One important thing @bholder suggested was to take your batteries out before you open up the control panel - it is pretty tight in there and if you touch the wrong thing to some other thing and the batteries are still connected, it could fry something. So for the safety of the bass electronics, take your batteries out if you open her up.
The preamps died when they were in the control panel, sealed. I never removed the control panel until the active circuit went dead.
). Keep us posted!