inserts. I'd have rather found some replacement sockets without the design flaw but owner wants his amp back. is a USA source and maybe a different design to the problematic ones used by Hiwatt . Need an underneath view to see if the pins are canted, but an engineering drawing to show if there are the problematic "humps" on the forks of the pins, would be more definitive On test buzz for o/p tx and no sp noise, I'd failed to reconnect sp o/p wires -44V on grid of each EL34 at mid setting -34V , 1 amp mains draw so adjusted back to -44V until new set of valves in place When making valve base inserts from small brass solder tags, cut into the ring that takes the valve pins, so square and not round, or will foul on the valve pins. This time without the enlarged holes, some silicone rubber with 8 holes puncehed in each to take up the gap between valve and base 1970 Hiwatt L 100W, 1970 mains Tx TG9743 and G988(6?) o/p Tx TG9375, G9909 main red caps CCL curley script , philips blue electros & cement cased polyester Red cap marked Mar 1970, CCL 100uF,70V Sprague 7001 datecode on 32uF, 450V o/p Tx 19.9R/17.5R sig gen reverse test of o/p Tx 1V 100Hz in , 5.41 / 5.41V out , DVM ac monitoring 1V 1K, 5.45/ 5.41 0.8V 10K, 7.53/ 7.51 V ac Testing with mid controls , 400Hz 50mV in , .25V over 8R Outermost outpus for single speaker use only HK Actor AT 112A , 2004 amp much the same as LUCAS 600 They have an otherwise original assembly method of the final contact to the pins of TO3 power transistors by 2 zero ohm "resistor" links, so 2 current paths to the pcb traces. Looks as though repaired 2 years ago, 2007,in UK, with (see logo thread ) with MJ11015/16 power Darlingtons that I suspected could be pirates as could not find logo. 2 of the TO3 devices shorted C-E on one side of the "H" 1 of those 2 are original colour but other three have a dirty brown/grey colouration of cap. I cannot figure out the failure mechanism. Will have to remove the other good pair to check under and will heatsink the 0R links while doing so. I doubt I disrupted the pcb solder when desoldering the B & E pins with the failed ones. Amp seems 2004 but replacement devices of matching dates on each pair of 2006 and 2007, looks well enough done repair, he would have seen any associated duff solder points in the process, surely. I don't like the closeness of the +/- live vanes of the h/s on a board that can easily flex with heat. From AD "Whenever I get one, I always remove the other pair of transistors as well, clean down their heatsinks, and re-paste them, not forgetting the flatpak transistor that's in contact with the underside of one heatsink on each channel. The manufacturers recommend that when the outputs are replaced, two of the BC546Bs nearby are replaced as well (T7 / 8 on one channel, 10 / 11 on the other). Check also C3 and C21 to make sure that they are not bulging. Other than this, these amps are very well behaved, and new outputs and fuses will, in 99.9% of cases, effect a complete cure. Note, however, that they have proper differential inputs, so are not that easy to drive correctly, unless you have a proper balanced XLR source, and that they don't like earthed test equipment connected to their outputs / inputs simultaneously. I usually hook a completely isolated speaker to them for final check, as the music shop which sends these to me for repair, often remove the amp chassis from the cab, to ease the transport, and save me having to strip it all out. He now tells customers when they collect the repaired unit, that they should brush out the air vents at three monthly intervals." Another hint- it is easy to accidentally short the solder tags the big diodes are soldered to, to the zero ohm links as you tighten the nuts I see no circuitwise reason for those repeated cap failures. The Darlington heatsinks are elevated off the pcb (trackside) with spacers and although the minor component side of the pa pcb is un-fanned I would not have thought pcb and working caps would get to 85 deg C Will make airflow mods and RTV-stick non-resettable thermochromic dots around various items , for if it bounces back. no room for that 100V size, unless put on track side of the pcb . As it happens space there and as the temp sensing TO220 s and fan air flow/temp sensor that side already I will solder replacements on that side I think both of those caps are bulging, I had not noticed up to now. I will replace those and the TO92s. A tip in reply for these and other apparatus with that grey interconnect ribbon. Before removing any such boards I run some hot-melt glue down the join of the cables at and to the board. So any bending, you have to do, is then only in the cable run which consists of multistrand but soldered wire, so will easily break where not supported by the grey plastic sheathing, ie at the ends, where it otherwise would choose to bend. The sort of wide pitched grey ribbon that has end stripped and conductors soldered directly to pcb, rather than headers I would have thought the ducted air design was about ideal for a given fan size, but I will bend inwards the outer fingers between the +/- dc carrying adjascent heatsinks. Perhaps the airstream takes the path of least resistance and does not pass through the 44 vane version of this type staggered fingers of those square format heatsinks and goes around outside instead. Perhaps bending inwards all 20 internal run fingers of each h/s would be a sensible mod, less vortexing/blocking, more open, would make less of a dust trap as well The good pair had good solder points under. All white goo was in oily state, One of those electros was o/c the other high ESR and both had more obvious bulge at the lead end This sort of 4mm wide double wall, staggered finger design, is for convection not passage of air through. Walls of 4mm gap blocked by 4mm finger repeated four times each side of the fan (2 h/s in line each side) is pretty effective wind break. Then 2 "gaps down the sides of 3mm wide x 35mm high and 70 mm long is similarly "resistive". Most cooling would be the 2 outer edges of 12 only of the 44 vanes each h/s where there is unobstructed passage outside the heatsinks and out to the surrounding duct 20 degrees is about the most or you block off access to the TO3s. Maybe only tinkering at the heat build up problem. Most air must go through the 25mm or so wide gap in the ps direction (over the tips of the vanes), rather than the 2 off 5mm gaps to the duct let alone through all those vanes. I would have thought there should be some shuttering to block off most of that large gap along the ps side , to force most air round and through the heatsinks. They were assembled with enough white goo to keep a goth happy for a week. So much that she filled the B & E holes so pins pushed through it, not cleaned off, and some white goo actually under the solder joints (not actually failures there). Those failed caps 47uF, 63V - in similar HK amp they were rated 40V 47uF , what is the problem in that area of the circuit? If make is relevant these blown caps, 2 types so I don't know which is original, both dark and light blue 47uF , 63V SG and logo of an eye, type? R4D 85deg C (M) probably original one as amp is 2004 and previous repair (if only 1) 2007 47uF, 63V YAGEO 08/03 (date Aug 2003? ) SK85 deg C This fan is outwards flow 4,000 sq mm of purpose built inlet holes and 3,300 sq mm through fan vent I would have thought was quite adequate if the air was directed over the heatsinks and not wind-breaked. This one permanent mounted high up away from floor dust. Compared with Laney CD850 , totally inadequate constriction on outlet over fan . 3 of those I've cut away the "vent" holes over the fan, fared off and covered with a wire grille and they've not bounced back (each was cutting out thermally after extended but normal use) As the Laney original design 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 , ridiculous aerodynamics By comparison, the main disadvantage of having fans blowing inwards is all internal stuff gets heated up to some intermediary temperature, between ambient and heatsink temp. Placed a partial baffle on the larger gap side of the ps board to force air more over the heatsinks rather than around Partialy locked off the open end , leaving cables and sleeves as adequate blocking at the other end, and bent inwards the inner lines of vanes on the heatsinks Initial powering with replaced darlingtons, 30V mains , taking .2 amp and low DC. C-B short on 11016 power diode tag touching base 0 ohm resistor, I had been warned about this but still fell for it. Bad solder on BD238 causing distortion 107/240 V mains then +/-21.5V. Relay clicks over at 26V half mains then rails +/- 27V and collectors of Darlingtons -27, -7.7V dut to bad main rail fuseholders. Speaker return to ground as high + low speaker terminals on bridged 1V in .437 satellite, .467V full , 400Hz 1V in .362,.477 for 150 Hz Umbilical 0,-15V,15V I/p at ground and pin furthest from the gain pot, sig gen 400 Hz 0.1V , gain at 1/2, umbilical 0.047V Fan draws air out but masked off at the heatsinks for this test and glass thermometer in thermal contact to both h/s 8 ohm on high power amp end .5V 400Hz in 5.9V over 8 ohm, 10 minutes to raise 42 deg C over ambient 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. Hughes & Kettner Attax 80 Splutters then fades , over half a sec, 10 to 20 minuts after start, any output level. In passing this amp seems to be prone to mains bourn flourescent light started EMI Tank red to front 196R, 27R y Sp 6.0R Rockdriver 121216 PA 2 x MJ4035, 081 PREA MC1458, MC14053, 2x 082, 2x 072 , 5532 Tx 12.8R// 1.2R at fuses 3 fibre washers on each 1/4 inso Bad return so bypass sw. Also replaced phones so as ground sw takes speaker current. 47uF 15V +560R feedback path to amp monitoring current through .15R (like H&K Vortex amp) Other R 22R 22W, 470R 1W, 180R 2W , 2x 1K2 , 2x 680R 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 Hughes & Kettner Attax 80, 1994 intermittant loss of power 10 to 20 minutes into use Replace return and phones sockets Umbilical 13/5V,0,0,15.4,-15.8,0,0,0,0,0,0,0 .1V 400Hz in ,1.6V over 8R all sw out and pots at 1/2 +/- 45.2V on TO3 8R load and .01V 400Hz in 42.4V and 45.3V over 180R Tr1 7.1,0,0 dc Tr2 .6,.02,42 Tr3 .6 , .005, 42 Tr4 42.5,2.4,42 Tr6 .8,.035,.03 Tr7 .7, .003, .003 Ibanez Maxon AD1301A , BB delay line, 1981 7815, MN3005, MN3101, 3x 4558, NE570 Bad 1.4 sockets, loose LED bad Alps 110F lever switch corroded replaced DIl socket with turned pin Ground connected to chassis at 7815 Replaced socket with wired in socket , open out hole and locate with hotmelt through nearby chassis hole. Because had to cut down width of plastic bush nut for clearance over front subcover and releive under the cover with countersink tool to take larger diameter. 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. Jensen 12 inch speaker attempt to rescue About 50 years old. Looks as though the card of the cone hase weakened with age, probably like the paper of books goes brown and crumbly over time. Looks as though the central cone area probably has failed to resist the returning force of the periphery and the spider and has buckled torsionally but not split in that inner zone ,one or so inches, from the voice coil join and radially out. This is a 12 inch Jensen speaker of about 1960. I suspect the periphery corrugations that should flex, had hardened up over the decades. Owner not overdrive abusing , I removed the central dome to check how much rubbing there was, no obvious scoring but did brush in some silicone oil. The VC showed through the gap in the former , as the original unusual green enamelling (not copper carbonate), looked fine. I covered this central area with a silicone bakeware cupcake mould and blasted the worst cockled areas with hot air on a low setting and pushed back wirth a spoon. In the end perhaps 50 percent of the original cockling. Then some spray adhesive in that cockled area Next time I may try hotter temp or try chemical to soften the card , water? diluted paint stripper? a small test patch initially whatever chosen. I think next time it would be a hotter temp of hot air and a matching cone of wood as a former , pushed in place, while cooling. There was some small cracks in the cone near the outer edge, 1mm hotmelt string "soldered" in those. After all that, here was still some very slight rubbing at the core, flexing the cone in by hand, perhaps the VC former needs remoulding as well, but it seems to work well enough to reduced power levels without distortion. Do the electromagnetic forces , form the former into more of a circle during powering? 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, 2 colour contrasting triple ply plastic sheet ,used for sign making with a pantograph engraver, traffolyte . 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. Tapco Juice J 2500 slave amp, 2007 One ch down but nothing visibly or rhinally amiss inside. How do American repairers get on with PbF boards, not marked as PbF. Is there an overlay codification meaning PbF or LF ? Has anyone collated together what USA makers + models for what 21C years definitely had PbF or definitely had leaded solder? Or putting it another way , what is the probability of any China manufacturer using leaded solder in 2001/ .../2007/ ... ? This amp made in China in 2007, for USA, exported to UK. Balance of probabilities from appearance, indentation test etc is probably PbF. Yet again faced with repairing a "fully working" but intermittant failure PbF amp However much tugging and twisting on input and output and pot boards cannot get either channel to fail, as user contact there, most likely failure areas. Closely inspecting all boards - no bad-contact solder found. So far powering to 75 percent mains, noting some mid-amp signal AC and DCs , as nothing useful out there on this amp. Before upping the mains (may of course cause a protect failure in one ch from that) . And before seriously attacking the main amps with engraver tool and nylon bolt as tip , monitoring large dummy loads with attenuated phones, to try and make a failure. On the pcb logo So from the E number E148158 RUIHUA PRINTED CIRCUIT BOARD CO FUZHOU, FUJIAN, CHINA Then pcb type number under the E number probably PbF , of course being USA , no mention, resoldering indicated PbF also. Comes apart easier than it looks, not one large board, 2 sparated pcb and heatsinks. Still nothing seen amiss so presumably false protection, at least no microcontroller seen. Plenty of SM under the pcbs but analogue seemingly Wanging everything with engraving tool + nylon bolt eventually elucidated. Loss of ch 2 , no prob on its i/p board, due to bad mono/stereo/bridge slide sw on the ch1 i/p board. Unusual DC rails for the SMD opamps , will go on my tips files for anyone else confused by this. One operates from -113V and -101V supplies and the other 40V and 55V, same for both ch A right pain to desolder, double sided thin board, thin traces, tiny pads , plated thru holes and PbF solder. 19 inch rack amp but with unnecessary miniature complex asymmetric switch impossible to find replacement for, 4 pole,3 way, but only 8 of the 16 pins used here. "re-soldered" with copious flux before hot-air desoldering because of extra PbF temp . Not contacts corrossion it would seem. I suspect sloppy phosphor bronze contact carrier/slider in outer metal shell, will rebuild with 0.5mm x 3mm hard PTFE strip padding out one side to stop it flopping about, and cleaning contacts. Maker YSC logo and also DC stamped on the outer. There is a potential safety issue with these amps. On reassembly make sure the mains switch crimp connectors are pointed downwards, easy to have bent them up to nearer normal straight rearwards, in moving wires and boards about. If straight out , then the plastic of the crimp will get squashed into the edge of the pcb with nearest track just 1mm away from mains connection. 4x 2SD1943, 2SC5200 Temp sensors measured in cct 18,6R ,36.9R, at 15 deg C All Tr DVM diode test from bases, Vbe and 22R ch2 U270 /271 LM311 underside of pcb ch1 also JRC1370D ,U2 under All TOP66 C to sp- sp+ to C221 main rail capand side of C222 ? main rail cap Remove 4 screws to both h/s under chassis Remove rear fan and duct, refit last no star washers under any pcb mounting screws remove ch2 amp , nearest Tx Then remove ch1 On reassembly of casing , 3 csk screws go to front aluminium panel. ch1 4x 8k2, 2x5k1, 22r, 2x 5r6, 2x 1r5, 2x 12r, 22,2x 12r, 0.056r, 3x 2k2, 8x 5W R2 Crowbar V ref are 2 back to back 2N5064 and WJ71 printed, 3 pin TO92 to the BT... triac U101 + supply via D101 , 820R sm, D107 to MJE15032G TO220 8A, 250V pass tr on h/s Removed i/p boards to check connections and loose when powering up with loose amps with insulation sheets under, stout enough to not be punctuured by standoffs in place Stereo mode and 60 percent mains, clipping on both ch +/-63V, +/-31V 180V mains , no fan 75 percent mains low fan 1/9V on front fan , good output +/-89V, +/-44V 2 second delay at sw on 20V on main rail , 20 seconds after sw off ch2 umbilical at 75% .5V in at 400Hz , 1/2 vol 2.5V o/p with no load R pin 5 clipped signal .64V, 8, 9 ,11,12 good at 2.5V ac DC 1 0, 2 14V, 3 0 , 4 -14.6, 5 16, 6 14.6, 7 0 , 8 -88V, 9 0, 10 -, 11 14V, 12 -14.6 Speaker outlets , hold back rear plates with screwdriver while aligning holes with a rod . From the user manual protections are DC offset, over temp, short cct, current limit Now at 100 percent mains Signal LED on with 0.1V 400Hzin, .52V over 8R at o/p .5V at U271 o/p .3V at U270 o/p h/s mounted supplies from end of h/s .1, 56, .7 and -.1, -56, -.7V umbilical -14, 14.1, 0, -14.7, 15.8, 14.7, .1, -113, -113, 0,0, 14.4, -148 dc ac 9 clipped sounding not scope observed,0,1.3,0,.18,0,0,.5,.5, .5,.5, 0 with .1V in 400Hz Red clip LED stays lit a long time after mains off, longer than mains LED Main rails 113,56, 0, -56, -113 unusual op amp supply regimes U271 -113, -101 and o/p at -113 U270 55,40 and o/p at 40V KAM LED lightcurtain , 2007? lightcurtain control box dropped and now no function. DC rails are right , not yet checked crystal and 555 sub cct function This has 4 channel output , 20V drive to an array of coloured LEDs. Assuming the NXP micro is defunct, and the owner does not use the DMX or mic input or even speed variation , just simple unvarying sequence 555 working. 16M Crystal osc working, but the only other pin with any activity is an unused external timing pin of divided clock f. Caps check ok, forcing a reset no change, as sprung pin socket for the NXP P89V51 micro added an intermediary 40pin turned pin socket. Any more last rites before consigning to the big dumpster? I've not checked the SN75176 DMX serial chip yet for perhaps latched o/p condition. I suppose using the variable 555 output to clock a 4 stage shift register and couple to the existing 4x TIP122 buffers would be sufficient for the owner's purposes rather than trying to find a suitable chrismass tree set Pulling the micro and trying a 4013 clocked by the 555 and feedback between the 2 flip-flops gives quite a pleasant pseudo-random sequencing to the 4 strings. Just have to hope it does not have a latch up state - I've forgotten how to determine that, clocked through a few hundred cycles without hickup. All Leds briefly flash at sw on. Checking wth a 12V battery , very low level LED light o/p Removed the 40 pin micro good randomness was due to an o/c input so settled on 4015 and a 4011 for hf oscillator for random data line input and inverter for the noise feed as HtoL transition on noise OR'd to the clocks of the 4015 and cross-link between the 2 SRs, taking o/p from every other o/p. Low at a 4K7 of the forces on the LED line different Rs probably due to different voltages required for the different colours drive per LED 4x TIP122,1W 51, 2x 68 , 2x 10R, 5V VR 18V wrt to DMX centre pin , otherwise 0V on the 5V reg tag p4 , blue in curtain to orange lead in con p5 , yellow in curtain, to Y in conn p1 white to red in curtain , joined to Y,Be,Gn and R supplies in curtain p2 R in conn to R in curtain p3 Bk in conn, SN75176 DMX serial 555 for speed variation NXP P87V51RB2FN buggered, Xtal drive ok and activity on p30 only LM358 op p1 & p7 Q1815 NH of 15V so divided 2R to 1R for the 2 CMOs driven from the 7805 white in line conn is +18V common. Standard LED clip ring glued to LED that had parted from the curtain. If use the existing 1K at 555 op then cut the trace to Q and take feed via 10nF to the clock and a diode from the noise divider and use spare sw on the rotary sw. 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 Kimbara "Ripper" bass guitar Copy of Gibson Ripper, pivkups 6K, "bypass choke" 3K loose in the space and twisted broken wiring . looked much like this 5x2mm Cu strip bent serpent like around all the controls, starting from 1/4 in so gnd contact and ending at sw housing. Mark where adjscent and cut a part slot in the copper to aid soldering to after abraiding back the lacquer ( large motor wire strip). Clicks on touching strings due to me failing to reconnect the earth wire to the fixed-end string clamp housing . No Al foil under fingerplate but left as found as no reported hum problems. hot melt glue spots to reinforce wire solder points after removing redundent gnd wires Korg also see Vox Korg Microkorg MKXL, 2009 PbF so redid usual suspects Impossible to use as duff volume control and coding pots having minds of their own KBd removal, 4x 20mm recessed screws only ELNA 0845 datecode 470uF 25V blown cap at power sw, but good ESR. Wired in replacement , space constraints All pots needed attention , migrating grease from bush area lifting the hair thin wiper metal ALPS 4C4 K20K top viewing of track 5K:15K semi log wiper1 , R1, R2, wiper 2, p1 p2 to p6 / p3 tp p5 , p4 ALPS AC502B 5K lin ALPS ZC502B ditto (difference dedent ?) BA05 large SM transistor BA15BCO One key out of kilter , higher. Broken plastic finger that touches the felt/ Doubled-up/large clothes peg to align with adjscent key , PTFE protection over felt and hotmelt blob replacing the brak. If now the key is too low, take up with a glued on pad of felt to the original. 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. Korg PSS 50 1984 , crackle o/p Needs about 10V to power up 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 Kustom KPS PM100, 2003 Bad click noise and no function 4sc under, 4sc rear h/s mark and undo 4 leads component side of ps/pa down STK404-100 , 7915, 100R droppers ok 2x 68R +/-37V to +26V and -28V via 136R, 136R neds more voltage dropping so replaced with higher W and higher R to reduce -28V to about -22V Kustom KPS PM300, 300W mixer amp , 2005 Intermittant failure after a few minutes, then dead the next time of powering up . Blue light, prea o/p and monitor at rear ok but no pa o/p internal or from rear ext feed. No relay click over heard soon after switch on Access remove 4 screws at top and one each side and rear in/out boards to remove whole ps/pa section and to protect it from bad handling remove the FX board. Leave all the rivets in place. The skirts around the speaker outlet 1/4 sockets were broken. Isolated from chassis so when refitting use some fibre washers instead to pack out. R-core type transformer pr 5.3R and 1.1R 41 to 41 and .4R for the blues 41,20.5,0,20.4,41 3.5A + 8V 1A, 130 deg C and 5 amp internal fuse dual power rails for switched stereo Sanyo Hybrid STK412-170 With no load , just quiescent amp , DC levels are 10 percent less than overlay figures eg 60V not 66V dc so more in agreement with the AC on the label and root 2 full wave rectified, also in relay off mode of the 1237 there is 60V on the IC o/p which is the rated maximum for the IC. I'm surprised no fan in this AC line is "AC" line, the rectified ac for the SIL upc1237HA, in data archives as PC1237. When testing this DC line with disconnected boards beware D-Gnd connected to chassis only through the painted steel around the rear 1/4 inch sockets and speaker GND connected to D-Gnd on ps board. Suspected protection IC or monitored lines, replaced the C1237 , 4.7uF and resoldered points and checked power lead lines. Accidently grounded the AC monitor line and mutes the relay with auto reset. When powered up ,opened up, then in working order and 1237 read as 0,0.01,0,1.88,0,.73,2.2,3.35 and normal 24V relay drive pa 14K NTC H/S thermistor (make surw in thermal contact on re-assembly) , Rs etc look hand placed and many touching one another and Zobel coils etc Undo pa section to view soldersides PA uses 2x 100R, 4x 4R7,1K8,2x 1K, 4x 0.1 5W 4x 4558, 2x CA3080 PS uses 100R, 8K2,2x 5R 5W one lead nearly touching diode lead, 2x 4K7 2x 7815, 7915,7805 +/-66V uses 10000uF, 80V and +/-33 4700uF, 50V electros Intermittant cutting out of an amp , something to do with the uPC1237HA protection IC. Number of control inputs (o/p DC fault sense etc) that takes o/p low of main speaker relay which clicks over. In fault mode this o/p goes to 60V via the relay, all quite normal and in spec but for a small SIL IC with 3.4V on the supply pin, a bit disconcerting. Incidently what does Vcc mean wnen an IC is rated for 60 volt Vcc (from the NEC datasheet) but 3.4V the recommended supply voltage Next time coming across similar fault I will change the 100uF ,3 second power-on-delay timer , temporarily, for 1 or 10uF as although the main fault would operate immediately it would take 3 seconds to reset making tracing infuriating as not immediate on/off. Changed the IC and caps around the IC and just about to change Rs around it although nothing has checked bad - still the problem persists. I decided to change the 4.7uF electrolytic (power off muting one) for the second time (most twizzle sensitive to inducing fault near this C) and this time the solder pad came away with the molten solder. Of course everything all nearby and elsewhere concerning soldering and pads looked fine and tested for continuity fine. Perfect ring of solder with a white pad (like overlay printing) showing under the solder blob , with the cap wire still in place passing through. Track , perfectly wide about 2mm, had failed in a neat circle around the pad. Only ever touching contact between track and solder pad or resonance vibration effect tearing in use ? bearing in min only a very small electro. Only 2V or 0V on this cap and less than 20mA , so I assume manufacturing fault. What led to the fault and what to visibly check for (if possible) with other pads before returning amp to owner ? The components looked hand populated despite 2005 manufacture, including resistors canted over and touching one another. A propbably related effect is the solder run reinforcement for current carrying along the main rails. There are bare sections with what loooks like oxidised dull brown copper instead and looks like fractured ends to the remaining solder. I found no loose bits of solder inside so probably had dropped away at manufacture, so passing final assembly inspection, all in all a bad job. Been exploring with a microscope. Not broken away pieces of beef-up overlain solder runs along the main rail traces, incomplete soldering in the first place, covered in the overall thin conformal coating, the bare copper going dark brown underneath in just 4 years. As for the failed C pad This pad had survived original soldering, my first desolder and resolder and came away with second desoldering leaving bare board where the pad was. I expected to see copper colour after scraping into the white circle but only silver colour of solder seen - no copper pad there ever? so thin it disolved ? when I desoldered/resoldered initially there was a normal pad of solder there the pa and ps share the same hs so I put the 2 caps on the track side of the board, mainly so easier to temporary change the timing 100uF to 1uF if necessary. the 4.7uF smooths the rectified ac for power-off sensing but with it intermittant contact , when that IC pin goes less than 0.7V in next mains cycle and all the following presumably, it triggered muting. Anyway second time of desoldering the small cap, the pad came away, with the usual few grams of force when blob molten. As a wired C , i desoldered with normal soldering iron. Diverse Devices,Southampton,England
Telephone number - the same number as it has been since 1988 but email is now the preferred method of contact so number deliberately not placed here.
I devote time each day to replying to emails.
(obscure/obsolete components,second hand test equipment, schematics etc) Postal: 66 Ivy Rd, St Denys, Southampton, Hampshire, England , SO17 2JN There is no point in contacting me about any of the above, the repair job may have been done 15 years ago . I cannot clarify or enlarge on any of the above.

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A reserve email account is diverse9(commercial at) Please make emails plain text only , no more than 5KByte or 500 words. Anyone sending larger texts or attachments such as digital signatures, pictures etc will have them automatically deleted on the server. I will be totally unaware of this - sorry, again blame the spammers.
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