[julie_m]

I'd tend to agree with the diagnosis that the output transistors on one or both channels have failed short-circuit. You will have to unsolder them from the board to test properly, but a C-E short is usually blindingly obvious even in-circuit.

About four times out of five in my experience, if the output transistors of an amplifier have failed short-circuit collector to emitter, they're usually the only faulty parts. If they are trying to pass too much current (perhaps because there are too many speakers connected and being driven too hard; or if a short-circuit gets applied across the output) they tend to fail in this manner, and their demise -- or rather, the consequential sudden loss of power when the fuse does exactly what it is supposed to -- tends to protect the rest of the amplifier circuit. So it's often worth taking a punt. Get the part numbers (make appropriate substitutions if exact replacements are NLA) and if they're cheap enough, just replace them. If you are lucky, the amplifier will Just Work and continue to give Years of Trouble-Free Service.

The fifth time is ..... well, let's call it a good one for a masochist. In this case, something else is faulty and that is what is killing the output transistors. Let's just hope it doesn't come to that. Still, with a stereo amplifier, at least you usually have one working channel to compare against.