Peavey Musician 400G

[g1]

The diodes should be reverse biased when installed. So cathode of one goes to +15 rail (anode to ground). Other one goes anode to -15V rail and cathode to ground.

[nickbme07]

The diodes should be reverse biased when installed. So cathode of one goes to +15 rail (anode to ground). Other one goes anode to -15V rail and cathode to ground.

Thanks, Sounds like they are backwards. I will check later when I get back to it tonight.

[nickbme07]

Thanks, Sounds like they are backwards. I will check later when I get back to it tonight.

They were in fact backwards on each. Can't say honestly if it came that way or not, unfort I did not get a picture of the solder side. I flipped them and still don't see a positive output on VR1. Most likely toasted. Monday I will get the regulators. Is there any way I can test that these diodes are oriented properly before toasting another regulator? Thanks!!

And why the hell aren't they on the schematics? I didn't see on any of the models.

[g1]

Is there any way I can test that these diodes are oriented properly before toasting another regulator? Thanks!!

And why the hell aren't they on the schematics? I didn't see on any of the models.

See blue edits to your pics for correct orientation.
They are not shown on schematic as someone added them as a reliability mod. Somebody probably read about it on line and installed them. But the issue they were dealing with was only happening with certain brands of older regulators.
With modern regulators you don't need them. So if you are replacing both the regulators, you can just remove them.

[nickbme07]

Fantastic, that's what I was thinking as well. Thanks for the verification!

[nickbme07]

Replaced both regulators. Removed the 2 diodes on solder side. The 79 shows negative output and C41 shows its -dc ok ramping up variac. Same as before. The 78 is acting the same as well.. -1.2vdc on output and C40.

Any next recommendations to check without taking everything off the rail?
Can I lift the leg of the VR1 (78) to check its putting out voltage without messing up the rest of the circuit with the negative side still running? I don't think it's necessary however.. I do see the C40 go positive volts initially and its shortly after (around 10vac mains) I see it drop below into negatives. Seems something is shorted on the rail still.

[g1]

Are the input voltages to the regs. staying stable + and - ? (C36 + end, C37 - end)

[The Dude]

Have you changed the regulatore, yet?

[nickbme07]

Yes, as mentioned I replaced both regulators.
But then it was after some hunting on the rail I found (C24 (NP)) to be basically open when out of circuit. Not sure if it's been bad or happened when regulator went out (keep in mind the regs are only rated for 0.5amp so a short can easily fry it).

Replaced the C24 and the +15 rail (C40) came to life.
SHE LIVES!!!

Outside of some scratchy pots (despite already deoxing them) and maybe some caps needing replacing on the preamp board now, everything works 100% including autotransformer and reverb tank.

Thanks everyone for your help and support!!

[The Dude]

Open C24 wouldn't cause a 15V rail problem. I suspect something else happened during your repair. Also, what are you checking caps with (C24) and what do you mean by "open"?

[nickbme07]

Open C24 wouldn't cause a 15V rail problem. I suspect something else happened during your repair. Also, what are you checking caps with (C24) and what do you mean by "open"?

Sorry i need to work on my wording. I meant that it had no resistance, or shorted.

[nickbme07]

What could be causing a big pop when turning main power off after using amp? Possible the diodes were added to suppress this? All the capacitors in the power section are pretty much new. Nothing changed on preamp board at this point, so possible something from the lytics there but wanted to mention before shotgunning preamp (?) Thanks guys!

[glebert]

Power up/down thump is pretty common, especially on solid state amps, but I don't know if that is what you mean.

[The Dude]

Part of it might be the lack of that cap you clipped out across the power switch. That cap was to prevent arcing at power up/down.

[nickbme07]

Part of it might be the lack of that cap you clipped out across the power switch. That cap was to prevent arcing.

I was going to ask about that, but it seems to be a death cap in essence, no? If it fails short. Shouldn't it be at least replaced with a modern safety cap of same type?