My Ampeg (i.e. Crate) SVT-350H bass amp has been on the fritz for several years. I took it to Musical Instrument Repair on Highland in Memphis twice (that I can remember) each time to be told "There's nothing wrong with it." I hate that place. Never go there. I think it was those experiences that really made me want to learn about the inards of my amps et. al.
Several years ago I had a friend rig the fan so that it runs all the time at high speed instead of the stock "run when a little temperature diode that sucks overheats." The fan wouldn't run and the amp would overheat and shut down. So that's fixed. Fan always runs. It's a loud fan and kind of annoying but at least nothing cookc inside.
I've read online that the fan not running is a problem with this amp build (which is also used for the B2 I think). It's possible that the overheating burned something out, but at times the amp works perfectly. I'm hedging my bets against something being burnt.
There is a relay (the K1 relay) that stops the amp from popping the speakers on power up. I think this relay is causing the problems. I bought a replacement from Mouser for about $17 w/ S&H. I'll wire it in when it shows up tomorrow and see how things go.
I'm a little disappointed in myself with this project. I could really dive in with my multimeter and try to actually hunt down the problem for sure instead of just replaceing the thing I think is broken and hoping for a good outcome. I'm still worried I don't know enough to not electrocute myself I guess. I'd rather run the safe route, but I learn a whole lot less in the process. Eh.