Official Luthiers Forum!

Hello everybody.
I have a bass of a friend of mine. It's a Fender Jazz Bass, American, I'm not sure about the model.
Anyway, the neck pickup is mute, just the bridge pickup sounds. Measuring the resistance from the output: the bridge pickup is 6.7k, the neck (not working) pickup about 111k. If I put in parallel the neck pickup with the bridge pickup the resistance rise up until 111k.
The wiring under the plate is ok.
I extracted from the bass the neck pickup, took off the cover, at a first sight it seems ok. I desoldered it, and the resistance between the two black wires and the white wire is 0 Ohm.
I'm wondering what's wrong with this pickup and if I can fix it.
Thanks.

If the resistance of the pickup is super high when wired into the circuit but zero out of the circuit I would suspect there is a short in the pickup. The 0 ohms indicates the short, 111k you are reading when the pickup is in the circuit could be an artifact of some other part of the guitar circuit, like a potentiometer.

As for how to fix it - is there any visible contamination that would short the coil? I’ve seen steel wool fragments get under a pickup cover and cause this. This is why steel wool is banned from my shop.

Thanks.

I want to change a bit the situation. I don't know if I make some confusion, but that's it:
Both the pickup wired, Volume neck at 10 and Volume bridge at 10: resistance between tip and ground is 6.7k.
Both the pickup wired, Volume neck at 0 and Volume bridge at 10: resistance between tip and ground is 6.7k.
Both the pickup wired, Volume neck at 10 and Volume bridge at 0: resistance between tip and ground is 111k.
Both the pickup wired, Volume neck at 0 and Volume bridge at 0: resistance between tip and ground is 111k.
No difference if I leave out the neck pickup.

The neck pickup stand alone measures 0 Ohm. If I connect it with test leads at a jack and directly in the amp I got no response if I hit the poles with a screwdriver.

I couldn't see anything weird or wrong in the neck pickup. I had took off the cover, but it still measured 0 Ohm.

0 ohms is infinite resistance, you have a broken wire somewhere.

_________________
Jim Watts
http://jameswattsguitars.com

And this does happen occasionally with no known cause.

A common way to kill a pick-up too is steel wool on the fret board which is of course metal and the shavings short the windings on the pup. I use steel wool to clean frets but I completely mask the pups and then vacuum before removing the tape.

We have a client who paid $2,000 for an original PAF that had one side with a shorted wire and no known cause hence the lower price for an original PAF. It was rewound by an expert in original PAFs and sold at reduced price. We installed it and adjusted it to play nice with the bridge pup.

On meters I’m familiar with, 0 means there is continuity, not infinite resistance, so I would take that to mean there is not a broken wire. There’s a short between testing points, as you are reading very low resistance, indicating the pickup coil you are expecting to read is being largely bypassed.

Infinite resistance is usually indicated some other way, either by “INF”, or “- -.- -“ or some such. If Linde’s meter has a “beep” mode for continuity testing, that could be definitive.

I’m still saying it’s a short

You are trouble-shooting so you need to remove extraneous variables. So step one is:

Forget the circuit and the other components including the output jack. Remove the pickup from the circuit. Test the pickup on its own with nothing else connected. Still 0?

If it’s still zero, that’s what you need to focus on. Don’t worry any more about the circuit and changing the volume knobs or anything like that until the short in the pickup is resolved and you get an expected resistance reading, and not a 0.

Once the pickup is functional again, you can reintroduce it into the circuit.

Ok, guys, thank you.
Anyway, the two wires of the pickup are no connected at all. Sorry, my multimeter shows a "0", but that means there's no connection.
The 111k resistance when I ground the (working) bridge pickup is because the two 250k pots in parallel. Yes, the 111k resistance is a bit low (I expected 120k), probably the two pots are smaller than normal.
The (not working) neck pick is completely away from the circuit, as I said it, no connection and no resistance between the two wires.
I tried to connect the pickup directly in the amp through a bare jack, and it doesn't sound.

I'd say the pickup is broken, but I can't see the coil wire interrupted near the soldering in the eyelet. Maybe a bit of corrosion? Around the eyelet there's dirt and white.

There's a trick (not infallible) that someone else suggest me: to measure the capacitance between the a wire of the pickup and the magnets, the the other wire and the magnet. If I got 0pF from one side and some very very small value from the other wire, maybe the side with capacitance means that the coil is broken there.
Indeed, I got 0.000nF with the white wire and 0.002-0.009 with the black wire.

Probably, this bass needs a new pickup, but what do you think about that test?

Just being a technical stickler here:

An electrical short would mean the magnet wire insulation is stripped, and grounded to one or more of the polepieces. No usual issue there except when you touch a string to the polepiece, it will completely kill the signal, as it will send all output from the pickup to ground.

An open circuit is the correct term for a broken wire.

As for solving the issue, if the start and finish wires are connected to the eyelets securely (you can re-flow the solder joints to make sure), and the pickup isn't working, the easiest course of action is a rewind. Unwinding wrap by wrap searching for a broken wire is extremely time consuming and most likely a fruitless endeavor, and if rewinding the pickup is possible, a waste of time.

It's very common for the magnets to corrode on AlNiCo pickups. The reason being the copper in the magnet wire is prone to causing galvanic corrosion of the aluminum in the AlNiCo rod magnets. Most standard manufacturers will wind directly over the magnets with no barrier and this will inevitably lead to problems over time.

Pickups are extremely simple circuits. The only thing that can go wrong is a break in the coil somewhere, or the start or finish lead wire becoming disconnected. The magnetic Gauss strength is almost never the problem, with one exception:

On ceramic mag pups, where the mags are stuck onto steel poles with hot melt glue, occasionally the magnets will just fall off, and that will cause the pickup to stop working as now you just have a dummy coil without any electromagnetic induction.

...and a break in the coil that *isn't* the start or finish lead is almost always a problem deep in the coil -- corrosion.

My guess, especially since there's white around the eyelet, is you're dealing with corrosion, which eats into and destroys a large portion of the magnet wire wrapped around the polepieces, killing the pickup completely. I've rewound many pickups with this issue. I just wrap the magnets with thick black cloth electrical tape before rewinding the pickup.

Rewinding is pretty much always the quickest and easiest fix, barring cases such as a disconnected start or finish wire that can be reattached or spliced.

No harm in unwinding the pickup wrap by wrap though, if you have no way of rewinding it and it's dead anyway. Extremely unlikely you'll find the break, but you might. Then it's just a matter of getting enough of a length of the in-tact wire to wrap around the eyelet, re-solder, and done. But if the break is down around the magnets you're gonna be taking wraps off that coil for a very long time.

Thank you.
I talked with my friend, it's ok for him to buy a new set of pickups and give a new life to this bass. This Jazz Bass is an highway one, the pickups was nice, but a bit cheaper. The only pickup I could hear, the bridge one, I felt it a bit weak.

When I'll have back this bass I'm going to take a look at this pickup, again, just to see if I can see what's wrong with it. Whatever it is, new pickups will come for this bass.

Sure thing! I forgot to mention, try setting your meter to Mega Ohms. If you're on 20k, you're not going to get any resistance reading if there's a broken wire. At the "M" setting though, you might see something.

For reference, I made a YouTube video a while back detailing some finer points of damaged pickups as well here:

https://youtu.be/XDCHles5of4

I recorded a simple SD pickup repair I did as well. Unfortunately I wasn't able to get a really clear shot of me actually splicing the wire, but I did show the before and after.

https://youtu.be/1V6MWrivDio