Fender BXR300C w/broken trace...?

[acorkos]

when i tap on the pcb with just the right force, the amp starts humming (buzzing) loudly, front panel controls have no effect. the yellow compression LED lights up when it's humming. no broken component leads, and i have resoldered all the connections, but still no change. the humming starts with lighter tapping when i tap on the left side of the board, where the large filter capacitors, large diodes and large cement resistors are located. also, when it's humming, the +70V drops to about +45V....no change to the -70V rail. i'm thinking there must be a crack on the pcb somewhere at one of the solder pads, but i can't get it to show itself when i push and tug on the various component leads. any ideas? thanks for your help!

[Enzo]

Your +70 drops to +45? OK, when you measure that +45, flip your meter to AC volts. I bet you get a fairly high reading.

Your +70 filter cap is either failing or has cracked solder or broken traces. Remove the cap completely and see if any of the pc trace material comes off with it. You might have perfectly solid solder connecting the cap to a trace pan thaqt is cracked away from the circuit.