Reparing electronics for a jazz guitar or other semi-hollow guitar without a good entrance is of course more difficult and takes more time. Usual the complete wiring have to be taken out, including the output, to reach the actual defect. Some guitars can be approached by the pickup space, other guitars only have acces by the two F holes.
It is very important to solder the wiring accurate and shock proof. All contacts have to be isolated from grounding, and all should be placed back firmly so no malfunction will be caused by loose parts.
This Epiphone guitar arrived in the workshop with a damaged tone control. The repair is more difficult because the guitar is semi-hollow, and the wires are old.
After taking out all wires and components, the cause of the malfunction is simply a grounding wire broken off the potmeter. The potmeter is reconnected. The entire wire is controlled for badly soldered joints, or half-broken joints. Potmeters are controlled for scratching, and the output jack is controlled to give a solid connection.
The wire and components are placed back in the guitar. For this instrument all parts have to go back through the pickup cavity, a time consuming and tricky job.
The pickups are placed back, and the guitar gets a final check. Now the instrument is ready again for playing.