90's JCM 900 hum on High mode

[pontiacpete]

The low mode doesn't seem to hum at all. There had been some arcing near the switch and the traces under the B+ wire adjacent to the switch got chard. I thought the pcb in the area had become conductive, so I clipped that trace and ran a wire with the insulation , but it still hums . Ive checked all the resistors in the area R30, R35, R31-33 and 54 . None are open. I tried jumping out the 50/50 500vdc filter caps and it still hums. I tried new power tubes .,, tried new preamp tubes, tried running the amp with out the preamp tubes in and still no luck.
Has anyone every come across this type of problem?

THanks,pete

[gomez63]

without a photo, it makes it tough to know (better)...however, did you check voltages on the output tube sockets, check those component values around the burned areas, check/replace the switch if it was involved with the burn and look for bad solder points in the high power tracing?

The voltage/value assessment should give you a clue.

The key thing to keep in mind is that there was obvious component failure somewhere to cause a burn....track down that failure.