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  • Millermatic 200 quit

    Hello, First I would like to say I have done a lot of searching and appreciate all the help offered on this site. My millermatic 200, s/n jj411271, quit striking an arc in the middle of a job last week. Got around to opening the case today and looking around. Nothing looks bad and there is no burned smell. Had been welding and went to strike arc and it just would not arc. The wire feeds normal and speed changes. The contactor is working and I replaced it about a year ago with help from the search history. I checked voltage at the contactor and got 11 vdc at the high six setting, dropped about one volt each move to the lowest setting. When I would check voltage at the bolt/connector to the gun/wire feed block it would read about -2 vdc. Dont know where to go or if that info is any help. Did check all wire connections and large nuts on diodes etc and all appeared well. Noticed that relays 2 and 3 were not energizing but do not know there function. machine is basic with no stich panel or wire feed hooked. Does use the newer 14 pin gun. ga-20c. I opened the end of the gun and the wires are clean and no sign of damage. Did have 240 vac to main switch.

  • #2
    When you measured voltage at the contactor, what did you use as a reference (ground)?

    Since it seems that the main power source is working as the DC voltage changes as you change the setting - probably best to start figuring out what is broken between the contactor and the wire coming out of the tip.

    Using the same method as you measured contactor voltage, see what voltage you get at the tip and keep working your way back toward the contactor.

    Check the simple things first - connections, grounds, etc

    Good luck and let us know what you find!

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    • #3
      used ground point where all small black wires tied into bottom of chassis. placed lead on top of contactor and then compared to bottom of contactor. Problem is I dont really know the flow through the unit. Thanks for responding

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      • #4
        I'm involved in dealing with my Mom's estate and selling her house, so unfortunately don't have time to dig in and try to help. However, I can send you the service manual--check your PMs.

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        • #5
          Gave up on trying to PM files--taking way too long. If you want to PM a mailing address, I'll mail a hard copy.
          Last edited by Aeronca41; 09-14-2019, 06:46 PM.

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          • #6
            Measuring welding volts to frame ground??? Nope.

            If you are measuring the contactor for welding AC volts... you need to find wire 62 on the contactor and wire 63 on the big select switch... Should be 12 VAC to 30 VAC from low to high and all ranges (use safe practice please)

            Output OCV of 16 VDC to 43 VDC from low to high and all ranges should be at wire drive weld cable connection and the negative output receptacle on the front.. If the DC is at those points release the drive tension or rewind wire to spool and measure from work clamp to the mig gun tip, should be the same as above...

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            • #7
              If you have OCV and no arc I would check the welding gun for open power cable

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              • #8
                Could be an open thermostat, buttered up main contactor points, bad CR1 relay. First I'd make sure the thermostat is closed. Then take the small cover off the main contactor and look at the points. Check voltage at your process switch. Some times those points get bad after this long,

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                • #9
                  Thanks for the responses. I was waiting for new voltmeter leads to come in, Old leads and no clip ends, didnt feel comfortable. Well test some more soon. Again, thanks for the help.

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                  • #10
                    Got my new leads with clips today. Got the AC circuit checked, at leads 62 and 63 I get the full range of readings (12 - 30). Went to do OCV check, lead on rear of negative lead and lead to wire feed roll. No voltage. Diodes ? Transformer check?
                    As a side note: Today I noticed the two of the leads from the stabilizer(edited to say transformer) to the range select panel were touching and had overheated. One lead had completely overheated the yellow insulation from end to end, (went to #6 on the selector). The other lead insulation was only charred where they were in contact, (went to high , if I remember right). I separated them before doing the ac circuit check. Could this have caused transformer or diode issue?
                    Last edited by cbailey56; 09-21-2019, 03:30 PM.

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                    • #11
                      Do you have 16 to 42 VDC at these points... (Use safe practice).... if you do ... unplug machine ..., remeasure the cap voltage (same points) to make sure they are discharged (if still charged look at R16 or wiring) ... if discharged then measure ohms from wire 65 on right cap strap to drive wire feed housing to check the stabilizer. (which you pointed out in post #10)
                      If you do not have the DC on the caps then you need to go back and look at the big rectifiers and diode check them.
                      Last edited by Popscott; 09-20-2019, 08:16 PM.

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                      • #12
                        Performed vdc check on caps as per photo in above post. No voltage. Did diode check. unhooked all diodes from frame. Bottom two had current one way but not the other. Top two had no current flow either way. If they both failed and need replaced is there something else to check before replacing and applying power? Thanks for the step by step.

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                        • #13
                          Want to say thanks to AERONC41 for mailing me a few pages from the service manual. In the process of reading and trying to understand flow through the machine.

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                          • #14
                            Click image for larger version

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ID:	602378 Sorry, need to correct post #10 concerning the burned insulation. I said on the stabilizer but meant on T1 transformer. Will try and upload 3 pictures to better explain. Click image for larger version

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                            • #15
                              Any progress? In your second picture, what looks to me like the voltage selector switch (but I can't tell for sure) seems to have its contacts burned from loose connections? Is that in fact the voltage switch?

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