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Vox Pathfinder 15R head hum - not output

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  • Vox Pathfinder 15R head hum - not output

    There is a constant hum, volume control does not effect it. Looking at the schematic and PCB - VR4 is the master volume and since that does nothing it's gotta be after it. Looking at IC4. I tested the voltages and they are as follows:

    1: 0v
    2: -2v
    3: -20v
    4: -2.3v
    5: 20v

    This seem correct?

    Click image for larger version  Name:	full?d=1349532940.jpg Views:	3 Size:	146.3 KB ID:	910903
    Last edited by beedoola; 08-09-2020, 04:48 AM.

  • #2
    Real TDA2030 are hard to find, but LM1875 fits, I'd try one.
    Education is what you're left with after you have forgotten what you have learned.


    • #3
      Pin 4 of IC 4 must be around zero.
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      • #4
        When attempting to diagnose a fault on these 'all in one' output ic's I find it best to look at the input signal going to the IC..
        If the power rails are good & the input is good but you have a bad output, it is highly probable that the output IC is bad.


        • #5
          Temporarily disconnect the reverb at W4.
          Improvised solder on W4 connector, cable with 6.3 mm female guitar jack.
          Connect the guitar to the 6.3 mm jack.
          Set the VR4 on 5 to 8, and VR7 to max.
          If you hear a clear and loud guitar tone the IC4 (TDA2030) is correct.
          Who does not know and knows that he does not know - teach him Confucius)
          Who knows and does not know that he knows - wake him Confucius)


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