Bass with a mystery noise:

I was brought an 80's Fender Squire bullet bass because after plugging it in an amp and playing it for a few minutes, it would get noisy, start to crackle, and then cut out altogether.  I suspected the amplifier, because it sounds like an issue related to the amp warming up, and a bad contact coming loose due to expansion caused by heat.  The circuit in a guitar doesn't produce enough heat to have this kind of problem.  The owner assured me that it did the same thing on both of his amplifiers, so it only made sense to take him by his word and call it a mystery for the time being.

I plugged the bass into my amplifier, and besides having a bad volume pot that did work all the way up, wouldn't you know it, the problem did not show up, even keeping it up and running for a few hours and playing it every once in a while!  My thoughts went back to amplifier trouble, but I just couldn't see him lying, and willing to pay me to chase a ghost, so I cracked it open to give it a closer look and see.  It's not like I haven't seen stranger things.

The ground wire to the strings was spliced instead of replaced.  That's not what I call neat wiring, but unlikely the source of the problem.  The signal wire from the jack to the volume potentiometer had most of its wire strands removed with the insulation, due to using a knife, or the wrong notch of a stripping tool. It was hanging on the pot's contact by a mere thread, and fell off merely from me maneuvering the pick guard around while working on it.  Although bad, this was still not enough to cause the odd behavior.  Here is a picture, after I disconnected the ground wire from the jack too.

The bass was rewired by someone before my client purchased it, and the job was done very sloppy, with gobs of solder on the contacts, including one real big one inside one half of the split single coil pickup that was touching the windings.  It looked like the the person who did the wiring had the misconception of the more solder, the better, and jest kept adding it not realizing it was running through the eyelet and collecting underneath.  Check this out:

Now this is the likely culprit.  It had nothing to do with heat after all, but rather movement.  The blob of solder was on the grommet connected to the inside of the coil, but burned off some lacquer insulation on the coil it touched during soldering.  When it cooled down and contracted it didn't touch the coil anymore, and everything seemed OK, but since the pickup is not wound very tightly, enough movement allowed the coil to touch the blob and short it out.  When I played it I didn't jump around and rock out, but handled it more gently.  I hooked it straight to the jack, and tested it again, and sure enough after banging around on it, it went dead.

I removed the solder blob, and rewired the pickup using a shielded cable to reduce noise.

The volume pot showed signs of being overheated, and the resistive coating inside was most likely burnt to a crisp.  The potentiometer was really noisy when turning it, and lost most of the volume turning it from 10 to 9, and went completely quiet at about 8.

I replaced the volume potentiometer and rewired the rest of the instrument, using high grade shielded cable to reduce noise.