Peavey 2.6C Question

[tonecat]

Hello,
Working on a Peavey 2.6C power amp. The owner hooked it up to a shorted speaker cable. When I turned it on, it tripped the breaker after making a loud humming sound for a second. I pulled the output transistors Q103, Q104, Q109, & Q110 (part # MJ-15015 and MJ-15016) and some are good and some are bad. Is it necessary to replace all of them together as a set and should I also replace the drivers Q100 & Q113 (part # MJE-243 and MJE-253)? Also, CR125 & C225, the SAC-187 triacs are suspect but I can't find a suitable replacement part from mouser. I tried the Peavey cross reference chart and it gave me 2N6436A as a replacement but they don't have that either. Any ideas? I was trying to avoid ordering parts from more than one place. Is there anything else I should look out for that might of got fried? One thing I did notice is the board looked like it got really hot around R141, R142, & R153 power resistors. One last question. Is it safe to test an amp without the power transistors in it just to see if the voltages are in spec without a load? I'm still learning with this solid state stuff. I attached a schematic but it isn't the best quality. Thank You for your help!!

PV 260 PV 2.6 schematic.pdf

[nosaj]

just got off phone with peavey for something else and asked the parts dept if they had the parts your looking for and they do have them in stock as of 8:24 central time.

18777328391 x 1386..
You can't find parts always try the parts dept. Peavey is very friendy never had a problem with sourcing anything from them .

jason

[tonecat]

Thanks for the reply. I will call them tomorrow and see if I can just get all the parts from them. I tested all the power transistors using this method:
With multimeter in diode mode, test each pair of leads both ways (six tests in total):

The base-emitter (BE) junction should behave like a diode and conduct one way only.
The base-collector (BC) junction should behave like a diode and conduct one way only.
The collector-emitter (CE) should not conduct either way.

I found two power transistors were bad. Is there any reason I need to replace all of them?? From my research, I don't think I need to. I don't think they are like a tube that can exhibit signs of wear? They either work or they don't? If someone could please lend their expertise on this, I maybe able to learn something and save some money at the same time. I also tested the drivers (5331 & 5332) the same way and two of them were bad also. I think since they are so cheap I will just replace all four of them and save the others for spares. If anyone could please give me some guidance on my other questions from my first post I would greatly appreciate it. The board got really hot around the two 700 ohm power resistors. Something must of been drawing a lot of current. Also, I don't know if it is safe to test without the power transistors in the amp. Never tried it before. I know you can check voltages in a tube amp without the power tubes. Just wondered if the same applies to transistors. Excuse my lack of knowledge. Just trying to learn as much as I can!! Thanks again!!

[Jazz P Bass]

There really is not an easy way to verify if a transitor will "work" if it passes the diode check.
I guess you could build a circuit to "test" each transistor under dynamic conditions.
Generally, in a catastrophic failure, it is safest to just replace them all, in an amp like this.
Along with the drivers.
Make sure that you check the low value ballast resistors.
They can go open when things go bad.
The bias transistor & it's associated components should also be checked.

[fredy2]

When restarting an amp, use the series light bulb in the power input to limit the current should there be other bad components. Use 150 or 200 watt lamp for larger amps.

[tonecat]

Thanks for the help guys!! I guess I kinda thought that I should replace all of them and the drivers too. I checked all the .33 ohm ballast resistors and they were all good. Already had thought of that. Now for my next issue. The board layout I have is different on the schematic. I contacted Peavey and they said that schematic was all they had on this amp. Some of the components are in different places. Could someone help me identify the bias transistor and which other components I should check and I will trace them down on the board itself? Also, is safe to power this amp on without the power transistors and the drivers in it to check other voltages? I have a Sencore Powerite I use when doing all my repair work so I can check current draw, etc. Thanks again for your help!!

[Jazz P Bass]

I would not turn on the amplifier unless everything was in place.
It really won't prove anything, unless you are just checking the power supplies.
If the output section has been gutted & replaced, why not install the new parts.
You have to static check everything in the output section.
You had a shorted failure.
It takes time & patience.
That way your confidence level will go up.
A working amp should not draw more than 50 watts from the mains, at idle.

[tonecat]

Thanks Jazz. I will wait until all the parts get here and I get them installed before I fire it up. I just want to make sure I don't fry any of the new parts if something else is still wrong with the amp. I thought maybe I could check the voltages at the base and collectors of the 5331 and 5332 drivers while they were out to see if they were in spec. Also, what do you mean by "static check the output section"? I think need to learn more about how this solid state stuff works so I can figure out a better approach to troubleshooting it. Thanks again and have a great weekend!!

[Jazz P Bass]

[QUOTE=tonecat;232678]Twhat do you mean by "static check the output section"? QUOTE]
Static check is with the power off.
Resistance readings. Diode check of transistors.

Dynamic is with it on.
Voltage & current readings.

If you can follow the circuit & things check out resistance wise, then you can feel pretty confident when you turn on the amp.

[Enzo]

What components are moved? And more importantly, are they parts involved in the repair?

I only have one version of PV2.6C in my files too.

[tonecat]

Hello again folks,
Sorry I didn't post anything sooner. My internet was down over the weekend. Anyway, I included a couple of photos of the board layout. As you can see there are quite a few differences between the schematic board layout and my actual layout. Also note how hot the board got around the power resistors. I am waiting on parts to come in. I am replacing all the power transistors (part #'s MJ-15015 and MJ-15016), the driver transistors (part #'s 5331 and 5332), and the triacs (part #'s SAC-187) which I ordered from Peavey. I marked the location of the original parts on my board before removing them when I saw there were differences in the layouts. I am really concerned about just putting these parts back in without doing any other tests. Jazz P Bass suggested checking the bias transistors and associated components. I am not sure which parts he is talking about? Maybe Q101 and Q201 and the string of diodes? With the board layout being different, it will be much harder for you gurus to point me in the right direction for further diagnostics. I wish this was more like a tube amp where you can fire it up without the tubes in it to check other voltages that I could compare between the two channels. The schematic is a little light on voltage readings anyway. I might be overly concerned about nothing and just replacing the parts may be all this amp needs. Then again, I don't want to trash over $30.00 in parts either. Any ideas or help would be greatly appreciated!! And as always, Thanks!!

[Enzo]

The three resistors between the main filter caps? See the two silver diodes, one above and one to the left? Those are 15v zener diodes, and when one shorts out, it will burn up its resistor. That is what those resistors do.

I can't read it from the photo, but there is print in the foil pattern lower left corner. I can see PV2.6C but is there any indication of a revision level? Or mention of a year? Gather up all the numbers and stuff from that legend down there, and contact Gene Ford at the factory. Ask him if there are other revisions that are documented.

And just in the name of science, ask him if they can service the board if sent by itself.

Oh never mind, here, you have the first cut of the board.

[52 Bill]

...I might be overly concerned about nothing and just replacing the parts may be all this amp needs. Then again, I don't want to trash over $30.00 in parts either. Any ideas or help would be greatly appreciated!! And as always, Thanks!!

Use a light bulb limiter when you power up after the repairs and you will not have to worry about ruining the new parts.

[tonecat]

Thanks for posting the correct schematic and layout Enzo!! Much easier to track down where the parts are. I checked the zeners (CR118 and CR121) and the 700 ohm resistors (R141 and R142) and they were all good. Must be these just get warm during normal operation? I static checked all the other parts in the output section on the board and found one open diode CR210. I believe that is part of the bias string? Other than that, all other parts passed the tests and were similar from channel to channel. As soon as I get the parts, I will replace them and fire it up using a limiter. I will report back with the results. If there is anything else I should check, please let me know Thanks Again!!

[tonecat]

Well I got all the parts in today and put the amp back together. I fired it up using a light bulb limiter and all was good. According to my Sencore Powerite, it was drawing right at 50 watts from the mains at 117vAC at idle. I was really glad that I spotted that open diode (CR210) so I didn't have to do any more troubleshooting after I put it all back together. The amp works and sounds fine and all voltages are consistent between the channels and are in spec. The only thing that bothers me is how hot the power resistors (R141 and R142) get in this amp. Way to hot to touch. I guess I never noticed they got that hot. But I guess that is a byproduct of what they do. All in all, another successful repair!! Thanks again for all your suggestions and pointing me in the right direction. With the exception of the diode, my initial thoughts were that the outputs, drivers and triacs were bad and they were. I guess I am finally starting to figure out a little bit more about this solid state stuff. Does anybody know of some good sources to find more semi easy to understand info on solid state amp repair? Thanks again to everyone here. This is the most helpful forum with the most knowledgeable people. I don't need help with every amp I fix, but it is nice to know I can come here and get some answers if I need them. You guys Rock!!