HBE Powerscreamer problem

[BarnabyHooge]

A friend of mine has been playing a used HBE Powerscreamer for a couple years now. Recently, the Level pot stopped do anything when turned. It still plays, everything else is working, it's just the level knob seems to be stuck. I figured the pot was busted, but I tested is and it seem to work just fine. I don't know enough to really get to the bottom of this , so I'm turning to you all. Would a bad chip cause this? The things socketed, but the top has been gooped to hide the type of IC. I know there is a serious lack of good info, but I just thought I'd through it out to see if anyone could help.