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weird P-bass pickup failure

Discussion in 'Pickups & Electronics [BG]' started by Garden Variety, Jun 3, 2014.


  1. All,

    I had my bass poop out at last practice. Fender MIM p-bass, 2004, all stock. In the middle of a song, sound simply stopped. Took a few mins to conclude that it was the bass and not the amp or cable; there was a spare at the practice space to confirm the problem source, and finish practice.

    Got home and plugged in to start diagnostics. Nominally no output (possibly a touch at full amp vol, but there was also a little hum, and I was reluctant to leave everything dimed and start messing, only to find it was a jack connection....). Pulled scratch guard for a visual, no obvious issues. Plugged in cable and DMM shows @4.7k DC resistance. For kicks, I reflowed all solder joints on jack and pots, no change at cable tip. So I pulled the pickups completely. DC resistance for each half was @2.36 and 2.35k. I guess I was expecting one to measure somewhere north of 5k, and the other way low. I honestly have never measured this instrument's pickups, but it's very close in playing volume to my back-up bass (Peavey Milestone II), which is a normal @10.5k, so I'd expect similar for the Fender.

    I have never had a pickup, bass or guitar, fail, so I'm flummoxed. No shock that a pickup could fail, but sure seems unlikely that both of the splits would huff it simultaneously. Would one shorting then cause the other to short identically?

    Other explanations?
     
  2. If you measured while the pickups were wired up, then the resistance of the rest of the circuit is parallel to the coils.

    Though a 10.5k pickup would need to see a 8.5k parallel resistance to create 4.7k.
     
  3. Pickup were completely removed from instrument. I measured the 4.7k total at instrument cable tip PREVIOUS to disassembly (so expecting @10.5-10.7k), with the pots wide open. Measured them removed from circuit, but connected still in series, same 4.7k total. Separated the two split halves, they measured 2.36 and 2.35k (can't remember which was the higher one).
     
  4. If you've tested the jack, then its probably just the volume pot. Try testing it with your multimeter.
     
  5. Volume pot? There is no volume pot. I have two pickups (2 halves of a split P bass pickup) COMPLETELY REMOVED from the instrument. I am looking for explanations as to why the DC resistance would measure approximately 4.7k in series when it should measure approximately 10.5k (or why the halves separated would measure @2.35k each). Is anyone reading the OP?
     
  6. megafiddle

    megafiddle

    May 25, 2011
    My MIM P bass, bought new last year, measures 4.89 kohm at the jack.
    So that low of a value sounds normal. I don't think the problem is in the pickup.

    And it would be very unlikely for both halves of the pickup to fail in the same way.
    A fault in one half, would not cause a fault in the other half.

    -
     
  7. I appreciate the interests in commenting, but again, please read the OP before posting.

    I am not measuring at the jack. 4.7k is right off the pickups removed from the instrument, but still connected in series (FWIW, I got the same measurement when I did check at the jack, before disassembly). If you got 4.89k at the jack of a good Fender P-pass, you are on the wrong DMM scale (should be on the 20k scale) or your vol pot wasn't open fully. Approx 10.5k is completely typical for a P-bass, is also what I measured at the jack on my backup Peavey, and is pretty typical for many aftermarket P-bass replacement pickups; 4.89k is not normal. I also have a leftover set of pups from a Yamaha RBX that are measuring around 7.8k, and I sure remember that bass having lower volume until I swapped in a set of used MIM pups.

    > And it would be very unlikely for both halves of the pickup to fail in the same way.
    >

    Agreed. That is why I am confused. I could bother wiring in a different set of known-good pups to the bass, but what is the point when I already have an obvious red flag issue. I can't find anything wrong with this pup set, other than less-than-half output. It's like the magnets degaussed or something.
     
  8. I read your post mate. Please calm down I'm trying to help you.

    My "other explanation" as to why your
    is that there's nothing wrong with the pickup, and you should test the pot or jack! It may also be a short in the wiring.

    Also in your first post, you said that there was
    , but now you say there's
    So have you put it back in, and now it's at half volume?
     
  9. megafiddle

    megafiddle

    May 25, 2011
    The volume pot is the the only other DC path in the circuit, and I did have it on max vol.
    My vol pot is 250 K. The total parallel resistance is 4.89k, measured at the jack. That works out to about 4.998k for the pickup alone.
    The pickup is as new, and works fine. I don't have to pull it out and measure it. I can assure you that this pickup itself is about 5kohm.

    -
     
  10. M.R. Ogle

    M.R. Ogle Gold Supporting Member Commercial User

    Nov 5, 2004
    Mount Vernon, Illinois
    Backstage Guitar Lab owner
    I found this thread after a search...because I have a pair of P-bass pickups of unknown provenance that are also reading low. 2.3K ohms for each coil separately and 4.65 approx for both. Odd thing, they seem to be working just fine. But with my other P-pickups usually around 10.5K ohms, I was wondering if this was unusual, or the new normal?
     
  11. Growlmonkee

    Growlmonkee

    Jan 30, 2013
    Florida, U.S.
    Just a thought, a jack could look good, and be shorted in the insulating plates,( might even seem fine without a plug in it), you may have already, but, if not try a different jack.
     
  12. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    plated steel poles, with ceramic bar magnets on the bottom?

    that's normal for fender mexi standard pickups; less wire (hence the low readings) but the steel pole/bottom magnet construction is actually more "efficient", so they're still plenty loud.
     
    petrus61 and M.R. Ogle like this.
  13. M.R. Ogle

    M.R. Ogle Gold Supporting Member Commercial User

    Nov 5, 2004
    Mount Vernon, Illinois
    Backstage Guitar Lab owner
    YES!

    Wow. I learn something new every day. Thank you (again) Walter for sharing your knowledge.
     

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