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  1. #1
    winchman is offline Stainless
    Join Date
    Jun 2003
    Location
    Thomasville, GA
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    The plasma cutter wouldn't work and the "cup" indicator light wouldn't go out. Tried replacing all the consummables and checked the cable connection for tightness. No change. The instructor asked me to "fix" it", so I commenced to take the head apart. Of course, there's no wiring diagram available.

    It's pretty simple inside. A microswitch is located behind the cup, and it closes when the cup is screwed down with all the consummables inside. I got an ohmmeter, determined that the microswitch was OK, and rang out the wires to determine which of the seven pins on the connector carried the "cup" signal.

    I couldn't get any continuity between EITHER of the wires going to the the cup microswitch and pins on the connector. By the process of elimination, I determined that pins 2 and 8 carried the cup signal. (Pin 7 on the connector isn't used.) A jumper between those pins on the machine made the cup light go out.

    I got some of the kids to help me by holding the meter leads while I flexed the cable near the head. Sure enough, it showed an intermittent open on both wires.

    Cutting into the cable, I found a burned area. Apparently several of the wires that carry the high current to the tip had heated up, and the adjacent cup wires were damaged as a result. It appeared that the problem was started by the string reinforcement wrapping being so tight that it cut into insulation on the wires.

    The best fix was to shorten the cable by about six inches, and make all new connections to the components in the head. That was done by the kids in the electrical class, and the machine was back in service about an hour later.

    Roger

  2. #2
    Mike W is offline Stainless
    Join Date
    Jan 2003
    Location
    Central Kali.
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    Good job on that winchman. A repair shop would have probably replaced the whole cable.

  3. #3
    MitsTech is offline Stainless
    Join Date
    Feb 2006
    Location
    Newtown, PA USA
    Posts
    1,378

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    What model spectrum?

    Miller is very good about putting schematics, wiring diagrams, pinouts, and troubleshooting flowcharts in their manuals which, by the way, can be downloaded in PDF from their website.

    Pick your model or enter the serial number:

    http://www.millerwelds.com/service/ownersmanuals.php

    Glad you got it fixed, but at least you will have it for next time

  4. #4
    macona's Avatar
    macona is offline Diamond
    Join Date
    Jun 2006
    Location
    Beaverton, OR
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    5,442

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    Yep, thats what I would have done. Replace the cable that is... Usually I will replace the whole torch though. You should see the condition that torches come in. Ouch!

    In my situation I realy cant afford for the machine to come back, and at $75 an hour it does not take long dinking around trying to fix a cable to justify it cost wise.

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