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Strange wiring problem

Monroe

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Mar 11, 2008
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1,139
I have wired many many guitars and am competent at soldering.
But this one has me stumped:
A late 70s SG that I rewired/upgraded almost a year ago has developed a weird problem all of a sudden.
As always, I used the 50's diagram posted here on the forum.
All of a sudden, neither volume pot will take the guitar to total silence.
With either (or both) pots on zero, a considerable amount of sound still there. Like volume on 2-3.
Doesn't matter which switch position. Works as it should except for that.

After a visual inspection that turned up nothing obvious, I gutted it and checked all the components, all OK.
Vintage taper CTS pots ranging from 484K (bridge vol) to 521K (neck vol) and vintage wind Fralins. NOS PIO Russian caps.
I didn't meter the caps, but the tone controls work nomally. With tones out of circuit the problem remains.
Gutted and rewired twice today, same issue. Has anyone seen this?
Next I think I'll try wiring it junior style (one pickup, no switch, etc) to try and isolate it.
What am I overlooking? This started up all of a sudden after working perfectly for nearly a year.
Thanks!
 
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PaulD

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Jun 25, 2007
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I would check all your ground connections, when the volume pot is on zero the signal is shorted to ground, a dodgy solder joint could be causing a resistance to ground somewhere that would have the effect you describe.
 

thejaf

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I doubt the wiring changed. Look at the output jack and cable, as those get used/movement while the wiring doesn't.
 

PaulD

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I doubt the wiring changed. Look at the output jack and cable, as those get used/movement while the wiring doesn't.

Bad or loose connections at the jack socket or cable would not cause the symptoms the OP described, they would cause the signal to cut out intermittently or no signal at all.
 

Monroe

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The chance that the owner's cable(s) and my test cable would cause the same problem is pretty slim.
It's strange that the symptoms are the same for both pickups and in any switch position.
The only components in common to both pickups are the switch and the jack...
And, and PaulD observes, a bad jack connection would cause drop-outs or no sound (and maybe crackling)

The more I stew over it, the more I lean toward switch rather than jack.
But the way this problem started all of a sudden after working correctly for many months has me baffled.

Will gut it for a third time today and try wiring it with just one pickup and one volume pot.
If it's a pickup or pot, that will isolate it. If that works, I'll add the tone circuit.
If both pickups work singly, with and without tone pots, it kinda has to be the switch...
 

thejaf

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If there is a bad connection to signal ground (when guitar signal hits the amp), then there won't be adequate ground reference. The volume pot would be simply adding resistance in series to the signal, reducing it some and rolling off some treble (a simple low pass filter).

Test continuity between guitar ground and the amp chassis
 

Monroe

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If there is a bad connection to signal ground (when guitar signal hits the amp), then there won't be adequate ground reference. The volume pot would be simply adding resistance in series to the signal, reducing it some and rolling off some treble (a simple low pass filter).

Test continuity between guitar ground and the amp chassis

The choice of amp (or cable) doesn't alter the symptoms.
It happened at the owner's home with his amp.
It happens here at my place on my amp(s) as well.
But you're right, it does seem to be some kind of faulty connection.
 

Monroe

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So I tried wiring one pickup at a time w/ just a vol pot... (EVH style) no problems.
When each worked with just the above, I added the tone pot/cap... (Jr style) no problems.
I even went ahead and wired both pickup circuits in parallel minus the switch.
That worked as if the switch was set to the middle pos.
Pretty sure it was the switch at this point. Put the switch back in to reconfirm............
And it is now working correctly. So I have a working guitar, but no answers.
I mean, it had to be a ground issue of some kind, but who knows.
After re-doing it as many times as I have in the last few days, I'm just glad I'm done.
If he brings it back again I'll replace the switch.
 

PaulD

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Glad to hear you have sorted it. It's annoying when you don't find a definite cause - there is always that nagging doubt that the problem will reappear! I can't think of any way that a fault with the switch would cause the problem you described but who knows, those pesky electrons do seem to have a knack for doing things you don't expect!
 

thejaf

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If I had to guess, it'd be a cold solder joint on the ground at either the switch or output jack. The act of reflowing those connections fixed the issue :salude
 

PaulD

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If I had to guess, it'd be a cold solder joint on the ground at either the switch or output jack. The act of reflowing those connections fixed the issue :salude

A bad ground at the switch would not cause the problem, the switch ground connection just grounds the metal body of the switch to prevent it picking up RF interference, a high resistance ground connection at the jack could have caused the problem.

EDIT: Thinking about this again the switch ground connection could potentially cause the problem depending on how it was wired, if, as is often the case, the shielded wire from the jack socket ran directly to the switch without being soldered to the back of a pot then the connection at the switch would be in the signal path and could have been the cause. However as it had been re-soldered several times it seems unlikely.
 
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Monroe

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Mar 11, 2008
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Plus I completely disassembled all the components multiple times.
And have been soldering since my pre-teens.
And retired in 2012 from a job where I soldered things on a daily basis.
I can't visualize how the switch would have caused the symptoms.
And I am dubious that it was in fact the switch at all.
To me, it seems more likely that there was a ground connection problem with the leg of the vol pot that connects to the pot case.
But the fact that it was exactly the same on both pickups, singly or in tandem, that had me expecting to find something else.
Anyway, thanks to all that helped me brainstorm it.
 
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