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Miller 250X with too high voltage

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  • Miller 250X with too high voltage

    Greetings all,
    I was practically given a Millermatic 250X. Did a job for someone and got this in the process. Condition was reported as unknown.
    It has the digital readout.
    I wired it up. 220 single phase, made sure the little jumper tabs were set for 220.
    I set the volts to somewhere around 14 and the wire speed around 150
    I didn't have a gun for it so I put a meter across the terminals in the case and jumped the mig gun terminals.
    The feed rollers spun and the meter jumped to 35 volts. The digital readout jumped up to 35 volts too.
    When I finally got a mig gun and some wire I tried welding with it.
    Set the dials to around 17 and 220 to test it.
    The volts jumped to 30 when welding and stayed there. The arc was loud and sounded like a jet. Didn't sound like frying bacon at all.
    It was way too hot.
    Anyone had a welder with the same symptoms? Any good troubleshooting guides out there?

  • #2
    What is your level of welding experience?

    Tell us all the details you left out. What wire and size? What gas and flow rate? What polarity on the welding leads?

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    • #3
      The MM250 has a harsh arc and a very tight sweet spot, it takes time to dial it in.

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      • #4
        When you first checked the OCV with the the mig gun plug jumped it should read 30-35 OCV. It was looking for feedback and since you weren't welding it went wide open searching for it. After setting it and welding and it still went wide open either there is something wrong in the feedback circuit or the board. I'd make sure all the wires are connected to the positive and negative studs. Not just the big cables but the feedback wires.

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