Peavey XR560 PA head

[lowell]

This came in with a broken fader. Sound would cut in and out when the fader was moved. Also there was no sound from the speaker output on the back but there was sound on the front from the monitor and main outs. I replaced the fader and now there's no sound. Also all of the LEDs along the top of the faders except for the 1st two are on. These are the feedback LEDs that help with feedback when using the PA. So maybe there's an oscillation happening. In any case I DO GET SOUND from all output jacks when I use my signal generator, but only when I get the input signal up to 1v p-p. Up until 1v p-p there is no sound and then bam, sound.

[lowell]

Anyone? Why would a larger signal work but not a lesser one?

[Jazz P Bass]

Lowell, the post is confusing.
What where the problems when the mixer was received?
No speaker output?
Bad Fader?
Monitor Out was good.
It sounds like there are issues after the fader repair.
Clip LED's are lit.
No output from Monitor Out.
Input requires a 1 V signal to trigger.
I would check every one of the connections on the interboard wire harnesses.
They love to break when they get flexed a little too much.

[lowell]

There was intermittent sound when the broken fader was pushed around, but only out of the monitor and mains outputs on the front. Nonetheless I found the issue. Aside from the broken fader there was a very elusive break between a trace and solder pad. It was invisible to the naked eye. I was finding no +v on pin 8 of the preamp opamps so it was obvious that that was the issue. I DID find the +15v in the power supply AND on the board close to the power supply, but not further down the board to the actual channels. I began tracing for continuity and eventually found the broken trace. I hope I remember that lack of one side of a dual opamp supply can allow an amp to work with larger input signals.