Fender Deluxe 112 Plus - 100Hz nasty buzz

[Reiser]

Hello,

I'm working on a Fender Deluxe 112 Plus
One of the output transistors had been screwed directly on the heatsink without a silicone pad, which led to a zap, a broken pcb trace and shorted output transistors.

Trace is restored, new output transistors, preamp stage is fine, power supply is fine, but there's a 0.2VAC 100Hz buzz at the power amp output and I have no idea why.

Buzz is not responding to the volume control. Can you help me troubleshoot this amp ?

Here is the shape of the buzz :



Power supply ripple and power amp output :



Schematic added

[Enzo]

100Hz is power supply ripple. You had it all apart and back together, so first thing I check is the two large main filter caps. If it didn't hum before and now does, I'd suspect you cracked the solder under one of them. As it runs, try just pushing against those caps, does it make the hum intermit? I'd resolder them to be sure anyway. I find failed solder on those larger parts on a lot of SS Fenders.

[Reiser]

Hello Enzo, thanks for the answer
Main filter caps had been tested ok and resoldered, and main ripple is as shown on the second picture, 400mVpp ripple ; is the filtering good enough ?

I tried and hit the chassis several times until i got slight differences from the buzz :

https://imgshare.io/image/rNVTUH
https://imgshare.io/image/rNVcFd

I will resolder every component on the power amp board and report back