Same polarity pick-ups on a MIM Jazz?

[SweetMelisma]

I do instrument repairs for my old high school and they have two MIM Fender Jazz Basses. They hum like mad in the band room (with some really electromagnetically bad lights), even with both pick-ups full on. I checked them out with my trusty Lego magnet and sure enough, both basses have two pick-ups of the same polarity. And based on pick-up dimentions and polarity, I'd say they're both bridge pick-ups. So on these two basses, I have a total of 4 bridge pick-ups.

If you were to define the major characterists of a Jazz Bass, you would probably mention the hum-canceling effect of using the two pick-ups together, so I don't think I'm just missing something on how jazz basses work.

I know the answer is to of course buy new pick-ups, but I'm curious, has anybody ever heard of this before?

[T-Bird]

Hi.

Just probably Monday or Friday versions .

The pickups in a J are so far apart that the magnetic field orientation shouldn't make no difference what so ever, but it's obviously easier to reverse the field in mfg to be able to use the same coil in both pickups.

Just flip the field and You're back in business.

BTW, excuse my ignorance about J's, but shouldn't the PU casings be of different sizes for the neck and bridge PU?

Regards
Sam

[SweetMelisma]

Yes, they should be different sizes. The pick-up that is currently in the neck in these guys fits in the wood, but the pole-pieces don't line up properly on the strings. Poor alignment can cause extra transients. Getting rid of these transients is the whole reason Leo Fender used two pole-pieces, one on either side of the string.

As far as the polarity goes, I know pretty well how this stuff all works electro-magnetically, and I've even looked into how to "flip" them. However, my question is more about the history of this occurance. Is this a common mistake on MIM Jazzes?

[Bobster]

Older MiM Jazz basses have the same size pickups and routes. This was changed around 10 years ago (Fender experts feel free to chime in). It was cheaper for Fender to do it that way. Only one size pickup to mess with, one size route. For example, my '98 has the same size routes.

You should be able to flip the leads on one of the pickups by un/resoldering the leads at the pots and swapping them. If it's strictly a polarity issue, that should resolve. But some shielding is always a good idea.

Best of luck,

Bob

[AtomicPunk]

I noticed this on a 5 string Jazz I recently picked up. Both pickups soloed sound ok, although the bridge pickup has WAY less volume than the neck PU, but when they are both on, it has a little bit of a chorus-y sound to it. Would this be a polarity issue?