Sound stopped on vintage Precision Bass - wiring resistance values, tips, advice?

Discussion in 'Pickups & Electronics [BG]' started by kiat, Aug 3, 2016.

  1. kiat

    kiat

    Aug 31, 2010
    Mons, Belgium
    Hi,

    Help sorely needed with likely resistance values for orignal pots, wiring and pickups. I'm new to getting into guitar/bass internals, this is the first time I've even taken any pickguard off.

    The other night my bass ('73 Precision Bass) stopped making much of a sound whilst I was practising and what I have done so far hasn't fixed it. The volume pot works, but the tone pot now just gives me a tinny sound if anything. I carefully took the electronics out and back a few times to test if there was any improvement - alas not.

    I spent some hours reading forums, fender wiring diagrams, etc and bought a multimeter today, to try and figure out what is broken. I'm getting some values, for example, A-P = 5k but B-C = 223k. But without knowing what the values of readings between or within components makes it very difficult to know what part or wire is faulty. I'm loathe to desolder anything without being sure about which part is faulty.

    Any info, tips, advice would be much appreciated.

    [​IMG]
     
  2. megafiddle

    megafiddle

    May 25, 2011
    The problem is easy - 223K between B and C is way too high. It should be similar to the resistance between A and P, which sounds correct. Those values are the resistance of each pickup coil.

    The fix may also be easy if it just a solder connection at the pickup terminal that failed.

    I would first try resoldering the connections at the pickup terminals B and C. Heat them just long enough to add a little bit of fresh solder. That may re-establish the connection. The resistance on that coil will then read about 5K.

    If not, you may have a coil wire that corroded through at the terminal. Depending on which end of the wire has lost contact, this could also be fixable. One end of the coil wire runs into the center of the coil. if this wire is broken at the terminal it will be very difficult to make connection to it again. The other end of the coil wire runs to the outside of the coil. If this end is broken, some extra length can be unwound from the coil to make a new connection at the terminal.

    In the event that simply resoldering the terminals doesn't help, then you will need to heat the terminals and remove the red and white lead wires. Then the solder should be removed with a solder vacuum or wick. A good inspection with a magnifier should reveal if a wire is broken at the terminal. You should see several turns of coil wire wrapped through the terminal eyelet and the portion of the wire inside the eyelet should be tinned. If you remove the coil bobbin from the cover, you will see the coil wires running to the terminals. Look for any break on the inside of the bobbin, where the wire runs from the coil to the terminal eyelet.

    The coil magnet wire is extremely delicate. Try not to disturb it any more than necessary in determining if it is broken at the terminal. If it is the outer coil wire that is broken, remove the old wraps from the eyelet, unwrap a turn of wire from the coil, and wrap a few turns through the eyelet. Then solder the new coil wire end to the eyelet, adding just enough solder to fill the eyelet. The enamel on the wire should burn off and allow the conductor to become tinned. Check with the ohmmeter, if you read about 5K, it is fixed. Reheat each terminal connection and stick the tinned end of the pickup leads back into the eyelets.

    If both ends of the coil wire are connected to the terminals, and it still reads high resistance, then the wire is broken internal to the coil. The only fix then is replacement or rewinding.

    -
     
  3. kiat

    kiat

    Aug 31, 2010
    Mons, Belgium
    Thanks megafiddle. There's a maker space at work that has those tools, I'll investigate using your walkthrough. Also, in case of pickup rewinding or messing up, I've reached out to some luthiers in the county I found online.

    If by any slim chance there's anyone from Belgium reading this - any recommend luthiers around Mons?
     
  4. kiat

    kiat

    Aug 31, 2010
    Mons, Belgium
    This is where I'm at after following excellent tips of resolder and also the unwind an external loop and resolder - still at 230K Ohms. Will ask specific rewind advice in a separate thread.
     
  5. megafiddle

    megafiddle

    May 25, 2011
    Sorry to hear that it wasn't an easy fix.

    Hopefully you can get it done for a reasonable price.

    -
     
  6. Growlmonkee

    Growlmonkee

    Jan 30, 2013
    Florida, U.S.
    It's a fair guess that one half of the pickup you are getting a good reading of 5k, from A to P, to get 230k from B to C, you are most likely reading the resistance of the volume pot, (it should be in that range), and there is no connection through the pickup's coil, if you have carefully tried Megafiddle's good advice, and getting the same results, it's a fair assumption that there is a break somewhere in the windings, on the B/C pickup half. Your options, if that's the case, are to have the pickup rewound, or buy a new pickup. If it were my bass I would consider saving all the electronics as they are, because they are original, and valuable, and replace everything... pickup, pots, jack, all new, probably with a vintage sounding new pickup, (the price would still be less than rewinding the pickup you have), or.... send both halves of the pickup to a good pickup specialist, and ask that they be made as new again, carefully clean up those pots, and jack, and put it back together. The taper, or resistance curve on the pots is called "audio taper", (it may vary just a little), the resistance value on the pots is 250k ohms, and the volume and tone pots are the same, the tone capacitor is (most common) .047μf, and any capacitor with that value will sound about equal, just a few options from someone who's been where you are