Shorted turn detector

[tbryanh]

... a shorted turn or two won't have enough of an effect on the Q factor to give an unambiguous indication, no matter what method you use to measure it.

Yeah, if the shorted turn is as insignificant as it appears to be, then determining if it exists would be like trying to find a needle in a hay stack.

[tbryanh]

What about a Strat with an aluminium pickguard: isn't that just another shorted turn (and a pretty big and beefy one at that)

Maybe not. The metal housings of transformers probably do not act as shorted turns. This is probably because the iron core keeps the magnetic field concentrated in the coil.

The same probably hold true for pickups. The magnets act as cores that keeps the magnetic field concentrated in the coil.

If the coils had air cores, then the housings might act as shorted turns.

[tbryanh]

OK, well I tried more or less what R.G. suggested. I took a cheap potted humbucker that I removed from my old guitar, connected a neon bulb across it, (leaving out the 100k resistor because I reckoned the pickup DCR would be enough) and tried prodding it with a 9V battery.

Nothing happened.

You might reverse the connections to the pickup and try again, or replace the alnico slugs with steel slugs.

Your test may have been sending the current through the pickup in a direction that created a magnetic field in the coils with the same polarity as the magnetic field from the alnico slugs. It may be that the net magnatism does not increase much, so that when you stopped the current flow, there was only a small collapsing magnetic field.

Sending the current through the pickup so that it creates a magnetic field with the opposite polarity as the magnetic field from the alnico slugs might work better. Here the net magnetism would be less than the magnatism from the alnico slugs, and there would be an expanding magnetic field when the current is stopped, hopefully a large expanding magnetic field.

Ultimately it might be best to replace the alnico slugs with steel slugs. This probably would make the pickup resemble a transformer much better.

[Zhangliqun]

Maybe I'm missing something here but...isn't just easier to check for a shorted coil with the ol' multi-meter?

[tbryanh]

Maybe I'm missing something here but...isn't just easier to check for a shorted coil with the ol' multi-meter?

If the whole coil was shorted, then an ohm meter would work, the coil would read 1 or 2 ohms instead of about 10,000 ohms.

Here the whole coil is not shorted. There is only a turn or two shorted somewhere in the coil. This might reduce the resistance reading of the coil by 1 or 2 ohms.

When you are reading 10,000 ohms, it is hard to tell if the reading is a couple of ohms off. Plus you need to know precisely what the coil should read before making the measurement, and this information is usually not availlable or is not possible to determine. Also, the temperature of the coil can affect the reading by a few ohms too.

So it appears testing with an ohm meter is not possible.