chris:
The "hint" in the reply post by Allodoxaphobia is right on. You have
a good channel to make comparative component and circuitry tests with
the bad channel ..... both channels have identical parts so it doesn't
get too much easier that this. In a pinch, you can "borrow" parts from
the good channel to verify possible repair and parts replacement
solutions so you can, with confidence, order any semiconductors or
other components not locally available. Get your DMM out and start
testing and comparing. Additionally an audio tone generator and scope
may be of further assistance in finding where the signal is and where
it isn't.
electricitym
..
..