Fixing a Problem on the Miller Spectrum Plasma Cutter
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  1. #1
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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

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  3. #2
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    Good job on that winchman. A repair shop would have probably replaced the whole cable.

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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

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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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    Similar issue, Spectrum 625 w/ ICE-40C Torch: got air, but no "spark"

    Mostly a flashing cup light, and I seem to get a solid light the more I mess with it.

    Tried the jumper, got rid of the solid light until I can figure out the flashing light. Looks like the solid light is just for the safety switch anyway. (I know it's important, but I have a bigger issue at the moment)

    -Changed the consumables, that weren't installed correctly (yup, not too tight)

    -(white) electrode wires test continuous as a group, but I'm not sure how to test individual wires without a ton of cut/splice

    -(red) pilot wires test continuous

    -(purple, orange, lt. blue) trigger/cup switch wires test continuous.

    -haven't found any blown capacitors.


    Anyone know what voltage is supposed to be going through these wires? I'm reading less than 2 VDC. I also set up the machine where I can "test" by myself while "wiggling" the cords. no change. A student told me they heard someone ran the hose over with a welding cart a year or 2 ago, which seems very possible.

    thoughts?

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    Default Thank you. even after over ten years you post helped me !

    Quote Originally Posted by winchman View Post
    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


    Same problem (well close) a quick search here and you saved me a heap of trouble

  9. #7
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    You are lucky. Mine broke, and, after finding there was no continuity INSIDE the torch, I checked the wires from the torch to the plasma cutter- they were fine.
    The torch on mine, an older non-miller machine torch, was potted in epoxy. So the broken wires were unfixable.
    I had to have a new torch made for it, took almost 2 months, as that particular model of plasma cutter (not a miller, an older Thermal Dynamics) needed a special configuration.
    Plasma is hot- 40,000 or so degrees- so it tends to wear out cables faster than, say, a radio would.


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