Pickup dying

[okabass]

As we know many old 7ender PUs tend to die. Has somebody good explanation why this happens?
What I have found sometimes the magnet gets rusty (?), and that swells and breaks the thin insulation or the wire. And makes a short to magnets. Or the insulation deteriorates for some reason: age, moisture, sweat, vibration... Or the wire was winded so high tension that it is just at the edge of snapping. And then snaps after sometime, years, decades?

[Helmholtz]

What I have found sometimes the magnet gets rusty (?), and that swells and breaks the thin insulation or the wire. And makes a short to magnets.

A short to one of the magnets/poles can be detected with an Ohmmeter.

Or the insulation deteriorates for some reason: age, moisture, sweat, vibration...

This all makes sense. Would most probably cause shorted turns and would make PU sound dull depending on number of turns involved.

Or the wire was winded so high tension that it is just at the edge of snapping. And then snaps after sometime, years, decades?

That should make the PU read open ("OL").


You forgot to mention one common reason: Someone tried to push in a magnet. Especially risky with lacquer potted PUs, where the wire tends to stick to the magnets.

[okabass]

Thanks answering, Helmholtz.
I mean the chain of events why a working vintage 7ender PU dies by itself. Not by a screwdriver or pushing the magnets.

[J M Fahey]

Then most probable culprit is plain old corrosion.

red shiny copper loves to turn into green/brownish mud ... it only takes time.

[Mick Bailey]

I've sometimes found that an otherwise good pickup can have just a spot of green corrosion on the outer layer. Just enough to make a pickup read much higher DC resistance than expected. The pickup will often work but have low output and sound generally poor.

Guitars are basically a wooden sponge. Some Teles steam when you bore the bodies for an electro-socket and the shavings come off damp.

I find cased guitars suffer more from internal corrosion than those left out on stands. Many cases quickly absorb moisture but are slow to dry out. A bit like keeping a guitar between the pages of a wet book.

[eschertron]

A bit like keeping a guitar between the pages of a wet book.

I'm not sure that deserves a 'like', it's more of a "hair standing up on the back of my neck" reaction. But, thanks for making that observation!

[Lollar Jason]

i always reheat the solder joints on old fenders that are dead and one out o-f 10 or 20 work again so that would be either the insulation wasnt stripped off perfectly in combination with corrosion traveling down the wire into the solder joint- not really sure but I know its worth re-soldering.

[okabass]

HI
Thank you all answering.
Resoldering is worth of trying all (decades) old solder joints. Also in amps and effects.
My basses ('65 P and '68 Tele) have problems with PU's coilwire touching the magnets. As far as I hear it doesn't alter the PU's sound. When you measure the resistance between the start and a magnet you get not ∞ ohms but some ohms or kilo-ohms resistance. I managed to get it better by putting electric spray in the PU. I doesn't fix it complitely, but may slow the dying process and the
need to rewind.

[Helmholtz]

If just one wire turn contacts a magnet, PU sound won't change. It requires more than one turn contacting the same magnet to produce some detrimental effect.

Corrosion typically requires some moisture / water molecules + a little contamination with salts or acids (as contained in sweat or coke). One of the best ways to keep moisture out of PUs is thorough (best case: vacuum) wax (paraffin) potting, as wax is hydrophobic (water repellent). Leo Fender knew: Fender - Wax Potting pat4885970.pdf

So if one of my vintage strat PUs would develop the described symptoms, I would not use any contact spray (which is intended to improve contact), but rather re-pot the PU preferably in wintertime when environmental humidity has been low for some time. The main purpose would be to fill any voids between magnets and wire with paraffin. Also drying the PU in an baking oven at 60 to 70°C for some hours before potting makes sense.

This said, some contact cleaners may actually be water repellent. But I tend to not consider them a permanent cure as long as water can creep in along the poles.

[okabass]

HI

I just measured ( Fluke 179) my '65 P pickup. To my delight it shows ∞ ohms between the start and the magnets . Before it shows 140 kΩ between the start and a magnet. My "treatment" seems to help, at least this PU. The coil wire is Formvar, I think (copper color), which properties are not very good (So I've read).

[Helmholtz]

HI

I just measured ( Fluke 179) my '65 P pickup. To my delight it shows ∞ ohms between the start and the magnets . Before it shows 140 kΩ between the start and a magnet. My "treatment" seems to help, at least this PU. The coil wire is Formvar, I think (copper color), which properties are not very good (So I've read).

So you were lucky and I hope you can preserve this condition. (BTW, are you sure the previous value of 140k was real and you did not touch the probe tips with your fingers while measuring?)

Anyway, your positive result will not change my general assessment regarding the use of contact cleaners in PUs. Also I fear that the residue of contact cleaners might prevent good future re-potting results.

Apart from that I really like Deoxit for cleaning and improving contacts.

Didn't we have a similar discussion a while ago?

[okabass]

Hi
I'm quite positive I made correct measuring.
I used a Finnish product, PRF 7-78.
Yes I think we did. I wrote my spray experiments.
I'm not saying that spray+heat etc. cures all PUs, but it worked here. And worth of trying if there seems to be no other option than rewinding the PU.
https://www.ikh.fi/fi/puhdistusaine-...8-220ml-prf020

[David Schwab]

Fender didn't tape off the magnets before winding. After a while moisture gets in between the magnets and coil wire, and it can corrode the wire, partially because of the interaction between the aluminum in the magnets and the copper wire.

Leo patented wax potting as a way to stop moisture from getting in the coil. The easiest way is to tape off the magnets with masking or Kapton tape before winding.

[Mick Bailey]

Older Seymour Duncan pickups are also wound directly on the magnets.

[Helmholtz]

The Fender (1965) assembly instructions prescribed lacquer dipping of the magnets-flatwork assembly before winding and potting, probably in order to stabilize the assembly and insulate the magnets. But I think they not always allowed for enough drying/curing time.