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Mustang Electrics Problem

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Mustang Electrics Problem

Postby JRC1 » Wed Dec 06, 2017 6:31 pm

Hi - I have a problem with my Mustang. I thought it was just the input jack, however, I am not entirely sure if it is and before I start messing around with it too much I want to ask some advice and see if I was correct.
Here is a link to a YouTube video which shows there's a hum when anything metal is touched on the guitar. There is some output when pickups are selected but it's not great.
https://youtu.be/y4DrumYTspg
Thanks in advance for any advice you can offer to diagnosing the problem. is it the pick up selectors, the pick ups themselves?
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Re: Mustang Electrics Problem

Postby zenguitar » Wed Dec 06, 2017 8:10 pm

Swapping the signal and ground wires on the output socket can result in issues like this. Also, if the socket has come loose and been twisted there could be contact between the signal and ground wires.

Best to open it up and have a good lock at the condition of the wiring.

Andy :beamup:
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Re: Mustang Electrics Problem

Postby Wonks » Wed Dec 06, 2017 8:58 pm

Is is any of the metal surfaces or is it the strings+bridge+tremplate? The ground wire for the bridge (or the trem - not sure where Fender connect the ground wire on these) may have come loose. Touching the strings mat then allow any noise picked up by your body to pass to the strings and then to the pickups. When the strings are grounded, then touching them normally reduces any hum.

Have you done anything to the guitar, after which it started buzzing? I know people sometimes use a bit of plastic tube on the bridge posts to stop the bridge wobbling about so much. If so, and it is the bridge that's grounded, the tube(s) may be stopping the bridge from touching the body inserts. In that case, the plastic probably just need trimming back at the bottom so that metal can touch metal.

It also looks like there's no dedicated ground wire from the jack socket to the back of the pots, and ground continuity relies on a good contact between the pots and the metal control plate. The pot and jack nuts can come loose over time, so it's a quick job to remove the knobs (just ease them up a bit at a time with a flat bladed screwdriver or even a spoon), turning the knob a bit each time. Then get some spanners (typically between 10mm and 13mm) and tighten up the nuts for the pots and the jack socket again.

Ideally you'd use a multimeter to check the resistance. Put it on the lowest ohm setting, and you should be registering less than an ohm between the pot backs themselves and between the pot backs and the centre part of the jack socket (not the tip connection). You should also be getting a similar reading between the bridge and trem plate and the centre part of the jack socket. Any high readings (which in this case I'd say would be anything over a couple of ohms) and the connections aren't as good as they should be. You might then need to take the jack and pots off the plate, rub the connecting areas down with some fine sandpaper, spray with some switch cleaner, and re-assemble.

Also, it's hard to tell from the video, but is the tone pot's capacitor connected at both ends? One end looks to be soldered to the correct tab on the tone pot, and the other should be soldered to the pot's casing. I can see a blob of solder in the middle of the pot, but it's not clear if the other capacitor leg is run to there (or possibly somewhere else on the pot's body). If it's come loose, then it needs re-soldering back on. I'm not sure if that could cause the hum, but it certainly means your tone control won't work until it is.
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Re: Mustang Electrics Problem

Postby Longsight John » Thu Dec 07, 2017 9:31 pm

Process of elimination required mate.
First, try your setup with another guitar to eliminate the amp and your cable as culprits.
Then.. Ah.. It's your jack. It always is usually.
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Re: Mustang Electrics Problem

Postby Wonks » Thu Dec 07, 2017 10:33 pm

I had something vaguely similar today when checking out a Laney powered monitor for a friend. I had the plastic knobs off the controls, and it hummed when I touched the treble control pot shaft. Not the volume, mid, or bass controls, just the treble. Something not 100% right with the grounding of the pot, so tomorrow it will be looked at in more detail. (for some reason I totally overlooked the four big bolts holding the electronics module in on the side until it was too late).
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