Help with pedal pcb

Discussion in 'DIY Effects Forum' started by StratPlus97, May 10, 2020.

  1. StratPlus97

    StratPlus97 Senior Stratmaster

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    I had a 10k pot crap out on me and tried to replace it. Of course I probably kept them iron on for too long and I broke off the small little copper(?) ring that one of the pot legs goes into. Not sure what that little thing is called. How and can I fix or replace that?

    [​IMG]


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  2. rgbedard

    rgbedard non-compliant Strat-Talk Supporter

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    It's called a land.

    You can remove the solder mask (the blue color) to expose the trace (printed circuit wire), and solder directly to that, using a bit of wire if necessary. No big deal, but require a little finesse so as not to make it worse. Too much heat will lift the traces off the board ... as you already discovered.

    Edit: now I can't tell if that is "just" a mechanical connection for the pot or electrical. I was of course speaking in an electrical context. Does it go through? Is there still a land on the other side of the board?
     
  3. VMamp

    VMamp Strat-Talk Member

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    Difficult to give good advice regards these sort of problems but, from what I can see, the area of the track that has been damaged possibly connects to the other side of what I think may be a Double sided pcb. I can see the damaged track plus another joint to the right and what appears to be three more solder joints in the lower part of the circle you have drawn.

    Before I start giving possible solutions I would like to see a picture of the potentiometer as I need to know if the potentiometer you removed has a support casing that was soldered to the pcb?
     
  4. StratPlus97

    StratPlus97 Senior Stratmaster

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    Thank you, I appreciate the help. Sorry for my ignorance. I just bought a call “How to Modify Guitar Pedals” book because I want to learn all of this stuff but I should have waited until I actually read it to tinker with things... I just can’t help myself though.

    Anyway, here are the photos. I believe this is a double sided PCB.
    *the problem is the “treble” in the middle where the 10k pot goes.

    [​IMG]
    [​IMG]
    [​IMG]


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  5. Guitarmageddon

    Guitarmageddon Dr. Stratster Strat-Talk Supporter

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    Those 2 larger solder blobs are grounds for the back of the pot.....

    the 3 in a row are the ones to solder the positives to, and I don't see ANY damage there.....confused?

    There's 5 spots to solder to.....
     
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  6. VMamp

    VMamp Strat-Talk Member

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    The damaged section of track can be ignored, the most important connections to solder onto are the three that are marked 1 to 3 on the underside of the PCB. Repairing this depends on whether you are going to source and replace with an identical potentiometer, refit the original or try to adapt a different type to get the pedal functioning.

    To do the repair you have to decide whether you want it as it was originally but more involved or use a simpler repair. To repair as original and without further damage will require the removal of the solder first using a good quality solder sucking tool and a 0.6mm PCB drill to clear the through plating holes.

    You will also need to remove as much solder from the potentiometer terminals, using a small file will help. Once you can fit the potentiometer into the PCB you can then solder both sides.

    By far the simpler approach and the way I would do it, would be to surface mount the potentiometer on to the top of the PCB but cut away the tag that was originally soldered to the damaged pad as this is not required since the other side is intact. You might need to shorten the potentiometer solder connections or bend them so that the potentiometer sits on the solder pads but not touching each other. You can then solder the legs onto the pads. If you have a multimeter check each connection connects to the other side of the PCB. If there is no connection your best option is to solder light gauge insulated wire from one side to the other.

    Fitting an alternative potentiometer depends on the size and type and the design of the pedal enclosure but the chances are it would most likely be better to fit it to the case and use light gauge wire and simply connect to the pads marked 1 to 3.
     
    Last edited: May 10, 2020
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  7. CB91710

    CB91710 This is a Custom Title Gold Member Strat-Talk Supporter

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    Ya, the good news is, that pad is not critical to the circuit as long as you have a good connection on the other pad.
    It is used primarily to physically secure the pot to the board.
    You can connect the replacement pot to the remaining pad, and use a dab of hot glue to physically anchor the pot to the board.

    The important thing is that the trace on the bottom of the board from the thick part of the trace to the thin part of the trace is still intact.

    If the pad on that side has lifted, then you'll need to scrape the blue coating from both sides of the pad and solder in a jumper (yellow jumpers).

    00b59431df90306d4b7675c5a43ec4da.jpg
     
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  8. StratPlus97

    StratPlus97 Senior Stratmaster

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    Ok, I think I’m understanding this now. I’m going to go with soldering a similar pot...but What exactly is the “tag” your referring to?


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  9. StratPlus97

    StratPlus97 Senior Stratmaster

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    i believe you’re confusion comes from not reading the original post.


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  10. VMamp

    VMamp Strat-Talk Member

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    The tag I am referring to is the one that was originally soldered to the pad that is now damaged. You don't really need it anyway, just remove the tag (if your replacement has them that is).

    Trying to clear 'through plating' on double sided PCBs with just a soldering iron is fraught with problems and risks further damage to the tracks and solder pads which is why I suggested surface mounting if you do not have desoldering tools, PCB drills, etc.
     
  11. StratPlus97

    StratPlus97 Senior Stratmaster

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    Ok, so the “tag” is the same thing as the “land”?
    What your recommending is removing the other tag/land, covering with solder, and surface mounting the pot? Is this correct?


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  12. CB91710

    CB91710 This is a Custom Title Gold Member Strat-Talk Supporter

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    I think he's referring to the pin/lug on the side of the pot that passes through the board.

    The three in a row on one side are the connections to the actual resistor and do the work. The other two are only for shielding, and mechanical stability.
    Shielding is provided by grounding either one.
    Mechanical stability can be provided with a dab of hot glue.
     
  13. StratPlus97

    StratPlus97 Senior Stratmaster

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    Ohhhhhhhhh. I got it! Thank you very much for the help. I really appreciate that. So do you think I need to do anything with the damaged land? From that piece coming off, does that affect the trace connection at all?


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  14. VMamp

    VMamp Strat-Talk Member

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    Ignore the damaged section.
     
  15. StratPlus97

    StratPlus97 Senior Stratmaster

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    10-4

    Thank you again


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  16. StratPlus97

    StratPlus97 Senior Stratmaster

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    Thank you thank you thank you!
    It all worked out and it’s working great!


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  17. CB91710

    CB91710 This is a Custom Title Gold Member Strat-Talk Supporter

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    It's fine on the pot side.
    On the bottom side, it carries the ground to the diode below the pot, so it needs to be secure (the right-most yellow jumper in the image I posted)
    If only the top is messed up, that pad doesn't matter.