My Yamaha RBX-170 needs a new tone control. I don't know what happened but it looks like the tone knob may have taken a hit because the knob spins "wobbly" and the control seems to have no effect on the sound. I opened it up and looked. It is a pretty small pot in there. I have no idea what I should get to replace it. I'm looking for information on the subject and links to online stores that would have a suitable replacement. I've never had to replace any electronics in my basses before. Thanks!