Peavey Musician 400G

[The Dude]

CR21 and CR22 show voltage increasing as i go up on variac. I can supply 15v to C35 if i was able to get to 120v on mains. I stop at around 50v when i get the audiable (10v dc on 15v rail (at C36+))

Im also doing tests with the autotransformer molex disconnected. Output jacks molex is connected.

...... and what do you have at the regulator output (C40)?

[nickbme07]

...... and what do you have at the regulator output (C40)?

30v mains, on C40+ im seeing -0.7vdc. C41+ shows -6vdc

[The Dude]

For clarity: Is that negative .7V or is the "-" just a dash? If that voltage is negative, it likely indicates a shorted op amp and negative rail is leaking to positive rail. Try unplugging the molex connector that applies power to the preamp board. Then see if your 15V rail is still low or comes up closer to the negative rail. This will at least tell us if the problem is on the preamp board or the power amp board.

[nickbme07]

For clarity: Is that negative .7V or is the "-" just a dash? If that voltage is negative, it likely indicates a shorted op amp and negative rail is leaking to positive rail. Try unplugging the molex connector that applies power to the preamp board. Then see if your 15V rail is still low or comes up closer to the negative rail. This will at least tell us if the problem is on the preamp board or the power amp board.

Yes it's negative. Ive had the preamp board disconnected since it stopped working.

There's the opamp on the power board. Stock is a 4558CP, I have some TI RC4558P and JRC 4558D on hand. I tried the 4558P and it yielded same results.

[Helmholtz]

(I renstalled it backwards) L1 is on left.

Don't see any 4.7k resistors in the pic. The yellowish part on the left should be C26.
I case of doubt measure DCR of the part. A cap will read open (O.L.), an inductor should have a low DCR.

[nickbme07]

Don't see any 4.7k resistors in the pic. The yellowish part on the left should be C26.
I case of doubt measure DCR of the part. A cap will read open (O.L.), an inductor should have a low DCR.

3 and 4 over from C26 is the L1 and R44 in the picture we were talking about.

[The Dude]

Layout in the schematic shows this (not what your pic shows). Did you maybe remove the parts and reinstall them wrong?

[The Dude]

You need to stop randomly removing/changing parts and concentrate on solving the problem with reasonable troubleshooting. You are just creating more problems. It started with unnecessarily rewiring the power switch and removing a cap, then replacing perfectly good .01 caps, now messing with other circuits that have nothing to do with the problem. I don't mean to sound harsh, but I think you're creating more problems than you are fixing.

[nickbme07]

Layout in the schematic shows this (not what your pic shows). Did you maybe remove the parts and reinstall them wrong?

I dont understand why you say my picture is wrong - everything i right besides the L1 position having the resistor in its place. No I only had removed L1 and lifted the leg of R22. The only thing I did with L1 was reinstall it backwards. Originally the stripes were lined the same with R44.

[Helmholtz]

3 and 4 over from C26 is the L1 and R44 in the picture we were talking about.

From left to right (I think): 180p, 47R, 4.7R, 4.7R.

No 4.7k, no L1.

[The Dude]

If that's the case, then my apologies. The schematic clearly shows L1 in parallel with R44, which is not what your picture shows. Maybe there was a factory revision to the circuit or someone else was messing with the amp.

[nickbme07]

You need to stop randomly removing/changing parts and concentrate on solving the problem with reasonable troubleshooting. You are just creating more problems. It started with unnecessarily rewiring the power switch and removing a cap, then replacing perfectly good .01 caps, now messing with other circuits that have nothing to do with the problem. I don't mean to sound harsh, but I think you're creating more problems than you are fixing.

But thats not accurate, Dude. First off i changed the input switch, yes. We can look at if the additional cap is needed, which is why i mentioned it.. we semed to blow passed that (rememeber power amp was working with 120v mains off limiter). The .01 caps were not all bad, no, but im nlt going to replace just 2 out of the 6. They were the oldest nastiest looking components on the board. Also lifting legs to check them made them only deteriorate more. Anyway, there are perfectly good caps in there now, and i questioned if the Mylar film was OK, did i not? Since the only thing ive done is taken vomtage readings and nkw changed the opamp to test (easy enoug) since yoh mentioned a possible short (maybe in the preamp, but none the less i hadnt tested a single ompamp in the amp yet).

So i appreciate any help you can offer, based on the test results ive posted - i dont know what else youd like me (not) to do while we are trying to find a short?

I also remember that the amp started failing before I changed out the .01's, they were just on my next to do list, but im with you - I was trying to change as little as possible to first get the amp up.

[nickbme07]

From left to right (I think): 180p, 47R, 4.7R, 4.7R.

No 4.7k, no L1.

Ok help me get on the same page here..
Is that not L1 listed right there?

[The Dude]

From left to right (I think): 180p, 47R, 4.7R, 4.7R.

No 4.7k, no L1.

I think what you are calling a 47R (blue) is probably a coil. The problem here is that I don't think the schematic exactly matches the circuit, which makes things difficult.

[The Dude]

But thats not accurate, Dude. First off i changed the input switch, yes. We can look at if the additional cap is needed, which is why i mentioned it.. we semed to blow passed that (rememeber power amp was working with 120v mains off limiter). The .01 caps were not all bad, no, but im nlt going to replace just 2 out of the 6. They were the oldest nastiest looking components on the board. Also lifting legs to check them made them only deteriorate more. Anyway, there are perfectly good caps in there now, and i questioned if the Mylar film was OK, did i not? Since the only thing ive done is taken vomtage readings and nkw changed the opamp to test (easy enoug) since yoh mentioned a possible short (maybe in the preamp, but none the less i hadnt tested a single ompamp in the amp yet).

So i appreciate any help you can offer, based on the test results ive posted - i dont know what else youd like me (not) to do while we are trying to find a short?

Again, my apologies. I have resigned myself to the fact that the schematic just doesn't exactly match the circuit. Onward, then. Did you try replacing any op amps, yet? I'd concentrate on that lack of +15V, since that definitely appears to be a problem. You don't really have to replace op amps for testing. You can unsolder pin 8 of them if you have a good desoldering tool or just remove them and recheck the +15V supply. If you find one that allows the supply to come up, then replace it. It could also be a regulator problem, but that negative voltage on a positive supply makes me think it has to be a device that shares both neg and pos supplies (op amps).