A wiring puzzle

[crossroads46]

I have a real wiring puzzle. I have a Switch Midi guitar that has 2 Wilkerson humbuckers and a 3-way switch, one volume and one tone knob (besides all the midi wiring) My tone pot is gone. When I first started using the guitar it was only as midi but I sold my synth. The first thing I discovered was no ground to my guitar jack plate. I re-soldered the ground (Black spliced with white then continuing as black) wire and it was ok. The soldering on this guitar is a mess. My wires are Blue and Red with Black being the wire connecting the volume and tone pots. The capacitor seems to be wired right on the tone pot but then there is a thin white wire (the same as the many ones on my 3 way switch and this wire is soldered from the center lug to the back of the tone pot. When I looked at it for the first time because of crackling when I turned the knob, it appeared that this white wire and a black (I think it is ground) were soldered together on the back of the pot. After losing sound and increased crackle I added solder to the two onto the back of the pot and now I have NO sound. It seems to me that this small white wire is in effect shorting the tone pot out. I want to replace the tone pot but the wrong does not seem conventional especially this small white wire from lug to ground. The basic Duncan diagram is similar but their green is my blue and my black is ground?
Also upon replacing the pot I am confused as to the size of the capacitor some say 22 mf and some say 47 mf. Which do I buy? Switch is out of business so I can’t ask them.

 

[DrNewcenstein]

Re: A wiring puzzle

Wow, Switch are already dead? Didn't think they'd be around long with those designs and materials, but still...

Anyway, this Tone pot wire - it connects the center lug of the tone pot to the back of the tone pot? Where's the capacitor wired?

I've seen capacitors wired to the pot casing as well as connecting the two pots, and also spliced with extra wire, so either way would be correct, however, it sounds like you've got an extra (not for the cap) wire on the Tone pot, and that's shorting it to ground?

If the Tone pot is wired so the outer lug has the capacitor and the other end of the cap is wired to the pot casing, then the white wire in the center lug should go to the volume pot.


22 vs 47, yet another "eternal argument" - get both and wire them to a push-pull so you can select between them

 

[crossroads46]

Re: A wiring puzzle

The capacitpr IS wired to the outer lug of the pot and then to the pot casing. The white wire is soldered to the center lug but is only as long as the pot is deep, 3/4" at most and never was connected to the volume pot and all worked. There are 12 to 15 white wires on the volume pot already (mostly midi I assume and I wanted to replace that too but could never unravel the spagetti of white wires.) If I were to run a new white wire between the pots I have no idea where except from the center lug of the tone to the casing on the volume? Is this a bad idea? This was a good guitar for midi and cheaper than a gK2A roland pickup and I really have no use for it but want to get it working for practice, to sell, etc. Thanks for replying so quickly. I think I am going to remove this one white wire and see what happens.

 

[crossroads46]

Re: A wiring puzzle

I disconnected the white wire. nothing. I tried connecting to ground. Nothing. I tried connecting it to the volume pot. Nothing. Maybe the tone pot and/or the capacitor is burned out. I even tried bypassing the tone pot, still nothing. All I can think of at this point is to start from scratch with new tone and volume pots and wire them as they are supposed to be. I will extensively photgraph the midi connection but leave them disconnected to get this thing working OR sell the parts: pickups, Grover tuners, etc.

 

[DrNewcenstein]

Re: A wiring puzzle

Sounds to me like the pickups go through the MIDI connections? Like maybe just using their connections as a pipeline for the signal, not really being dependent on the actual MIDI signal.

I'd say the bundle of whites on the volume pot were for the MIDI bridge saddles. I'd isolate the pickup wires from those and have nothing but the pickups connected to the volume pot.

Is it a standard 500K pot with a switch on it, or is it a multi-position thing like the selector on a Variax? If it's a standard 500K pot, then put the volume and tone together according to any standard diagram, but if it's a multi-position selector like the Variax, then either replace it with a standard 500K pot or spend some time looking for the connections that match (a bag of jumper clips comes in handy right about now).

Anyhoo, running a wire from the center lug of the tone to the volume pot casing will ground out the tone control. You'd want to run it to one of the prongs on the volume pot.

 

[crossroads46]

Re: A wiring puzzle

It's a standard 500k pot. But what really baffles me is that everything worked until this big blob of solder broke loose from the base of the tone pot case. Believe me the solder is a mess in this guitar as if it was used as a practice guitar for a soldering class. And what was connected to this mess of solder was a black wire that could either be ground or hot because it seems the black from the pickups is hot and the ground from the output is black; and a white wire from the center lug of the pot. I want to try to buy new pots and disconnect all the midi like you suggest. Maybe the tone pot is dead now but still there is no logic that I can see to the way it was wired.

 

[crossroads46]

Re: A wiring puzzle

I would like to thank everyone that responded to my question. Today I took the guitar to the best Luthier I know. It took him about fifteen minutes but he agreed that the wire that was soldered to the center lug of the tone pot SHOULD be wired to the center lug of the volume pot much as we all decided. After thinking that was the fix he tried plugging in the guitar and NOTHING. He removed the volume pot and checked it for a signal. He got one from Midi but NOTHING from the guitar circuit. He concluded that besides wiring the tone and volume pots together that the HOT and GROUND to the volume pot were both shorted. Both pots were OK. Go figure, the trouble started and happened with the tone pot and the volume pot wiring was the culprit. So in short, the midi circuit is fine and he is going to completely rewire the output to the tone and volume pots CORRECTLY at an extremely reasonable price. So I left it with him to do so.