The B30
here does not have a barn door which is what I would expect.
Guessing, I would expect whatever circuitry is present is inside the bass side shoulder under the controls. The transducer is under the bridge and there are a few wires connecting everything. Battery velcro'd somewhere.
Any luthier or tech who is competent enough to replace the existing system should be able figure out how to rip it out as well.
Repair does not have to be rocket science at least until all the wires and connections have been checked.
I also have to ask, why? Is this one of those 'it's broken so it must be fixed' things or will it actually be used with the electronics? If I need the amplification my first approach is to use an electric bass and not use the B50 with its pickup.