A common problem in noisy playing environments: instrument starts to hum and buzz. This is I guess made in Japan Precision bass and it didn’t have any kind of metal plate behind the pots or shielding in the cavity. These basses are easy to work with because they are so simple and repairs like these don’t take a lot of time.
Hum wasn’t that bad to start with but I decided to shield at least the cavity and replace old pots and jack. First I took all pots and jack out and shielded the cavity and backside of the pickguard with conductive adhesive aluminium tape. Next I installed new CTS 250k potentiometers. When upgrading japanese/metric pots with solid shaft CTS ones remember that CTS uses 6.35mm shafts compared to 6mm ones used by their metric/split shaft sisters.. :) You can test matching potentiometer knobs by using a 1/4″ guitar jack: if the tip fits inside the knob the pot shaft will fit too. Also the mounting hole for CTS needs to be 9.5mm instead of commonly used (Alpha) 7,8mm. So drill them bigger. For output jack I used a Switchcraft #11 which is the only mono jack I use these days, they are really really good.
When doing shielding stuff like this or when fixing grounding problems always check continuity between the bridge and ground plane inside control cavity (or guitar cord sleeve). If there isn’t a connection something is wrong and your grounding isn’t working.
After this I did a full setup and installed new strings. No more hum :)