Pickup question

THX1136

THX1136

Bonehead
I recently did some research here for pickup info. My son bought a Epiphone G310 SG and the bridge pickup lost considerable level. I found what I needed to know here on checking it to find the cause. His turns out to be a shorted pickup - very low impedance when checked. One thing I did not come across was how this happens to a pickup. The reason I ask is because he asked and I did not know.

The only thing the guitar has been through that negatively impacted it was a broken neck due to an unfortunate accident - my wife fell into the guitar when it was leaning against the wall.

Anyway, can someone enlighten me on this? Thanks in advance for your time.
 
are you sure it is the pickup and not the volume pot? aparently the accident that caused the broke neck also damaged something in the electronics as well.
 
The coils of factory pickups are wound at high speed using very thin wire. If the tension adjustment is only slightly too tight the wire will be under more stress than it should be. Copper is a very flexible but it can become brittle when it bends. A pickup can fail simply from internal stresses overcoming the capacity of the wire to remain intact. An external shock is not necessary. It is surprising to me how rarely this happens given how many pickups are out there. Still, People who work on guitars will see it from time to time. I actually see it less often than I used to.

As Roguetitan pointed out, there are other (more likely) problems that can cause you to lose pickup output in a circuit. I did not see your prior thread on this, so I don't know how you got to your diagnosis. I hope the above answers your question anyway.
 
I searched the forum for information on how to check the pickup itself with a VOM. I forget the individual that provided the info in the thread I looked at, but basically what was said was a break in the coil would test as an open circuit; shorted coil would test at very low impedance and a good one would test at a high impedance (13K or higher depending). It tested out at a very low impedance - .884K. I did see the info on checking the pots also which I had thought to do. Since you have mentioned there are other more likely causes I will check the pot out too.

The accident left the body looking unscathed. None of the pots seem to be physically damaged - they still turn smoothly without noise. The neck was pulled at the joint with the body causing some minor splintering. I figured drilling the holes out a bit, gluing in dowels, and redrilling for the mounting screws would be the fix. The luthier I took the guitar to did basically that (only better than I would have done). The guitar appeared fine after getting it back from the shop. The pickup lost "volume" within the last couple of weeks. The neck repair was done last fall.

Are there any other things I should be looking for electronic wise? Thank you both for your responses.
 
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THX1136 said:
Are there any other things I should be looking for electronic wise? Thank you both for your responses.
Click to expand...
Process of elemination...
bad wiring connections bad solder joint bad connection at the plug.

if the bridge pup works you know it is not the plug, check the wiring going from the pots to the pickup to make sure they are connected so on and so forth...

if you do have to replace a pickup go ahead and replace the pots as well
the pots are inexpensive and just helps to eleminate the chance of having to do it later on.:)
 
More of an update than anything else. I CAREFULLY rechecked the guitar. To recount - the neck pickup works fine, bridge has greatly reduced output. To match the output of the bridge relative to the neck the neck pickup volume must be set at "2" with the bridge full up.

The pot for the bridge pickup measured 520K - marked as 500K on cover. With leads on middle lug and one outside I get a smooth transition from 520 to .002 and back - no bumps, loss or other wackiness.

Measuring the pickup again I get a reading of 92xx (obviously I did a poor job the first time I measured). I resoldered all connections to the pot - physically removed and resoldered. No improvement in output. I haven't tried just connecting the pickup lead directly to a cord into an amp (obvious next step to try) - maybe tomorrow.
 
THX1136 said:
More of an update than anything else. I CAREFULLY rechecked the guitar. To recount - the neck pickup works fine, bridge has greatly reduced output. To match the output of the bridge relative to the neck the neck pickup volume must be set at "2" with the bridge full up.
Click to expand...



Sure sounds like a bad pickup to me.


Light

"Cowards can never be moral."
M.K. Gandhi
 
Yeah, sounds like your pick-up bit the dust. The wire used for the winding is about as thick as a hair. It's got a coating on it to keep it from conducting (otherwise all you would have is a oval blob of copper). If the wire conducts through the coating anywhere on the thousands of winds on the coil, it's done. It stinks but it does happen. I had a Dimarzio S. dist. in my guitar for years that worked fine gig after gig. Then one night I take it out of the case and ...nothing from one p-up. Same situation, disconnected the wires from the pot and measured it. It was shorted inside the coils.
 
yep... looks like the pickup is garbage...
it sounds as though you pretty much know what you are doing so replacing a pickup should not be much of a problem for you.:)
 
Milnoque said:
The coils of factory pickups are wound at high speed using very thin wire. If the tension adjustment is only slightly too tight the wire will be under more stress than it should be. Copper is a very flexible but it can become brittle when it bends. A pickup can fail simply from internal stresses overcoming the capacity of the wire to remain intact. An external shock is not necessary. It is surprising to me how rarely this happens given how many pickups are out there. Still, People who work on guitars will see it from time to time. I actually see it less often than I used to.

As Roguetitan pointed out, there are other (more likely) problems that can cause you to lose pickup output in a circuit. I did not see your prior thread on this, so I don't know how you got to your diagnosis. I hope the above answers your question anyway.
Click to expand...

A good post. Just to add to it, I can see how this could happen - heat, afterall, causes expansion, so it's quite feasible that an already stressed wire was heated a little too much, causing its bulk to expand, and push the tension in the wire of the outer-layer of the pickup coil to breaking point. Which is quite cool, if you think about it. Means the dude could be such a hot guitarist that he made his guitar burst. And that deserves bragging rights.
 
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