By "intermittent R side" are you saying that the audio is sometimes present and sometimes not? I assume the second photo is showing the L channel passing signal but nothing on the R channel. Does flexing the boards, cables and connectors bring the R channel back to life, or does it suddenly return on its own? Do you have schematics? Can you tell from scope probing whether there's a point in the R channel signal flow where, for example, the signal is stuck at a power rail value (saturated)?

A bit off topic but it looks pretty cool. Looks like something I would use for keyboards. Fun seeing inside it.

Boswell wrote: By "intermittent R side" are you saying that the audio is sometimes present and sometimes not? I assume the second photo is showing the L channel passing signal but nothing on the R channel. Does flexing the boards, cables and connectors bring the R channel back to life, or does it suddenly return on its own? Do you have schematics? Can you tell from scope probing whether there's a point in

From What i can tell the problem is at the final output amplifier for the right side of the 2nd bus output.

Spot on Boswell, yes the channel returns if i wiggle or touch the main channel 2 output pcb the signal returns.  I thought at first it was cable problem, but I can not pin point which cable is causing the drop out. Also when I increase the input signal to the board the R channel returns to the output.  Could it be a return path issue....?  Flexing the board seems to have the same response as touching the pcb, the signal returns. 

 

I do not the schematics, nor can I find them.

 

From how you describe the problem, I would be inclined to think it's a dry joint or a faulty component rather than a cable. If you can get it to stay in the failed state, it should not be too difficult to chase the signal through the circuit using a scope. Send the same input signal to the two output channels, then you would have something to compare against as you walk through.

The main bus two output Op-amp was the culprit. When I resoldered the pins tied to common, the problem disappeared....

Well found! I thought a dry joint would be the most likely option.