My son purchased a Peavey Classic 50 guitar amp some years back from a fire sale at a local music store that was severely smoke damaged. It was to have been tossed out after their insurance settlement but he was able to pick it up for less than $100.
Long story short, we are now going to try to bring it back to life and I was wondering how to go about cleaning the circuit boards prior to troubleshooting. Anyone have any suggestions?
it doesn't appear there was any water damage, and it would seem as though the temperature it was exposed to never got above about 450-500 degrees F since the cover of the instruction manual stored in the back of the amp was just barely turning brown.
As far as the tubes go, are there any useful tests I can perform on them (besides continuity) using only a multi-meter? I have a friend who has access to a tube tester and I will be taking them to him, but I am trying to use this project to teach my son a few things about electronics and hopefully steer him into learning more.
Thanks for any and all help.
Len
Long story short, we are now going to try to bring it back to life and I was wondering how to go about cleaning the circuit boards prior to troubleshooting. Anyone have any suggestions?
it doesn't appear there was any water damage, and it would seem as though the temperature it was exposed to never got above about 450-500 degrees F since the cover of the instruction manual stored in the back of the amp was just barely turning brown.
As far as the tubes go, are there any useful tests I can perform on them (besides continuity) using only a multi-meter? I have a friend who has access to a tube tester and I will be taking them to him, but I am trying to use this project to teach my son a few things about electronics and hopefully steer him into learning more.
Thanks for any and all help.
Len
just how severe is the smoke damage? can you upload pic's?
if it's badly carbon fouled or sooty you'll have to disassemble it and clean it otherwise it might arc and catch fire!
in some cases cleaning with a damp sponge and mild dish soap on chassis and panel surfaces will suffice but on circuit boards i'd recommend you get a can or two of a decent non residue contact cleaner and an old toothbrush,paper towels,rags,maybe a cup of coffee...and have at 'er!
ps refresh my memory the Classic 50 is a combo isn't it? wondering about what the speakers are like(did the cones get affected by the heat)
if it's badly carbon fouled or sooty you'll have to disassemble it and clean it otherwise it might arc and catch fire!
in some cases cleaning with a damp sponge and mild dish soap on chassis and panel surfaces will suffice but on circuit boards i'd recommend you get a can or two of a decent non residue contact cleaner and an old toothbrush,paper towels,rags,maybe a cup of coffee...and have at 'er!
ps refresh my memory the Classic 50 is a combo isn't it? wondering about what the speakers are like(did the cones get affected by the heat)
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Isopropyl aclohol (rubbing alcohol) is great for cleaning electronics. It's likely cheaper than canned contact cleaner, and no risk of it having any sort of lubricants that will be left behind. Like turk said, tooth brushes, care and time. A well ventilated area and a fan to keep the fumes out of your face would be a good idea too.
Is it possible the insulating wire in the transformers might have melted through, causing shorts? Is there any way to check the transformers are in good shape and safe to use?
I also vote isopropyl alcohol for soot removal. I use a Qtip dipped in the stuff. The alcohol wets the board but evaporates away quickly.
Tubes were not probably affected much, but there is little you can test on them with a meter other than to see if the filament is open, which is unlikely.
A little stain from smoke probably won't hurt it, but if the boards are carboned up, they need cleaning. Otherwise, I;d fire it up and see what it does.
Tubes were not probably affected much, but there is little you can test on them with a meter other than to see if the filament is open, which is unlikely.
A little stain from smoke probably won't hurt it, but if the boards are carboned up, they need cleaning. Otherwise, I;d fire it up and see what it does.
Thanks for all the responses!
Turk182, Yes, this does have 2-12" diameter speakers. I think the actual model number is something like model 50-212. I think Peavey also makes a version with 4-10" speakers as well. As for pictures I'll try to get some uploaded this weekend.
Doozerdave, Will 70% isopropyl alcohol work or does it need to 100%? Will the small amount of water hurt?
Mikey R, I am hoping the shellac on the transformer wires didn't burn off. I hope I won't have to replace the output transformer! Does anyone know what the replacement output transformer costs? The Mercury Magnetics "upgrade" piece is all I've been able to find on the web. The price seems steep at $270. Is it worth it?
Enzo, Back when my son first got the amp he plugged it in and turned it on - blew the fuse right away.
It may be something simple though. I took a quick look at it tonight and I see there is a muffin fan in it that seems to be trashed. Does anyone a free source on the web for an accurate schematic? The one I found is dated March of 1993, and it doesn't show the power transformer or the fan.
Thank you all for your suggestions.
Len
Turk182, Yes, this does have 2-12" diameter speakers. I think the actual model number is something like model 50-212. I think Peavey also makes a version with 4-10" speakers as well. As for pictures I'll try to get some uploaded this weekend.
Doozerdave, Will 70% isopropyl alcohol work or does it need to 100%? Will the small amount of water hurt?
Mikey R, I am hoping the shellac on the transformer wires didn't burn off. I hope I won't have to replace the output transformer! Does anyone know what the replacement output transformer costs? The Mercury Magnetics "upgrade" piece is all I've been able to find on the web. The price seems steep at $270. Is it worth it?
Enzo, Back when my son first got the amp he plugged it in and turned it on - blew the fuse right away.
It may be something simple though. I took a quick look at it tonight and I see there is a muffin fan in it that seems to be trashed. Does anyone a free source on the web for an accurate schematic? The one I found is dated March of 1993, and it doesn't show the power transformer or the fan.
Thank you all for your suggestions.
Len
Well, I was doing some research on this recently, and I agree that it should be fine if you clean the board up, and the tubes should be fine, as smoke wouldn't affect them, and as long as your okay with the cab, it will be a great amp. SOME people actually remove the amps transformers in some amps such as flood amps or amps that were in mud slides and put them in a dishwasher... yikes, I wouldn't recommend this crazy act, but obviously the boards must be cleaned. You may have even gotten lucky and the boards are clean somehow, or maybe you are unlucky and the tube sockets arced over creating a carbon trace and need to be replaced. The transformers should be fine and can be checked for continuity or shorts with a multi-meter. Good luck with your project.
Last I checked, "pure" isopropyl was still dirt cheap, and only a few cents more than the wattery version. And while that 100% stuff does adsorb a tiny percent or two of moisture the moment it is opened, it leaves little or no residue of water behind. The 70% stuff will try to leave your board wet with water to some extent. I use it commercially here, and my 16oz bottle was opened 8-16-09 and is half left. Cost $1.58.
Buying a Mercury Mag transformer for this amp is like buying a racing exhaust system for your mom's car, when it just needs a new muffler. It will work fine, maybe even "better" but kinda overkill. At least to me. Peavey parts are reasonably priced.
Like ANY Peavey product, you can contact customer service at the factory and they will send the schematics to you. Here is a link to the schematic itself, but the factory file is cleaner looking, plus it will include the layout drawing and parts list.
http://www.webphix.com/schematic heaven/www.schematicheaven.com/newamps/peavey_classic50.pdf
The factory file includes the power tranny primary circuit. The secondary connections are inferred on the schematic, and are not drawn out anywhere. The primary circuit is trivial. Fan is parallel the transformer primary. Fan has a 700 ohm resistor in series. No part number on the fan, Peavey would source it to you by description ("Classic 50 fan"). Or read the fan label and source one yourself from Mouser or someplace. The dimensions are a standard size.
If it blows fuses, isolate the problem. First, look up "light bulb limiter", make one, and use it. If unsure of the transformers, first, disconnect the power tranny secondary wires from the boards. Please label them so you know where they go back. Power up the transformer only and see if it holds a fuse and makes AC volts. (With your limiter "blowing fuses" means lighting the bulb brightly) If the transformer itself blows fuses, it is bad, but if it works. then connect the secondary windings back to the boards one at a time to see which one has the fuse blowing effect.
Before connecting the high voltage wires, try disconnecting the output transformer primary. If the output tranny is shorted, this will eliminate it for testing. WHile the OT primary is unhooked, look on the power tube board right next to the fuse at the end. Are two diodes, CR6,CR5. If one of those shorts, it will blow fuses. Check.
Buying a Mercury Mag transformer for this amp is like buying a racing exhaust system for your mom's car, when it just needs a new muffler. It will work fine, maybe even "better" but kinda overkill. At least to me. Peavey parts are reasonably priced.
Like ANY Peavey product, you can contact customer service at the factory and they will send the schematics to you. Here is a link to the schematic itself, but the factory file is cleaner looking, plus it will include the layout drawing and parts list.
http://www.webphix.com/schematic heaven/www.schematicheaven.com/newamps/peavey_classic50.pdf
The factory file includes the power tranny primary circuit. The secondary connections are inferred on the schematic, and are not drawn out anywhere. The primary circuit is trivial. Fan is parallel the transformer primary. Fan has a 700 ohm resistor in series. No part number on the fan, Peavey would source it to you by description ("Classic 50 fan"). Or read the fan label and source one yourself from Mouser or someplace. The dimensions are a standard size.
If it blows fuses, isolate the problem. First, look up "light bulb limiter", make one, and use it. If unsure of the transformers, first, disconnect the power tranny secondary wires from the boards. Please label them so you know where they go back. Power up the transformer only and see if it holds a fuse and makes AC volts. (With your limiter "blowing fuses" means lighting the bulb brightly) If the transformer itself blows fuses, it is bad, but if it works. then connect the secondary windings back to the boards one at a time to see which one has the fuse blowing effect.
Before connecting the high voltage wires, try disconnecting the output transformer primary. If the output tranny is shorted, this will eliminate it for testing. WHile the OT primary is unhooked, look on the power tube board right next to the fuse at the end. Are two diodes, CR6,CR5. If one of those shorts, it will blow fuses. Check.
Finally got some time today to get some pictures. It looks like it might be in better shape than I first thought, though there appears to be considerable surface corrosion, especially on the pots.
Enzo, Thanks for the response. I was curious about using 70% isopropyl alcohol only because between my wife and daughter I have about 1/2 a gallon of it! I'll be getting some 100% this week and will also be contacting Peavey tomorrow to order the schematics. I did notice the wire colors from the output transformer does not match the one from Webpix.
This is after my son and a friend started cleaning/disassembling 4-5 years ago.
The internals don't seem too bad as far as smoke damage is concerned.
The green wire floating in the center of the picture looks to be the only broken wire I can readily find. It come from the output transformer - any suggestions as to where it is supposed to go? I THINK it goes to one of the output jacks but I'm not sure.
No worries though, this will not be seeing mains power for some time until I can get it cleaned up, have the schematics in hand, and I have some quality time to go through it properly.
Turk 182, The speaker seem to be in a functional condition; no rips or tears. With luck I can hook them up to one of my stereos later tonight or tomorrow night.
Thanks again for everyones suggestions.
Len
Enzo, Thanks for the response. I was curious about using 70% isopropyl alcohol only because between my wife and daughter I have about 1/2 a gallon of it! I'll be getting some 100% this week and will also be contacting Peavey tomorrow to order the schematics. I did notice the wire colors from the output transformer does not match the one from Webpix.
An externally hosted image should be here but it was not working when we last tested it.
This is after my son and a friend started cleaning/disassembling 4-5 years ago.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
The internals don't seem too bad as far as smoke damage is concerned.
An externally hosted image should be here but it was not working when we last tested it.
The green wire floating in the center of the picture looks to be the only broken wire I can readily find. It come from the output transformer - any suggestions as to where it is supposed to go? I THINK it goes to one of the output jacks but I'm not sure.
No worries though, this will not be seeing mains power for some time until I can get it cleaned up, have the schematics in hand, and I have some quality time to go through it properly.
Turk 182, The speaker seem to be in a functional condition; no rips or tears. With luck I can hook them up to one of my stereos later tonight or tomorrow night.
Thanks again for everyones suggestions.
Len
green wire looks to me like it has a piece of shrink tube on the end, and so is likely an unused 4 ohm tap on the output transformer.
This seems maybe overly obvious (did I miss something earlier), but if the amp was heated up THAT much, I'd expect ALL the electrolytics to be questionable, if not actually bad. They can't handle anything much beyond the boiling point of water, whereas tubes pretty much have to get hot enough to melt something before they're damaged. Leaky electrolytics in the power supply will blow the fuse. Leaky caps in cathode bias circuits will underbias the tubes and draw excessive current (POSSIBLY blowing the fuse if it's the power amp, but not good no matter what).
Hi all!
I have finally had some time to get some cleaning and inspection done though there is still plenty more to do.
I began by removing and cleaning the top, component side, of the power board which was barely coated with soot. Upon flipping it over here is what I found:
After about a half hour of scrubbing with isopropyl alcohol with a toothbrush and Q-tips here is the result. I am not done yet but thought I would show the first of the problems I found so far.
One trace on the right third of the board has been vaporized! It also seems as though the coating over the supply traces along the bottom of the board has melted away as well.
Can I repair this and have the amp work correctly or do I need to replace the board? If I repair it which would be the best way?
Right off, I can think of two ways to proceed; build up a solder bridge to reconnect the traces, or use a short section of wire connecting it to the closest wire/pad junctions on the trace. With either method should I attempt to reseal the exposed traces that appear to have melted away?
Thanks again for everyone's help.
Merry Christmas!
Len
I have finally had some time to get some cleaning and inspection done though there is still plenty more to do.
I began by removing and cleaning the top, component side, of the power board which was barely coated with soot. Upon flipping it over here is what I found:
An externally hosted image should be here but it was not working when we last tested it.
After about a half hour of scrubbing with isopropyl alcohol with a toothbrush and Q-tips here is the result. I am not done yet but thought I would show the first of the problems I found so far.
An externally hosted image should be here but it was not working when we last tested it.
One trace on the right third of the board has been vaporized! It also seems as though the coating over the supply traces along the bottom of the board has melted away as well.
Can I repair this and have the amp work correctly or do I need to replace the board? If I repair it which would be the best way?
Right off, I can think of two ways to proceed; build up a solder bridge to reconnect the traces, or use a short section of wire connecting it to the closest wire/pad junctions on the trace. With either method should I attempt to reseal the exposed traces that appear to have melted away?
Thanks again for everyone's help.
Merry Christmas!
Len
Rather than simply repair the vaporized trace, you might wonder what caused it to "poof". The repair might just poof again when you eventually power it up. You need a good schematic and know what you're looking at, to determine what might have caused the damage. Fire would have damaged adjacent traces as well I would think?
Wilade
i think you have an open trace to the heater supply and from the look of things it looks like the plate supply traces got hot.
it doesn't look unsalvageable it won't look pretty but wire jumpers are better than trying to flow solder across some of the large sections of missing foil!
before you power this chassis up i implore you google "dim bulb tester"and assemble one for your bench.
if you find yourself needing schematics or images of the board patterns PM me.
p.s. it appears most of the damage was due to the carbon fouling from the fire=conductive path from plate supply to the heater circuit.
i think you have an open trace to the heater supply and from the look of things it looks like the plate supply traces got hot.
it doesn't look unsalvageable it won't look pretty but wire jumpers are better than trying to flow solder across some of the large sections of missing foil!
before you power this chassis up i implore you google "dim bulb tester"and assemble one for your bench.
if you find yourself needing schematics or images of the board patterns PM me.
p.s. it appears most of the damage was due to the carbon fouling from the fire=conductive path from plate supply to the heater circuit.
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Turk 182,
Thanks for the reply!
My thoughts exactly on the carbon fouling, it's a huge mess! I now have cleaned the pre-amp board as well, which had an even heavier coating, I still have the main control board to remove and clean yet to do.
As for the dim bulb tester, I'll be building one this weekend. One question though; some of the ones I have seen online say to use a 100 watt bulb, I don't have one, can I wire 2-60 watt bulbs in series or will one 60 watt bulb be OK?
As for the wire to repair the output board; which side of the board should I put it? I have some 18-AWG, 600V wire rated at 150C that I'm planning to use. Will that be OK or is another type/size of wire better?
Incidentally, I did try out the speakers on the stereo down in the basement and they played static just fine so I'm hopeful. I didn't have an antenna attached to it yet and didn't have a CD to try. Maybe this weekend.
Thanks for your help.
Len
Thanks for the reply!
My thoughts exactly on the carbon fouling, it's a huge mess! I now have cleaned the pre-amp board as well, which had an even heavier coating, I still have the main control board to remove and clean yet to do.
As for the dim bulb tester, I'll be building one this weekend. One question though; some of the ones I have seen online say to use a 100 watt bulb, I don't have one, can I wire 2-60 watt bulbs in series or will one 60 watt bulb be OK?
As for the wire to repair the output board; which side of the board should I put it? I have some 18-AWG, 600V wire rated at 150C that I'm planning to use. Will that be OK or is another type/size of wire better?
Incidentally, I did try out the speakers on the stereo down in the basement and they played static just fine so I'm hopeful. I didn't have an antenna attached to it yet and didn't have a CD to try. Maybe this weekend.
Thanks for your help.
Len
good news about the speakers!
with respect to lamp wattage; i've used everything from 7 watt nite lite bulbs to 500w par lamps it's a choice made by making an educated guesstimate as to what the expected current draw will be to operate normally(that info i generally glean from the ratings that are usually listed on the device i'm testing)a 40 or 60 watt is the norm for me for initial testing.i'm lobbying to have the "dim bulb tester" changed to "homebrew ac current limiter" the lamp wattage determines the limit.
if you can find 16 gauge high temp insulation wire for your board "jumpering" that would be better!
with respect to lamp wattage; i've used everything from 7 watt nite lite bulbs to 500w par lamps it's a choice made by making an educated guesstimate as to what the expected current draw will be to operate normally(that info i generally glean from the ratings that are usually listed on the device i'm testing)a 40 or 60 watt is the norm for me for initial testing.i'm lobbying to have the "dim bulb tester" changed to "homebrew ac current limiter" the lamp wattage determines the limit.
if you can find 16 gauge high temp insulation wire for your board "jumpering" that would be better!
Happy New Year everyone!
The saga continues...
So, I built the dim bulb tester and due to my own ignorance (laziness?) as to exactly how to interpret the results, I went ahead and replaced the main fuse plugged it into the wall and turned the amp on, still without any of the tubes installed. The fan started right away and the pilot light lit brightly. I thought I was home free! Alas, after 10-15 seconds, the fuse just after the secondary (F2) blew with a flash.
I should mention that I have removed and cleaned all of the boards and terminals and cleaned both sides of as much soot as I could, paying particular attention to the spaces between components and pads/traces. I have also repaired the blown trace on the power amplifier board by soldering a wire between pads on the board. I also removed all traces of flux as well.
After cleaning I reinstalled all the boards back into the chassis but did not reinstall the tubes.
For my initial troubleshooting I have:
1. checked all of the transformers leads and both seem to be completely healthy, no shorted or open windings and continuity through the coils.
2. Checked resistance across the bridge and found 17.01M ohms across the input and 1.0 ohms across the output.
3. I checked the individual diodes in the bridge they all measured between 4.3-5.5 M ohms, and using the diode testing function all measured about 5-volts, but in both directions. I assume they should be measured out of the circuit to get an accurate measurement.
There still seems to be a dead short somewhere in the circuit. Any suggestions as to where to look next before I just start pulling parts and testing every piece?
Any guidance will be greatly appreciated.
Len
The saga continues...
So, I built the dim bulb tester and due to my own ignorance (laziness?) as to exactly how to interpret the results, I went ahead and replaced the main fuse plugged it into the wall and turned the amp on, still without any of the tubes installed. The fan started right away and the pilot light lit brightly. I thought I was home free! Alas, after 10-15 seconds, the fuse just after the secondary (F2) blew with a flash.
I should mention that I have removed and cleaned all of the boards and terminals and cleaned both sides of as much soot as I could, paying particular attention to the spaces between components and pads/traces. I have also repaired the blown trace on the power amplifier board by soldering a wire between pads on the board. I also removed all traces of flux as well.
After cleaning I reinstalled all the boards back into the chassis but did not reinstall the tubes.
For my initial troubleshooting I have:
1. checked all of the transformers leads and both seem to be completely healthy, no shorted or open windings and continuity through the coils.
2. Checked resistance across the bridge and found 17.01M ohms across the input and 1.0 ohms across the output.
3. I checked the individual diodes in the bridge they all measured between 4.3-5.5 M ohms, and using the diode testing function all measured about 5-volts, but in both directions. I assume they should be measured out of the circuit to get an accurate measurement.
There still seems to be a dead short somewhere in the circuit. Any suggestions as to where to look next before I just start pulling parts and testing every piece?
Any guidance will be greatly appreciated.
Len
if f2 blew you still have problems with the heater string in the pre-amp section.
was your limiting lamp lighting hard or what?
was your limiting lamp lighting hard or what?
Success!
I found and eliminated the short circuit! Apparently someone previously had removed a few jumpers and replaced them incorrectly.
The jumper going from the preamp board ground, J73, had been attached to, J57. This caused a dead short across the filter capacitor, C37. J57 is supposed to attach to the center tap of the output transformer primary.
With the jumpers now routed correctly, I re-ran the dim bulb test and it performed as expected, starting bright and dimming quickly. I replaced the tubes, one set at a time, and ran the bulb test each time. All appears to be working as expected. I then connected it directly to the power and let it run for about half an hour, all the tubes glowed as I would expect them to.
I hope to connect the speakers later today to see if there are any noises present that shouldn't be there.
Thanks for your help!
Len
I found and eliminated the short circuit! Apparently someone previously had removed a few jumpers and replaced them incorrectly.
The jumper going from the preamp board ground, J73, had been attached to, J57. This caused a dead short across the filter capacitor, C37. J57 is supposed to attach to the center tap of the output transformer primary.
With the jumpers now routed correctly, I re-ran the dim bulb test and it performed as expected, starting bright and dimming quickly. I replaced the tubes, one set at a time, and ran the bulb test each time. All appears to be working as expected. I then connected it directly to the power and let it run for about half an hour, all the tubes glowed as I would expect them to.
I hope to connect the speakers later today to see if there are any noises present that shouldn't be there.
Thanks for your help!
Len
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