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Bridge Grounding

 
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Wombat



Joined: 01 Sep 2012
Posts: 891

PostPosted: Mon Sep 07, 2015 3:42 pm    Post subject: Bridge Grounding Reply with quote

I've got a bridge grounding issue on a guitar with an adjustable bridge. The guitar was described as "flaky", and with a bit of hunting around with an ohm meter, it appears that while the ground from the pots to the socket for the bridge is solid, the post in the socket is loose unless it is screwed down tight so the bridge is at its lowest height.

If the bridge is raised at all, the string tension is (surprisingly) not enough to maintain contact between the threads on the bridge post and the socket, and the ground from bridge to pots becomes intermittent. (The bridge is seated solidly, I can't detect any movement, the guitar stays in tune quite well, so it's not moving about ... it's just that the electrical connection from bridge and post to socket and grounding wire is intermittent unless the bridge is tightened all the way down).

Pulling the sockets and replacing the entire bridge is a possibility, of course ... but I'd rather not do that if it isn't necessary. Anyone have this problem before, and would threading in some conductive tape when seating the post into the socket be a reliable fix?

It's not my guitar, and while I don't want to pass on the expense of replacing the bridge if this isn't necessary, I don't want to perform a half-assed repair that won't be reliable either.

Thoughts on this?
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marksound



Joined: 15 Aug 2005
Posts: 16669
Location: OKUSA

PostPosted: Mon Sep 07, 2015 4:01 pm    Post subject: Reply with quote

Assuming it's a TOM bridge/tailpiece? Given that I've only ever built one guitar like this ...

The wire is in the tailpiece stud hole, right?

First, I'd give the ground wire a tug. If it comes out of the hole, there's your problem. If it's tight, pull the insert and see where the wire is. It might not be stripped back far enough and the insulation is what's holding it in place.

You could solder a small washer on the ground wire so it seats in the hole and the stud insert will make solid contact.

Just some thoughts off the top of my head.
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Wombat



Joined: 01 Sep 2012
Posts: 891

PostPosted: Mon Sep 07, 2015 4:31 pm    Post subject: Reply with quote

The ground wire has a solid ground to the threaded socket. It's not loose at all, and it's steady on the meter. The problem is that when the post is threaded down into the socket, it has solid, reliable ground only when threaded all the way down tight. If the post is raised, its threads are rather loose in the socket, and the ground becomes intermittent.

I would think the string tension on the bridge would be enough to push the post so that its threads maintain contact with the socket, but that is not the case. If I lower the bridge as far as it can go, ground is perfect. If I raise it, ground is mostly there, but begins to cut out. Never came across an adjustable bridge with threads this loose / coarse before.

If it was mine, I'd try some copper tape around the threads, but its not mine, and I don't want to make an unreliable repair.

Also - the socket is not a hollow tube - it is capped at the end. The post is entirely contained inside the socket, so there's no way for the post to reach the ground wire. The ground is to the outside of the socket, and it is tight and meter shows consistent ground between the socket and the ground connection at the potentiometer.
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Mr. Clevername



Joined: 08 Dec 2006
Posts: 2450
Location: San Francisco, CA

PostPosted: Tue Sep 08, 2015 10:07 am    Post subject: Reply with quote

I don't see why some kind of conductive metal foil wrapped around the post would be unreliable. Or maybe you could wrap some very fine wire around the threads, put a drop of CA on it(?).
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Action-Cashin



Joined: 28 Nov 2005
Posts: 1521
Location: Austin, TX

PostPosted: Tue Sep 08, 2015 10:49 am    Post subject: Reply with quote

Possible contamination inside the hole and or the post?
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Wombat



Joined: 01 Sep 2012
Posts: 891

PostPosted: Tue Sep 08, 2015 5:54 pm    Post subject: Reply with quote

Contamination / corrosion might be an issue. I did try cleaning it out with an old toothbrush, but it doesn't really get in there well. I should find a wire bore brush of the right size in the gun cleaning box and try that before I get creative ...

Thanks for the tip!
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