Epiphone Ultra 339 Problems

So I've had a mate drop one of his guitars around to see if I can fix an issue with it. I've previously done a setup on it and it is an interesting bit of kit.

For those unfamiliar it's one of these:

https://www.premierguitar.com/articl..._Guitar_Review

So one of the features on this guitar is a Nano Mag pickup which occupies the last fret on the fret board. There is a switch in what is normally the rear pickup tone control that lets you swap between normal humbuckers, the Nano Mag or both.

For some reason only the nano mag pickup is currently working. So you get sound when it is selected or both it and the humbuckers but not the humbuckers on their own. My immediate though is that it's the switch or maybe the volume pots which are the problem - the volume pot shafts appear to be bent and they are very loose when you turn them. Diagnosis is somewhat hampered by everything being on a printed circuit board, so I'm a little apprehensive about just swapping things out and seeing what works.

A bit of a google reveals a raft of problems with these guitars from the factory. So much that it's difficult to track down anyone else who's had this particular problem.

I'm going to keep researching, but I thought it was worth throwing out to the brains trust here.

Does anyone have any experience with these things or any thoughts on the best diagnosis work flow?

After work I'm going the get out the multi meter and see what I can see. So feel free to fire away with advice and opinions :)

Some pics for attention.

https://i.imgur.com/w2IQ2l6.jpg

https://i.imgur.com/2N1u4sA.jpg

No experience with that guitar, but a multimeter reading resistance (with 500k pots if it's not autoranging then you'll probably need the 2M ohm setting) across the volume pot connections (centre tab and either of the outer tabs) should indicate if the wiper is making contact with the track all the way around.

Yep that's the first thing I'll be looking at this afternoon. I've ascertained that the switch in the knob for selecting nano-mag/humbuckers is working - there are indicator LED's on the bridge humbucker that show what 'mode' it is in and they are at least illuminating for what should be humbuckers only.

Had a lull so I went over the pots and switches with the mulitmeter and they all checked out OK. Decided to check all the earths and found this on the stereo jack:

https://i.imgur.com/9m7lj7p.jpg

The yellow wire is disconnected as well. They are stupidly tiny and fragile. Anyway, soldered it back up and presto, shes back in working order.

Glad I didn't have to mess about with the PCB.

Hurrah! It's nice when it's something relatively easy to trace and fix.

Yep. I was a bit concerned when I saw the insides, glad it was an easy fix. I’ve been playing it this evening. It’s quite a nice guitar. Can’t say I’m a big fan of the nano mag pick up- reminds me of the Alumitones. It’s just missing something. It does fatten the sound overall when used with the humbuckers, but I can take or leave it. It’s also one of the first hollow bodies I’ve played where the size didn’t annoy me. It’s a nice weight too.

Very pretty looking guitar.

That PCB is a daunting proposition. Glad it was an easy fix