As it is stereo, you have a good channel to compare with. Use a multimeter
to compare resistances (no power applied) or voltages (power on) at the
components working back from the outputs of each channel. When you find a
difference you have located a faulty component/region.
If you can get an oscilloscope it can also be used to trace the path back
from the output of each amp.

As you say an output is blown (which covers many possibilities) look for a
fuse or output transistor (3 legged thing screwed to a metal heatsink/case)
first.
Your ability to fix this depends on your knowledge of components, past
experience and logical thinking capacity. You haven't given us much to go
by.

Good luck
Russell

"t-bone" wrote in message
oups.com...
anyone know how to diagnose a blown left channel on this amp? there are
no signs of anything burning or frying.