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P-rails + 2 push pull debugging

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  • P-rails + 2 push pull debugging

    Hi all! I recently did my first build and followed the wiring diagram here:
    Click image for larger version

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    I grounded the bridge and I got it all wired up and then plugged it in to play. Unfortunately, I had a few sad observations:
    • There is a lot of static noise for all the pickups (3 way switch). A LOT.
    • The bridge pickup seems to not be working at all.


    The neck pickup works fine and the push pulls seem to be working properly to select the p90 or the rail. I did a visual inspection and it appears as if the wires are all connected properly. Then I dug out my multimeter and began to probe around. I noticed that the bridge pickup doesn't seem to be seem by the circuit...instead it appears as the value of the pot (e.g. 500k at max) when measured between signal and GND.

    To be honest, I have no idea what steps to take next here. I was wondering if it was a bad CTS pot, but the push-pull selector feature seems to work so not sure..

    For the static, I think I just need to go through and make sure the solder joints are good before going deeper. All of the pot grounds (on the back) are connected to the plug GND, so I'm good there.

  • #2
    Re: P-rails + 2 push pull debugging

    Sounds like the bridge is just out of circuit. The problem is, there are more than 6 possible connection points that could be bad leading to the problem.

    If it were me, this is how I would figure out where the problem is.

    There's a jumper wire between the push-pull switches that connects the bridge red and white when the switch is down. Put a probe on the lug on each side of that jumper and see if you get continuity. If not, retouch both jumper/lug connection points with a solder iron.

    If the jumper connection is fine, I would move to the red and white bridge connections. Put the probes on the black and green wires of the bridge and see if you get a resistance reading. If so, the red and white connections are good. If not, you'll have to test all 4 connections. Put the test probes on the red/white lugs and see if you get continutiy through the switch and jumper, then put the probes on the red/white wires directly and see if you get contintuity through the switch and jumper. If you don't get continuity from the lugs, either the jumper or the switch might be bad. If you get continuity through the lugs but not the red/white wires directly, one of those red/white connections is bad. Retouch the bridge red and white wire/lug connections with a solder iron. Test the red white wires for continuity through the switch and jumper, then put the probes on the black and green wires of the bridge and see if you get a resistance reading. If so, the red and white connections are good, finally.

    If you still get no sound, then you need to check the jumper from the bridge side of the push-pull switch to the volume pot. Put the probes on the push-pull switch lug where the bridge black is attached and the outside bridge volume lug where the push-pull is jumpered to it. If you get continuity, it's good. If not, retouch the jumper connecting the bridge side of the push-pull to the bridge volume pot.

    If all of that doesn't solve it, then need to move to other areas of the circuit. But I believe it's one of the 4 bridge connections that is bad, because you are getting a reading of the volume pot.

    Comment


    • #3
      Re: P-rails + 2 push pull debugging

      Thanks for the reply! Let me list out my push-pull config real quick and then I can respond to your post:

      Bridge CTS push-pull:
      • 1 = connected to bridge black wire and jumpered to bridge volume connector (on diagram)
      • C1 = connected to bridge red wire
      • 2 = jumpered to neck push-pull 4
      • 3 = connected to neck black wire and jumpered to neck volume (as in diagram)
      • C2 = connected to neck red wire
      • 4 = connected to neck push-pull 2


      I noticed something different about my neck CTS push-pull wiring than the diagram, and I'm wondering how it would manifest in the circuit... the green wire on the rail is supposed to go to GND, so on the bridge the rail is floating. Not sure why the whole pickup wouldn't work though even for the p90?
      • 1 = connected to neck pickup green and jumpered to GND
      • C1 = connected to white neck pickup
      • 2 = jumpered to 4 on bridge push pull
      • 3 = connected to bridge green BUT NOT JUMPERED TO GND
      • C2 = connected to to bridge white
      • 4 = jumpered to 2 on bridge push pull


      With respect to the measurements:
      • Jumpers between the push-pull switches are connected
      • Putting ohmmeter between black and green of bridge shows 18.4k ohm
      • Looks like I get continuity on the other connections...
      • (bridge red & bridge white) between the wires (C1 to C1 on the push pulls), 500k
      • (neck red & neck white) between the wires (c2 to C2 on the push pulls), 500k
      • (bridge red & neck white) between the wires (C1 to C2), 0 ohm
      • (neck red & bridge white) between the wires (C2 to C1), 0 ohm
      Last edited by jonnyd42; 07-13-2020, 08:25 PM. Reason: more text

      Comment


      • #4
        Re: P-rails + 2 push pull debugging

        Originally posted by jonnyd42 View Post
        I noticed something different about my neck CTS push-pull wiring than the diagram, and I'm wondering how it would manifest in the circuit... the green wire on the rail is supposed to go to GND, so on the bridge the rail is floating. Not sure why the whole pickup wouldn't work though even for the p90?
        • 3 = connected to bridge green BUT NOT JUMPERED TO GND
        This is your problem. Bridge will never work if the negative/green wire isn't connected to ground.

        Comment


        • #5
          Re: P-rails + 2 push pull debugging

          Everything works great now! I also fixed the noise issue by isolating the problem to the jack - the signal was being voltage divided by my copper tape insulation (which is GND) and would rub against it. Shielded everything in that area with electrical tape and now it's silent!

          Thank you so much.

          Comment


          • #6
            Re: P-rails + 2 push pull debugging

            I'm glad you got it working. Just out of curiosity, did you consider using Triple Shots?

            Comment


            • #7
              Re: P-rails + 2 push pull debugging

              I did consider that. I also bought a pair . On installing them, the ribbon cable snapped on one.

              I wasn't happy with the build quality (plastic mount, cheap switches, poorly made ribbon cable) and I didn't want to have to gut my electronics in a few months when they both inevitably break....so I switched plans to this wiring.

              Comment

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