[Mike Rivers]

On Mar 22, 8:52 am, Brian wrote:

I don't know if this could be as simple as a connection came
unsoldered inside, or if an internal component might actually need
replacing. What are some possibilities, and what non-obvious things
should I look for when I open it up? Things I can test with the
multimeter?

All of those are possibilities, but a multimeter won't tell you very
much. The best troubleshooting tool (along with a schematic and the
knowledge to read it, of course) is an oscilloscope so you can put in
a steady sine wave signal and see how it changes as you move through
the channel signal path. Next best is a headphone amplifier and a
probe on the input so you can at least listen to tell if the signal
drops significantly when it shouldn't or if it becomes distorted at
some point.

And while you're probing around in there, maybe you'll stumble on a
loose connector or bad solder joint.