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Millermatic 130 Autoarc Wire Speed control Problem

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  • Millermatic 130 Autoarc Wire Speed control Problem

    Millermatic 130 Autoarc Serial# JD695831

    My wire feed adjustment has stopped working. the wire speed is stuck on high so you can only weld at maximum voltage. I have allot of 12 volt automotive diagnostic experience, but this welders circuitry is a little beyond me. I think I have a control board issue but I would like to be sure before I send it out. I am hoping someone who knows these machines will be kind enough to help me properly diagnose the problem. I have attached the wiring diagrams and below is a list of what I've checked so far. Please, if you tell me to check something, explain what I'm looking for and what I should expect to see.
    Thank You!
    Jeremy Loveland

    Motor control board output:
    measuring between plugs A & B on the control board I found 42 volts DC no change when rheostat is turned.

    Rheostat:
    I unpluged the control board connector & measured resistance between pins J & H and H & J. I have a smooth 0 - 1000 ohms when the wire speed knob is turned.

    I disconnected the rheostat and checked the wires for voltage. I was looking for signal voltage to the rheostat like I would on an automobile throttle position sensor. But I don't understand what I measured. I placed my negative lead on the welder frame and made these measurements with the wires disconnected from the rheostat.
    Wire 45: 20 volts DC & 27 volts AC
    Wire 46: 8 volts DC & 27 volts AC
    Wire 47: 8 volts DC & 27 volts AC
    Attached Files

  • #2
    Posting the diagrams is silly,

    Never the less, replace Q51 on the motor board

    Comment


    • #3
      Thank You Cruizer!

      All Fixed! I got a replacement transistor from digikey delivered for under $10 and now all is right with the world again. Thank you for your help Cruiser!

      Comment


      • #4
        At least he gave us a lot of pertinent information!

        a-

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        • #5
          True, but on this machine, telling me that the wire speed was stuck on high kinda gave it away. The rest of the info, I didn't even read. i had to pull up the motor board circuit diagram to figure it out to what was wrong. the pull out Q51 transistor seemed the logical choice, and sure enough it was.

          So yes, its good to have some info, but too much isn't a good thing either.

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          • #6
            Jeremy. What was the part you got to fix your issue?

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            • #7
              And Cruizer, where can i order a Q51 transistor?

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              • #8
                Was quite a while ago, I'm surprised I'm even still alive, but Digikey or Newark

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                • #9
                  I can't find anything listed as Q51 transistor

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                  • #10
                    Q51 is the circuit designator on the board, not the part number. Transistors are Q and a number, resistors are R and a number, etc. you will have to find the Q51 label on the board then look at the transistor and get the mfrs part number from the component itself.

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                    • #11
                      Thanks

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                      • #12
                        Did you find it?

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