Peavey Musician 400G

[nickbme07]

Dude, to answer your question on the + side of C36, I started from the diodes to see where the 15v started to drop off and its after C36 I see the voltage, but not after C40. This path is what led me to find the R70 testing of the 15k to be off.

Also, I now see it is possible (from physical burn indication on trace and mount point) that I missed a cap discharge before taking power board out at some point and the -52v rail (bottom trace) shorted to ground via the mounting lug. This most likely happened after it was half working.. Maybe some ideas where to look of what may have been damaged in that path?

[Helmholtz]

Also, Is it normal that L1 is a 4.7k resistor and not the 100mh inductor?

No.
L1 is in parallel with a 4.7R resistor (R44). 4.7k in parallel with 4.7R makes no sense.
I guess L1 is needed for stability reasons, i.e. to avoid HF/RF oscillation.

[The Dude]

...... Maybe some ideas where to look of what may have been damaged in that path?

I gave suggestions and asked questions in post #24 that are still unanswered. One step at a time.

[nickbme07]

The + side of C40 is your 15v rail. What is the resistance from that rail to ground? That rail supplies pin 8 of the op amps. If it measures low resistance or shorted, you'll have to start disconnecting things from that rail until the short clears. It could be an op amp. It could be a cap. It could be the regulator itself, etc. What is the voltage feeding the regulator or the + side of C36? Check op amps with your finger. Are any of them getting hot? If so, that's a clue. Unfortunately, there's no fast way to find a shorted rail. It could be anything connected to 15V.

Sorry Dude, I had only answered some of these questions - distracted by total failure + late nights. Anyway, back to your steps - C40 + rail to ground resistance comes up 3.9k, negative side is 0.1ohm. Voltage seems to be ok (moves up with variac) at the+ of C36, but no +volts on C37. + side of C36 shows around 400k ohm and drops, + side of C37 shows 0.1ohm. All references with ground on chassis

[nickbme07]

No.
L1 is in parallel with a 4.7R resistor (R44). 4.7k in parallel with 4.7R makes no sense.
I guess L1 is needed for stability reasons, i.e. to avoid HF/RF oscillation.

This is what I was thinking as well. I found literally (2) of the same resistors side by side at R44 and L1 positions. I pulled a leg on each and both test to 4.7k (my apologies I typo'd the 'R'). L2 is an inductor as well, but has a large one in its position.

[Helmholtz]

This is what I was thinking as well. I found literally (2) of the same resistors side by side at R44 and L1 positions. I pulled a leg on each and both test to 4.7k (my apologies I typo'd the 'R'). L2 is an inductor as well, but has a large one in its position.

So both 4.7R or 4.7k?

[nickbme07]

So both 4.7R or 4.7k?

Both are 4.7k, physically same resistors.

[Helmholtz]

Both are 4.7k, physically same resistors.

I don't think that could work. Needs low resistance here. Voltage drop should be 0.02V.

Any signs of former repair?

[nickbme07]

I don't think that could work. Needs low resistance here. Voltage drop should be 0.02V.

Any signs of former repair?

It doesn't seem that way, but there is no telling for certain. The original 2 main filter caps were of different brands (one basically expanded and abour was burned up). When i foind a resistor at L1 I defitely was baffled. The solder look stock to me in that area too.

[nickbme07]

(I renstalled it backwards) L1 is on left.

[Helmholtz]

(I renstalled it backwards) L1 is on left.

So what do you actually have there now?

[nickbme07]

So what do you actually have there now?

Still the 2 resistors it came to me with. I uploaded picture in my previous reply.

[The Dude]

Sorry Dude, I had only answered some of these questions - distracted by total failure + late nights. Anyway, back to your steps - C40 + rail to ground resistance comes up 3.9k, negative side is 0.1ohm. Voltage seems to be ok (moves up with variac) at the+ of C36, but no +volts on C37. + side of C36 shows around 400k ohm and drops, + side of C37 shows 0.1ohm. All references with ground on chassis

Those readings don't show any dead shorts on the rails. Note that the + side of caps on the negative rail are ground, so you shouldn't have voltage there. Are you still missing your +15V rail? What are the voltages in and out of the 15V regulator?

[nickbme07]

Those readings don't show any dead shorts on the rails. Note that the + side of caps on the negative rail are ground, so you shouldn't have voltage there. Are you still missing your +15V rail? What are the voltages in and out of the 15V regulator?

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.

[nickbme07]

[QUOTE=Helmholtz;n968690]

Watching the volts here ramping up the variac, i found 6VAC with 20VAC mains applied (both sides of resistor)