Help me troubleshoot a pickup mystery?

Pickups, wiring schemes, switch techniques and onboard active electronics for guitars and basses
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sbanacho
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Post by sbanacho »

Hi,

I have a Tele with a problem that has plagued me for years, and never found a resolution. I thought I'd ask for help here where people are knowledgable about electronics.

The bridge pickup, without fail, goes completely silent. To get sound back, it requires that I poke at the circuit with a multimeter. As soon as I observe the connections with the multimeter (a) it always measures correctly (b) it begins working, usually for about a half hour, before it goes out again.

Again, the only thing that seems to temporary fix the circuit is applying a voltage across some of the circuit connections via the meter's connection checker. If I touch all the connections with my finger, no luck, but touching them with multimeter probes fixes it. Because of this, I've never determined what is causing the problem (because the multimeter always makes the problem go away). I never actually touch the pickup itself, only the wiring.

Over the course of the several years I've had this problem, I've done the following:
Resoldered every connection (multiple times)
Replaced both the bridge and neck pickup (ruling out pickup problems).
Replaced the switch (ruling out switch problem).
I've also changed both the bridge and the body, which would rule out those as culprits.

I would love to believe it was the bridge pickup itself, but what are the chances of two bridges of different makes having the same obscure problem? The only components that haven't changed are the pots, but I feel they must work as both pickups wire through the pots and the neck has never faltered.

Has anyone ever heard of such a thing? I would love to finally solve this mystery and fix the problem.

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lolbou
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Post by lolbou »

sbanacho wrote:Again, the only thing that seems to temporary fix the circuit is applying a voltage across some of the circuit connections via the meter's connection checker.
It actually delivers a -low- current. There's no voltage involved. :wink:

Did you try different amps?
sbanacho wrote:Replaced both the bridge and neck pickup (ruling out pickup problems).
sbanacho wrote: neck has never faltered.
Wow. these two gives serious :scratch: indeed...
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

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Post by Lucifer »

Interesting mystery !

It's possible that there's a break inside the insulation of one of the wires. You might be able to prove this by moving each wire when the circuit is working, to see if it stops working.
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lolbou
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Post by lolbou »

Lucifer wrote:It's possible that there's a break inside the insulation of one of the wires.
But the pickup ones are supposed to be new, and the neck one uses the same wires without any issue. :scratch:

What wiring do you use BTW?
- Are you a mod or a rocker?
- Uh, no, I'm a mocker.

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sbanacho
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Post by sbanacho »

lolbou wrote:
sbanacho wrote:Again, the only thing that seems to temporary fix the circuit is applying a voltage across some of the circuit connections via the meter's connection checker.
It actually delivers a -low- current. There's no voltage involved. :wink:

Did you try different amps?
If you count a smokey, then yes (it's the only other "amp" I have). I actually had another amp at the time this problem started, and so rule this out.

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sbanacho
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Post by sbanacho »

lolbou wrote:
What wiring do you use BTW?
I'll have to double-check next time I open it, but I'm pretty sure it's this standard wiring:
http://www.seymourduncan.com/support/wi ... ndard_tele

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sbanacho
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Post by sbanacho »

Lucifer wrote:Interesting mystery !

It's possible that there's a break inside the insulation of one of the wires. You might be able to prove this by moving each wire when the circuit is working, to see if it stops working.
I'll give it a try. Although it seems unlikely as I pretty sure I would have used new wire when I changed out the switch... but you never know. What makes me skeptical is what I previously mentioned: that touching parts with my fingers doesn't seem to help, only when the current is applied fixes it.

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Post by CHEEZOR »

Do you have a pic of your wiring? A wiring diagram along with that might also help. Is there any wiring that is attached to the bridge pickup which isn't attached to the neck? Did you swap out the switch? I don't see how it could be the switch, but it is the only thing I can think of right now that is isolated from the neck pickup in a tele. Try swapping sides on the switch (swap the connections for the neck and bridge pickups) and see if the issue occurs to the neck pickup instead. That may help isolate the issue a bit further.

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Post by karul »

sbanacho wrote:Replaced both the bridge and neck pickup (ruling out pickup problems).

I'm not following you here. You have installed new pickups?
sbanacho wrote:Replaced the switch (ruling out switch problem).

Same thing here. You have a new one ?


Remove the pickups from the circuit, then try to measure the resistance (measure it on the eyelets, not on the hookup wires). If you have nice, stable readings with appropriate (tele PUs) values, than the pickups are fine, problem is somewhere else. Also check the plate and magnets (continuity test), there should be no contact between the magnets and the plate. Check the PU with lens, look for anomalies.

Then check the complete wiring, carefully check the continuity on all wires. Check for cold solder joints.

If you still facing the same problem, than replace the bridge pick up.
If the problem is still there, then you have missed something.

If everything is OK, than you have issue with the pickup.
As someone already mentioned there's an insulation damage inside the coil of the PU. Could be the coil wire, too.

You can fix those things, too. But first things first. Locate the problem.

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Post by DrNomis »

Sounds like there's obviously an intermittent connection in the pickup, possibly where the wire ends of the coil are soldered to the leadout wires, what I think is happening is that there's just enough of a break in continuity to stop the flow of signal but as soon as you apply current from a multimeter the continuity is temporarily made...... :thumbsup
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Post by sbjkd »

Hi, I have done many Tele and Strat re-wiring/hot-dogging/Frankencastering during the past 20 years. This reminds me of a recent Strat mod repair, which used a push-pull knob to get a Tele sound from a Strat. It had the same problem as yours. It sounds like you have a soldering or a switch problem. This is how I fixed it.

1. De soldered the connection with the problem.
2. Cleaned off all solder from lug, including solder sucking/braiding to remove solder. Then, I used wet and dry paper (use anything from 120 to 240 grit) to clean up the lug so it was nice and clean. I also cleaned it with Isopropanol.
3. I removed excess solder from wires. Someone had used big gobs of solder.
4. I checked the PUP's output with a multimeter-no problem there.
5. Re-tinned the pickup wires and attached to lug, making sure that there was plenty of room-not solder all over the lug.
6. Re-sodered using minimum amount of solder, making sure that everything (solder joint) was neat, clean, and shiny at lug connection .
7. Measured PUP at solder joint.
8. After all of this, it worked perfectly.

Ensure that solder joints are clean, neat and shiny and not dull grey. You can go to the Fender forum and get wiring diagrams for all types of pickups and mods. You can buy a DVD called "How to Wire a Fender Guitar" from www.stewmac.com. Most people here are much more electronics savvy than me.
Good luck,
S

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Post by sbanacho »

Thanks to all the responses, I thought I'd give an update.

After this problem occurred again this weekend, I was able to verify that the connections between the base of the leads and the rest of the circuit were ok, so the problem must be internal to the coil, or between the base and the coil. I pulled the bridge pickup out (always a pain with Tele's), and there's no connection reading across the two leads (i.e. not a short, but no connection as in the ohm meter says "--"). I then reheated the solder where the coil and leads meet, and that didn't seem to fix anything. I think the pickup is pretty much now non-functioning.

As to some of your questions, maybe wasn't too clear in my original post, but at one point years ago I did swap out an entirely different pickup and had the same (or similar enough) problem, so I had always assumed it was elsewhere in the circuit. I couldn't believe the odds of having two bad pickups. But that was a while ago, and perhaps there was more than one problem.

Anyway, I'm going to chalk this up to a bad pickup(s), and order a new one, and hope I never have this issue again...

One last thing, the problem as I observed it is best described by DrNomis, who said the current from the multimeter could temporarily fix the continuity. How would that work? I had always suspected some kind of charge buildup causing the ground to be un-grounded, but wasn't sure if that's even possible, but it's the only way I could reconcile the observation that current fixed it (like current would somehow release the charge).

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Post by deltafred »

Thanks for the update, it's always nice to hear the outcome of these problems.
sbanacho wrote: One last thing, the problem as I observed it is best described by DrNomis, who said the current from the multimeter could temporarily fix the continuity. How would that work? I had always suspected some kind of charge buildup causing the ground to be un-grounded, but wasn't sure if that's even possible, but it's the only way I could reconcile the observation that current fixed it (like current would somehow release the charge).
The wire ends inside the pickup must still be touching but the copper will oxidise over time. A multimeter on the ohms range will apply a voltage across this oxide layer which is enough to break it down.

I have exactly the same problem with one of the speaker cables that run under my solid floor. One speaker will go off, crank the volume up and it comes back for a while. Its been like that for a few years and all the time I can get it back by tweaking the volume pot I am too lazy to pull another one through the duct.
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Post by fudgemarble »

has to be the pots
you changed everything but the pots
that's what it is.

could be a poor ground on the back of a pot, which is not the best way to ground anyway, either the cap leg isn't grounded, or the unused tab that people bend backwards to ground :slap: ...I just take the cap leg, put it through the unused tab, ground the leg to the pot and to the tab.

Sometimes you can get a short in the crowded tele control cavity that come sand goes, make sure all your ends are cut short, and no leads or any exposed wires are hanging around, when pushing all that crap back into the cavity stuff can touch and cause a short. Its hard to find out where because when you take the control cavity off everything isn't all jammed together any more=no short.

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