[Skler]

In general, though, these amplifiers are not worth the money to have a
tech look at them, and probably aren't worth your time to open them up
unless you value your labour very little.

If you open it you'll probably find two big rails and two small rails...
and if you measure them you'll probably find one or more of them is dead.



Yep. In the US, it's generally $100 or so just to have a good take an
amplifier in for evaluation, so as a general rule unless the amplifier is a
very good one, it won't be worth having repaired. On the positive side, if
the problem is with the power supply as suggested, that will usually be a
lot less expensive to repair than say, output and/or driver stages. If the
supply is of the switching variety, which is becoming more common in audio
power amps these days, the power supply module is almost never repaired, but
simply replaced. Such a repair can easily cost in the neighborhood of $100
for the supply alone, plus the cost of labor. For relatively inexpensive
amplifiers your best bet will be to either work on it yourself or have a
technically inclined and interested friend open it and look for simple
problems like broken connections, loose crimp connections, cracked solder
pads, blown fuses or obviously burnt up components and go from there.

Good luck!

Skler