Preamp Problem: Help Please

[vpermana]

Hi Luthiers,

Yesterday my onboard preamp on my jazz bass was acting out. FYI, to activate the pre-amp it uses a push pull knob which also happen to be the bridge pick up volume.

I made some observation on my bass when preamp was functioning today for a few times:
During passive and active mode: when I backed down the bridge pick up volume a little a bit, there is an expected "normal" hum noise volume. The volume of the noise is at the same level as when I backed down the neck pick up volume.

However, when the preamp is not functioning even when I activated it:
During passive (with and without battery) and active mode (with battery): when I backed down the bridge pick up volume a little a bit, there is an unexpected "louder" hum noise. On the other hand when I backed down the neck pick up volume. the hum noise for this particular pick up is a lot less than normal/quieter.

During Active mode, Bass and Treble were both working fine, meaning I was able to hear different tone under both condition (preamp functioning and not functioning) but lack of volume when the preamp is not functioning during active mode.
In other words, the volume during active and passive mode, both stays the same level. Under normal condition, active mode usually sounds a bit louder than passive mode.

Questions:
1. Does this mean the push pull potentiometer at the bridge pick up volume has gone bad?
2. Is this a common problem where local tech would be familiar with?

Please advise.

Thanks