I have a mid-90s GK 400RB, and am experiencing an unusual problem. The amp will unexpectedly shut off output volume - the power and boost channel light are still ON but zero volume. No noise or crackly scatchy sounds - the volume just dies. Powering off and back on it will then work normally. The amp is not thermally hot, fuse is fine, and it's connected to a 4-ohm GK cab with a new speaker cable. I have ruled out my active basses and instrument cables. Could this be a bad pot? Has anyone else had a problem like this? THANKS!