Jaguar bridge pickup shorting when lowered into cavity

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thebailiff
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Jaguar bridge pickup shorting when lowered into cavity

Post by thebailiff » Sun Oct 17, 2021 4:21 pm

Hi all,

I have a recently-acquired Squier Vintage Modified Jag, and I am almost done rewiring it to American Professional Jag routing (https://www.fmicassets.com/Damroot/Orig ... 7-2016.pdf). The problem is when I select anything with the phase switch in the "on" position, the bridge pickup goes silent (a SD S-JAG2b). Upon further inspection, the leads on the DPDT switch on the upper horn are all in contact with each other when the switch is set to "on". Since the bridge pickup is the only one wired directly to the DPDT, I am guessing there is a short going to the ground circuit somewhere.

But, when the bridge pickup is taken out of the housing cavity, the switch contacts behave as normal. It is only when the pup is seated low enough that the connection goes bad. I tried putting foam under/over all the metal points I could find (including a body ground lug right underneath the pickup housing) and it still won't drop low enough without shorting. Is there a bad wire in there? Can't imagine pinching it would cause a short - the outer shielding looks okay on both leads.

I'd appreciate some expertise. I am at wits end here being so close to finishing. Also bear with me if I have any inconsistencies as I have been away from electronics for some time.

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Embenny
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Re: Jaguar bridge pickup shorting when lowered into cavity

Post by Embenny » Sun Oct 17, 2021 4:31 pm

The issue is that your claw is soldered to the "coil start" terminal of the pickup, which are both normally connected to ground. When you reverse phase, it's pitting the claw into the signal path because coil start and coil end leads are being reversed. When you bottom out the pickup, the claw is making contact with the shielding paint or lug in the cavity, which is connected to ground, and is now shunting signal to ground.

The solution is to desolder the pickup claw from the coil start, and run a separate ground wire from the claw. That way, the two coil leads can be reversed without putting the claw into the signal path.
The artist formerly known as mbene085.

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thebailiff
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Re: Jaguar bridge pickup shorting when lowered into cavity

Post by thebailiff » Sun Oct 17, 2021 4:45 pm

That makes perfect sense. I actually forwent the green wires in that diagram because I didn't know what they meant! The "extra" bare wire from the Hot Jaguar pickup was actually not soldered but just pushed up against the claw when seated, like you describe. Going to try the extra wiring now.

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Re: Jaguar bridge pickup shorting when lowered into cavity

Post by thebailiff » Sun Oct 17, 2021 5:26 pm

Update: After running ground wires from each pup claw, the meter still shows continuity when the bridge pickup is seated in. Did I just need to ground the bridge claw? I ran wires for both. Or should I just snip the extra coil tail altogether (right now it's curled up under the foam)?

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Re: Jaguar bridge pickup shorting when lowered into cavity

Post by timtam » Sun Oct 17, 2021 6:03 pm

As mbene085 said, a jag pickup that is having its phase flipped should look like the top pic below: separate wires for the coil ground (going to the phase switch) and the claw ground (which should be permanently grounded).

That also applies to a pickup in a series switching scheme, that is having its ground connected to another's hot. The Am Pro schematic (bottom pic below) has both phase and series circuits, so both pickups must have separate claw and coil grounds.

The little jumper that normally joins the claw and coil grounds (as in the middle pic) must be cut when adding the new ground wire. If your pickup cavities are shielded, also make sure that the hot cannot contact the (grounded) shielding. I also put heatshrink over the switch terminals so that shorts cannot occur there when everything is crammed into the switch cavity.

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"I just knew I wanted to make a sound that was the complete opposite of a Les Paul, and that’s pretty much a Jaguar." Rowland S. Howard.

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thebailiff
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Re: Jaguar bridge pickup shorting when lowered into cavity

Post by thebailiff » Sun Oct 31, 2021 10:06 am

Hey guys,

After finally getting more time to sit down with this project, I still cannot get the pups to stop shorting out. I soldered ground wires underneath the foam, snipped the extra ground leads, put painters tape over the little solder joints on the ends, and it still shows continuity on all parts of the phase switch when lowered down to a satisfactory level in the cavity.

Notably, the shorting now happens when the phase switch is both on and off. It goes away when one or both pickups are raised enough out of their cavities. Does the Squier VM Jag have shielding paint on the insides? I really don't know what else could be causing this. Body ground lugs under each pup?

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Re: Jaguar bridge pickup shorting when lowered into cavity

Post by thebailiff » Sun Oct 31, 2021 12:12 pm

What I ended up doing was putting painters tape all over the walls and floor of one of the pickup cavities. Something must have been touching the ground lug or shielding paint that wasn't supposed to. It works now, so it'll do. Thanks for your help!

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