Diagnosing My P

[velorush]

Finally got to plug in the new (to me) Cruisebass last night and discovered what I initially posted as needing a pickup adjustment was in fact a problematic P-Bass pickup.

The P pickup has far less output compared to the jazz pickup (I would think if anything the opposite would be the case).

If I tap on the P pickup cover it is quite loud compared to tapping on the jazz cover - tapping on the P polepieces with a screwdriver, however, yields softer 'clicks' than the of the jazz.

I didn't have time to really get into full diagnosis mode, but could it be shorted across the coils? Wouldn't be something simple like the volume pot, would it (actually, the control seems to work fine, taper-wise)?

[hamerhead]

Sounds like a professional chemical analysis is in order.

[carfish7]

Silly question, but looking at the knobs - everything full up? Try gently pushing down on or pulling up on the "P" volume knob and rotate- see if the wipers aren't happy.

I'd check wiring next. Getting "clicks" is a good sign for the pickup itself, assuming it is relatively even across all poles. Clean out those pots real well and inspect for loose or cold solder joints. See if you can tell if anyone has been in there messing before. Output good with the "J" pickup soloed? If so, you can likely eliminate the jack as the culprit.

[velorush]

Silly question, but looking at the knobs - everything full up? Try gently pushing down on or pulling up on the "P" volume knob and rotate- see if the wipers aren't happy.

I'd check wiring next. Getting "clicks" is a good sign for the pickup itself, assuming it is relatively even across all poles. Clean out those pots real well and inspect for loose or cold solder joints. See if you can tell if anyone has been in there messing before. Output good with the "J" pickup soloed? If so, you can likely eliminate the jack as the culprit.

Not silly at all. Yep, I tried full up, tried a bit less than full up (thinking maybe there was a bad spot on the resistance track, but it behaved correctly, just lower output than expected throughout the range. I pushed and pulled on the knob thinking it might be a wiper contact issue, nothing changed.

J soloed is fine - good output and really sounds great.

Interestingly, when both pickups were on, the volume reduced slightly (compared to the J soloed) as I would expect with two pickups in parallel. Lowering the volume knob of the P resulted in an increase in output due to the stronger J pickup.

I'm going to have to get the soldering iron out to really tell what's what. I'd like to check the DC resistance of the P pickup to see if it is in range and then check the pot out. I hate to melt those virgin solders, but it's of no use in the shape it's in. Maybe this weekend if I can fit it in between kids' ball games.

ETA: if it ends up being the pickup, are these DiMarzios relatively easy to acquire, or will I be forced to settle for a non-original replacement pickup? Hmmmm... gives me an idea. Oh donplob!

[murkat]

you have a ground fault somewhere on the P pup side.

Be it the volume or pup wiring.

check all solder joints, re solder them.

check for frayed wires.

check ground on volume pot, re solder everything associated with the P pups.

Those P pups should be loud as fuck, big J Lo bottom big.

[velorush]

you have a ground fault somewhere on the P pup side.

Be it the volume or pup wiring.

check all solder joints, re solder them.

check for frayed wires.

check ground on volume pot, re solder everything associated with the P pups.

Those P pups should be loud as fuck, big J Lo bottom big.

Will do. On my Fender, the P is much louder than the bridge humbucker - huge, thick, chewy bottom. So much so that I've been trying to get information on the Rio Powerbucker as it looks like a direct replacement for the bridge pickup.

I'll go looking for a ground fault. Should be easy enough to trace down with a multimeter.

[murkat]

meter will not show it as much as you want it too.

un solder the pups, get the ohm reading of them,

get the reading on the vol pot, the wiper read outs.

then resolder and get readings, and compare.

[velorush]

Assuming the pickup has a ground fault, is there a remedy other than a rewind? Unless one of the lead-out wires from the coil is touching the base plate, I can't imagine a scenario where a fix is other than a rewind.

[Jimbilly]

You've sprayed out the pots with De-Oxit? that would be the first thing I'd do. Both volume pots are the correct value? I suppose it's possible, however unlikely, that a non-correct pot could have been put in there. Agreed about the volume, that P pickup should be really loud all by itself, and you should not have a volume drop. Could you reverse the wiring for a test?: P to J volume knob, and J to P volume knob?, that might also help with the diagnosis without a lot of soldering, telling you if it's the pot or the pup.

[Armitage]

Judging by the corrosion on the pickguard screws, a spray of De-Oxit is the first thing I'd do too.

[murkat]

Assuming the pickup has a ground fault, is there a remedy other than a rewind? Unless one of the lead-out wires from the coil is touching the base plate, I can't imagine a scenario where a fix is other than a rewind.

you will be ablle to tell once you have it disconnected and metered if it is dead or not.

toucking up the solder spots won't hurt either.

[velorush]

Bought a fresh can of CRC contact cleaner ($20 at Fastenal!) and cleaned the pots. That definitely helped with a touch of crackly noise I heard in the J volume pot, but the P pickup output was about the same.

I noticed tonight, the A string is nearly as loud using the Precision pickup as with the Jazz pickup. The E is next louder followed by the D - given strings of the same size, I'm guessing these would be about the same volume - followed by the barely audible G.

DC resistance at the output jack was: P = 11.11kΩ, J = 6.42kΩ.

I pulled the P out to see if I could discern anything there:

Nothing seemed odd. I'll keep working, including re-flowing the solder, but that'll have to wait for another night.

Thanks to everyone for their interest and ideas!

[veatch]

I think I smell asparagus...

Sounds like the bottom half of the pup is dead - shorted most likely?

[AdmiralB]

Sounds like the bottom half of the pup is dead - shorted most likely?

Not likely. If it was a short, he'd see a lot less than 11K; if open, he'd see nothing at all.

Almost sounds like a magnet issue, but it's exceedingly rare for ceramics to get accidentally demagnetized.

[velorush]

I forgot to add (by the time I posted it was late last night!) that grounding seemed to check out fine using the ohm meter, but that doesn't necessarily mean anything I suppose.

Speaking of the magnets - they were loose. Well, one fell out when I lifted the pickup. I used the other pickup to ensure I had the proper orientation when I reinserted it into the rubbery silicone holder. It could very well be that the magnets are all out of kilter (improperly oriented) from someone pulling the pickups before.

Or maybe not...

This is really bizarre with the A string being so much louder than the others - the difference isn't an adjustment / proximity issue, I mean it is much louder.

[AdmiralB]

Ah, that's probably it. The magnets have to be installed opposing each other - like poles together. That's why you need adhesive, because they'll repel each other.

And they need to be oriented the same way as on the other coil, or you'll get a little bit of polarity cancellation (if the coils both spanned all strings, you'd get a LOT of cancellation).

If you have the magnets set up with dissimilar poles together, they'll stick, but your output will go down the drain.

[murkat]

^ they look stock, the glue to the magnets?

send them back to DiMarzio, under warranty

[AdmiralB]

Yeah, that's how the original Model P and Model Js were made - hot glue or the like, sticking opposing ceramic bars to the bottom a la P90.

[velorush]

Methodology: I pulled the coil covering E and A out first and a magnet dropped into the route. I pulled a magnet from the other coil and noted it repelled when moved on top of the magnet across the coil. I oriented the dropped magnet where it did the same and pushed it into the goo. Perhaps I should have studied the situation more closely...

Come to think of it, if it is a magnet problem, orienting the E/A coil magnets the same as the other, lesser-functioning coil only replicated the problem in the E/A coil. Of course, this is moot as neither coil was functioning properly before I opened it up (moot unless someone's been in here messing around before!). I suspect revisiting the magnets will likely be required.

ETA: how would I know I had the magnets properly oriented? I mean, there's getting all four oriented properly in the P pickup, but also I suspect it would need to be the proper polarity for good sounds when in parallel with the J pickup.

[murkat]

http://www.stewmac.com/shop/Tools/Special_tools_for_Electronics,_pickups/Magnet_Polarity_Tester.html?actn=100101&xst=3&xsr=11079

[AdmiralB]

Take all the magnets out.

Take one magnet and touch (or try to touch) its long edge to the top of the J pickup. If it attracts, that's NOT the edge you want - find the edge (long edge, remember) that repels the J poles, and mark it with something (Sharpie).

Take the other magnets and test their long edges against the Sharpied magnet edge. Mark all the edges that repel.

Assemble the coils with the Sharpied edges touching the polepieces.

[velorush]

Very logical!

But I have a question: since the P pickup is a humbucker, wouldn't I want one of the coils with opposite orientation so that the coils are reverse polarity?

That would entail having magnets on one with Shariped edges touching the polepieces and one with Sharpied edges facing away from the polepieces. Is that right?

[AdmiralB]

Ah, yeah. Forgot about that. Sorry!

[AdmiralB]

Now that I think about it, it might not matter regarding the separate coils...I wish I had a P-bass around here to check.

The humbucking effect is developed through wiring the two coils in opposing polarity...that cancels any noise induced identically in both coils.

That also has the effect of the "out of phase" tone, and swapping the magnet polarity brings that back around without affecting the noise-cancelling feature.

But since the two coils here aren't sensing the same string information, I'd be willing to bet there's little or no tonal distinction between having the two magnetically of like polarity versus opposing polarity.

[Jimbilly]

I just measured the Hamer/PJ Dimarzio set I have, it's 80s but the pole pieces are not visible, the backs look similar to what you have. The P is 11.52 ohms, the J is 6.5 ohms, -if that helps at all.

[velorush]

Now that I think about it, it might not matter regarding the separate coils...I wish I had a P-bass around here to check.

I know absolutely nothing about P-bass pickups. My assumption was based on construction of a guitar humbucker, where the coils are reverse wound/reverse polarity from each other. If the P construction is the same, the polarity, as well as the direction of the coil wire, would be reversed. I'll do some Googling.

I just measured the Hamer/PJ DiMarzio set I have, it's 80s but the pole pieces are not visible, the backs look similar to what you have. The P is 11.52 ohms, the J is 6.5 ohms, -if that helps at all.

Looks like the J is right on with yours and, if anything, the P is a bit weak - though probably within spec. That's great help as I knew nothing about what was correct. Thanks for posting.