SWR model LA 12 60 watt bass amp powers up but only hums (suspiciously like 60Hz?). A friend gave it to me to, thinking I might be able to fix it.
One chassis attachment screw is missing, and others show marking that it has been opened up previously.
At first it almost started to amplify a test signal, then it started thumping the speaker several times per second. When I powered it off it let out a squeal that rose in pitch until it quickly faded. Insides have a faint burnt electronics odor.
I may have identified what looks like a dry solder joint at the (marked "+") leg of what is labeled BR1 (bridge rectifier?).
Photos to follow.