ADVANCED Troubleshooting

[Dust-man]

I'm not sure if I posted this in the right spot, but who cares. I have a Crate G600 amplifier head, when I play it the volume level will constantly go up down and get really distorted. I took a looksee inside and there are no burnt out resistors, loose wires, lose jacks, cold solders, or anything of that nature. I also plugged my guitar into the fx return to see if it was something in just the pre-amp channel, but it made the same doggone noise. Now I'm really confused, because it does this more often then when I first got it, by the way, its used, not new.
If anybody can help me, You'd be a big blessing. Thanks.

[syndromet]

I'd spend a few dollars, and try to change the chip or transistors. If that doesn't help, I'd rip out the guts, and build a Lm3886 with a krank pre.....