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cozmik_cowboy
Senior Member
Username: cozmik_cowboy

Post Number: 1679
Registered: 10-2006
Posted on Wednesday, March 26, 2014 - 10:17 am:   Edit Post

A query for some the more electronically literate here:

My beloved Epiphone Sheraton got damp in a flood in '96, which caused a slow but severe case of pot rot. This week I finally got around to making a new harness for it; CTS 9% 500K pots, Sozo Vintage Mustard .033F caps, Switchcraft switch & jack - all good, no? Well, no. Today, before installing it, I twisted the p/ups onto the pigtails I put in to facilitate said installation (and any future p/up changes) to do a tap test.
Through 2 different amps, with 2 different cords, I get no sound from tapping the p/ups - just a 60Hz hum that eases when I touch a pot or the jack and increases when I touch the switch. All wires go where they're supposed to, and all connections are strong (I just tested them). The only thing I'm not sure of - my wiring diagram from Seymour Duncan shows 1 ground lug on the switch, while my actual switch has 2. I wired across them, on the assumption that, as all the grounds tie together, that would work.

Any ideas?

Peter
lbpesq
Senior Member
Username: lbpesq

Post Number: 5695
Registered: 7-2004
Posted on Wednesday, March 26, 2014 - 11:21 am:   Edit Post

Peter:

Just some random trouble shooting thoughts. Have you tried bypassing volume and tone circuitry and just hooking the pickups directly to the amp to see if they work? If yes, then you might try adding just the volume, then just the tone circuit, etc., until you find the culprit. Or, I suspect you could trace it down with a multi-meter.

Bill, tgo
gtrguy
Senior Member
Username: gtrguy

Post Number: 727
Registered: 9-2004
Posted on Wednesday, March 26, 2014 - 12:08 pm:   Edit Post

Put an ohm meter on the hot and ground wire coming from each pickup and see what they read. Should be between 5k and 10k, I think.

Best of luck, I would love to see photos of the guitar!
cozmik_cowboy
Senior Member
Username: cozmik_cowboy

Post Number: 1680
Registered: 10-2006
Posted on Wednesday, March 26, 2014 - 2:35 pm:   Edit Post

Huh - thanks, Bill; I never would have thought of just sticking the p/ups to the amp; I'll give that a try.

I did meter them, David; 7.82 & 7.92.

And I forgot to add; on the little solid state Squier amp, it just hummed, but on the all-tube Silvertone touching pots made the reverb ping (I suspect that's down to the work the amp needs, though).

Peter
peoplechipper
Senior Member
Username: peoplechipper

Post Number: 402
Registered: 2-2009
Posted on Wednesday, March 26, 2014 - 10:17 pm:   Edit Post

an easy one...make sure the strings are grounded!

Tony
cozmik_cowboy
Senior Member
Username: cozmik_cowboy

Post Number: 1681
Registered: 10-2006
Posted on Thursday, March 27, 2014 - 9:04 pm:   Edit Post

The harness is still on the assembly jig (AKA manilla folder); as it's a semi-hollow with no back door, I wanted to test it before I installed. Would the lack of a string ground preclude sound from the p/ups?
Damn, there are times I wish I'd studied electronics instead of theater & history.......

Peter
lbpesq
Senior Member
Username: lbpesq

Post Number: 5697
Registered: 7-2004
Posted on Thursday, March 27, 2014 - 10:17 pm:   Edit Post

I can't imagine how one could cause the other. Even without any strings at all, you should still hear a tap or a vibrating tuning fork held over the pickup.

Bill, tgo
peoplechipper
Senior Member
Username: peoplechipper

Post Number: 404
Registered: 2-2009
Posted on Thursday, March 27, 2014 - 10:40 pm:   Edit Post

ground is important; ground that screwdriver then touch to the pickups and sound you will have...
lbpesq
Senior Member
Username: lbpesq

Post Number: 5698
Registered: 7-2004
Posted on Thursday, March 27, 2014 - 11:54 pm:   Edit Post

Oops! 2X post.

(Message edited by Lbpesq on March 27, 2014)
lbpesq
Senior Member
Username: lbpesq

Post Number: 5699
Registered: 7-2004
Posted on Thursday, March 27, 2014 - 11:55 pm:   Edit Post

Tony, are you saying that ungrounded strings will cause the electronics to cease functioning? In my experience, tapping an ungrounded screwdriver on the top of a pickup will result in a signal. Similarly, strike a tuning fork and hold it over a pickup and you will still get a signal without the tuning fork being grounded. I agree that proper grounding of the circuit is important, but Peter asked about ungrounded strings as a cause of total circuit failure. I just don't see how that could happen.

Bill, tgo
xlrogue6
Advanced Member
Username: xlrogue6

Post Number: 294
Registered: 8-2002
Posted on Friday, March 28, 2014 - 1:44 pm:   Edit Post

Bill is correct, lack of string ground will not kill the signal. If you're getting no signal, but a loud hum, your ground path is open somewhere. It's an easy error to make, especially if you're not experienced in wiring up instruments.
cozmik_cowboy
Senior Member
Username: cozmik_cowboy

Post Number: 1682
Registered: 10-2006
Posted on Friday, March 28, 2014 - 9:19 pm:   Edit Post

OK, I got it! My Seymour Duncan wiring diagram (and I think every other one I've seen) shows the switch as having one side with 3 lugs - bridge p/up-jack tip-neck p/up - and 1 ground lug on the opposite side. My actual Switchcraft jack has 2 lugs opposite the 3, so, as all the grounds are common, I tied across them.
Turns out the 3-lug side is neck-ground-bridge, and the 2-lug side is out to the tip.
60hz is gone (still buzzes too much, though), and tapping gets sound - which reacts appropriately to switch, vols & tones.
Busy tomorrow, so Sunday or Monday I put her back together.

Peter
cozmik_cowboy
Senior Member
Username: cozmik_cowboy

Post Number: 1683
Registered: 10-2006
Posted on Wednesday, April 02, 2014 - 10:15 am:   Edit Post

Well, after 4 hours of trying to find the angle at which the pots will fit through the f-hole (I'm assured they will), I have had to step back for a while, as I caught myself reaching for a hammer; I swear, this will be the last semi-hollow I ever rewire!!

Peter
gtrguy
Senior Member
Username: gtrguy

Post Number: 732
Registered: 9-2004
Posted on Wednesday, April 02, 2014 - 10:29 am:   Edit Post

Ah, yes, I have spent countless hours trying to stick wiring into hollow body thinlines! It halps to run a small wire through the output jack and use that to pull the harness to where it will go after getting that wire dressed out the hole for it in the guitar. I also use surgical hemostats to grab pots by the shaft when inside the guitar. You can also use a flat blade screwdriver and push it into the slot usually on top of the shaft of those pots and weasel them up into their holes. Be sure to slip the nuts and washers on the screwdriver shaft first.

Fun stuff!!!
jzstephan
Advanced Member
Username: jzstephan

Post Number: 247
Registered: 1-2012
Posted on Wednesday, April 02, 2014 - 4:58 pm:   Edit Post

http://youtu.be/6UyR7aVQRKg

How I Remounted Pots In My Epi Dot- video

it happens real fast, but it will help.
cozmik_cowboy
Senior Member
Username: cozmik_cowboy

Post Number: 1685
Registered: 10-2006
Posted on Wednesday, April 02, 2014 - 9:44 pm:   Edit Post

My problem isn't getting them back up through the mounting holes, it's getting them - full-sized, not mini-pots, as in the vid John so kindly linked - down through the f-holes into the body. I'm about to give up & order minis, but I really wanted to use full-sized; I mean, c'mon, they've made semi-hollows longer than they've made mini-pots, haven't they? Anyone here from Kalamazoo to give me the secret?

Peter
davehouck
Moderator
Username: davehouck

Post Number: 11312
Registered: 5-2002
Posted on Thursday, April 03, 2014 - 4:31 pm:   Edit Post

This guy replaced the pots in his Epiphone, and he has several videos about the process. But there's no mention of full-size verses mini; so probably no help.

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