Sometimes, it's not that hard to open it up and see what's wrong.
Unplugged, of course.
Look for burn marks, leaking or bulging capacitors, etc.
Capacitors and resistors are pretty easy to replace, though you do need to take care to drain capacitors before messing with them. They hold a bit of a charge for a while.
You can find out about this stuff online.
I mean, I'm not an expert, so proceed at your own risk, but I've so far saved a pair of studio monitors and a Peavey Classic 20 by swapping out a single, super cheap capacitor.