| Author | Message | ||
| cozmik_cowboy
Senior Member Username: cozmik_cowboy Post Number: 1679 Registered: 10-2006 |
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 .033µF 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 |
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 |
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 |
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 |
an easy one...make sure the strings are grounded! Tony | ||
| cozmik_cowboy
Senior Member Username: cozmik_cowboy Post Number: 1681 Registered: 10-2006 |
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 |
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 |
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 |
Oops! 2X post. (Message edited by Lbpesq on March 27, 2014) | ||
| lbpesq
Senior Member Username: lbpesq Post Number: 5699 Registered: 7-2004 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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. |
