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Wiring Help - Tone Pot

Discussion in 'Pickups & Electronics [BG]' started by whoatherechunk, Dec 26, 2013.


  1. whoatherechunk

    whoatherechunk Supporting Member

    Joined:
    Apr 4, 2008
    First off, I know this is a guitar related post but I thought you guys could help!

    Hey guys,

    A friend of mine owns a MIJ JD Tele. He said that his tele wasnt working and that perhaps some wiring came loose since the volume knob and tone knob felt loose. My first thought was that some wiring came off. When I took off the control plate I saw that the white wire to the middle lug of the volume knob was disconnected. I immediately soldered that and voila finally the guitar was audible. However, I saw that the .05 (?) cap lead had come off from somewhere. It's soldered to the middle lug of the tone knob and intuitively I thought that the other end should either be soldered to the back of the tone pot or jumped to the middle lug of the volume pot. Needless to say, I tried various ways of wiring and the main thing that occurred was that the tone knob acted as a volume knob. I'm guessing that this could be either faulty wiring, a blown cap, or a short in the pickup (?). Interestingly, there was never anything soldered to the back of the tone pot. I attempted to solder the ground from the jack and solder the other end to the capacitor as the "schematic" shows but interestingly nothing was ever soldered there before. Eh, I'm stumped. Can someone please help? Thanks!

    My friend's guitar:

    [​IMG]


    Sample of wiring on another JD Tele

    [​IMG]


    Schematic I found online

    [​IMG]
     
  2. michaelandrew

    michaelandrew The bass player is always right. Supporting Member

    Joined:
    Dec 27, 2010
    Location:
    Ottawa, Ontario, Canada
    That's the same tone circuit as used on J basses and many others. The 0.05 uF tone cap goes from the tone pot center terminal to ground - that is, solder the other end to the back of the tone pot.

    A "blown" cap is unlikely in a passive circuit but that one looks like it might be damaged some other way (hard to tell from the pic). It won't hurt to try it though - just don't overheat the pot when soldering. If that doesn't work, try replacing the tone cap.

    Hope this helps.
     
  3. Chainsaw Willie

    Chainsaw Willie

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    Nov 6, 2011
    Location:
    Redmond, Washington
    There was originally no solder blob on the back of the tone pot?

    Perhaps the tone cap originally went between the center lug of the tone pot to the grounded lug of the volume pot. It doesn't have to go to the pot body, it is just often done because that is a conviienient ground point. It can be tied to any part of the circuit that is grounded ( or "return" ).
     
  4. Chainsaw Willie

    Chainsaw Willie

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    Redmond, Washington
    Oh yeah, looking at the first pic. I don't see a ground/return wire going to the tone pot can. Unless the black paint in the cavity is REALLY conductive, soldering the tone cap to the ungrounded pot can will do nothing. It will not work as a tone control unless that cap has one side to ground. Soldering it to something ungrounded is like not installing it at all.
     
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  6. Chainsaw Willie

    Chainsaw Willie

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    Redmond, Washington
    Also, the Jerry Donahue wiring diagram does not show a complete ground circuit. It will not work as shown. All grounds/returns must be tied somehow to the output jack. In this diagram only the tone pot is tied to the jack. The pickup return is not, nor is the volume pot. This diagram is missing a wire from the volume pot can to the tone pot can.

    This wiring would only work in a metal shielded control cavity.

    It really doesn't matter if you run a single wire from everything, daisy chain stuff, or if you use the cans as a ground buss, or how exactly you wire the returns, but they all must somehow connect together and to the outer ring of the output jack.

    This is a good example of why wiring diagrams are inferior to schematics. You cannot immediately see a failure in a wiring drawing, but in a schematic it is obvious.
     
  7. Chainsaw Willie

    Chainsaw Willie

    Joined:
    Nov 6, 2011
    Location:
    Redmond, Washington
    Doh!
    It's a Tele!
    All that stuff is mounted on a metal plate! That's the undocumented ground path.
    I am so sadly full of crap.
     
  8. whoatherechunk

    whoatherechunk Supporting Member

    Joined:
    Apr 4, 2008
    Yea, originally there was NOTHING soldered to the back of the tone pot. It may only seem like it because I tried soldering the cap to the back of the tone pot and it still acted like a volume knob. :meh:

    Yea, I tried that and it still acted as volume pot.

     
  9. whoatherechunk

    whoatherechunk Supporting Member

    Joined:
    Apr 4, 2008
    That's why I'm guessing it's the capacitor. I'll just try and see if they have one at Radio Shack.
     
  10. Chainsaw Willie

    Chainsaw Willie

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    Redmond, Washington
    Does the guitar play, and the volume control work if you remove the tone cap entirely?

    It the cap was shorted it would dump all frequencies to ground and work like a crappy attenuator. Check the actual value of the cap too. A large value will dump all frequencies to ground .

    Temporarily remove the tone cap. Plug in the guitar to an amp and see if the volume control and pickup selector work. It might be really bright, but everything but tone control should work. If it does, then that cap is bad, shorted, or somebody installed the wrong cap.

    How old is the guitar? Ceramic caps are pretty old-school, and I see green poly chicklets in the other photo. Are the ceramics stock?
     
  11. whoatherechunk

    whoatherechunk Supporting Member

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    Chainsaw, when I removed the cap the guitar worked normally except it sounded thin and tinny - which is what I expected.
     
  12. Chainsaw Willie

    Chainsaw Willie

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    Yeah, you got it then, suspecting the cap.

    Bad caps in passive guitar circuits are rare, but it looks like that's what ya got. It makes sense that if the pots were loose that they worked back and forth and damaged the cap leads, twisted the leads, or the part where the leads attach inside the cap are mucked up.
     
  13. whoatherechunk

    whoatherechunk Supporting Member

    Joined:
    Apr 4, 2008
    Hopefully the cap is the culprit. So before I actually replace the cap either I can solder it to: 1.) back of the tone pot (most logical place but it wasn't there originally) 2.) back of volume pot or 3.) middle lug of the volume pot ?

    Not sure might be my best option or what was done stock.

    Thanks!

     
  14. Chainsaw Willie

    Chainsaw Willie

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    No on #3, not the middle lug of the volume pot, that won't work. The outside lug that is already tied to the volume pot can is a good spot.

    On the photos of the red Tele you provided, it looks like the tone cap is attached to the middle lug of the tone pot, and the grounded end goes thru the outer lug of the volume pot and continues thru to the volume can. It looks like the cap lead grounds both the cap and the outer volume lug.

    I would tie to the volume pot can or that outer volume lug because there is the black ground wire tied there. It is a more reliable ground.

    The tone pot can is grounded through the chromed metal mounting plate. I wouldn't rely on this path. Or I would run a wire from the volume can to the tone can if I really wanted that cap soldered to the tone can.

    Really there are a zillion ways to make it work, as long as all these grounds somehow tie to the output jack outer ring.
     
  15. Lownote38

    Lownote38

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    Nashville, TN
    That bigger cap (the disconnected one) looks eaten up like it was burned by a soldering iron. That would certainly render it blown. I would replace the cap and wire as your schematic says to.
     
  16. whoatherechunk

    whoatherechunk Supporting Member

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    Apr 4, 2008
    It was definitely the cap. Thanks guys.
     

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