Try this: Plug the bass in. With the back cover unscrewed, try touching with a small screwdriver's tip each soldering point related to the hot audio wire path (ie, the jack, the volume pot, the balance pot) and check where it does sounds, where it does not, and how (low or high volume, meaning after or before the preamp),. that will give you an idea of where the failure would be...
(Message edited by jcdlc72 on November 26, 2009)