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  • Millermatic 200

    I have a millermatic 200 s/njd663237 and it won't arc everything else works like gas valve and wire feed. I've checked the selector and cleaned the contacts but am lost on what else to check so any ideas would be great also I don't have a manual for it.

  • #2
    Manuals are available on this site under the SUPPORT tab.
    Hope this is a start for you.

    Griff

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    • #3
      Help us help you.

      When did it last work? What is different now? What is your level of welding experience?

      Tell us the setting on every dial and switch. What contacts did you clean?

      As mentioned, the manuals are available on this website, and include the basic troubleshooting pages.

      The obvious question: To what is your work lead clamped? Have you tried arcing from the wire directly to the work lead clamp? Paint and other coatings, or even rust, can insulate the work clamp from making good electrical contact.

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      • #4
        As the other guys said, do you have the owners' manual? If not, you can download one here:

        https://www.millerwelds.com/files/ow...O1303F_MIL.pdf

        That should be the right one for your ser no.

        Assuming you have all the "right answers" to Mac's questions, here's the next step:

        Look at the schematic diagram on page 27, fig. 6-1. In the lower left corner you will see the diodes and output inductor. The contacts on relay (contactor) W is the most likely culprit. The magnetic coil that pulls in the contacts is located just up the page a bit; a circle with a W in it. It is possible you could also have a bad thermal sensor TP3, or a problem with contactor CR1. (Could be some other problem somewhere, but W is the first thing I'd look at) Contactor W is a common failure point in these old machines--it moves and conducts weld power to the wire every time you pull the trigger--and it eventually wears out. Look in the parts list section of the manual for a picture. If you unplug the machine and take the cover off, you will find it mounted on the right side near the front of the center vertical panel as you look from the front of the machine--it would be the "driver side" from the machine's viewpoint. It has three sets of contacts that are jumpered together. Power the machine, pull the trigger, and see if it clicks closed. If it does, it is very possible the contacts are burned or dirty and not allowing power to the wire. If it doesn't click, you either have an internal wiring problem, bad CR1, or thermal sensor, or maybe the contactor itself has died. Not a hard fix in any case. Good luck!

        Before you touch anything in there, be sure to unplug the machine and take a screwdriver with a well-insulated handle that you don't care too much about and short across the terminals of all the big "can" electrolytic capacitors on the back of that same vertical plate. They may be holding a charge after power is off and there's enough of them there to give you a good jolt. There's a bleeder resistor in the circuit to drain off the charge when the power is off, but I never trust them. It's been a while since I had mine apart, so I can't remember how accessible the capacitor connections are, but look around until you find a way to short them. Theoretically you should just be able to short the work ("ground") lead to the contact tip in the gun and discharge them, but that counts on in-between wires and connections; on a safety issue, it's always best to go right to the source.
        Last edited by Aeronca41; 12-07-2018, 10:41 PM.

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        • #5
          It quit working a few years ago so I used a different welder but it had been working fine until I went to struck an arc and just had a small spark and that was it. I checked settings and tried gun to ground clamp still nothing so it set. I was talking to a guy that had a fabrication shop and said it was probably the big 4 diodes by the fan so I pulled those and tried to check them but I’m not sure I did it right so I just let it sit. This week I decided to either fix it or junk it so it’s all back together and I’ve checked contacts at the 1-6 selector behind the front cover, the contacts on the relay that’s open or no cover on it, and all the connections inside. I pulled the gun apart to make sure the strands weren’t broken or corroded but no problems were found. I’ll check what aeronca41 mentioned and let you know what I find. Thanks

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          • #6
            I took a look at the diagram but am unsure of where relay w is on the machine but if that’s the one that doesn’t have the cover on it it seems to be working.

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            • #7
              I think you have the right part. Here's a picture. Unplug the welder and see if you can see if the contacts on W look worn or burned. Where are you located?
              Last edited by Aeronca41; 12-08-2018, 09:06 AM.

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              • #8
                I’ll have to look at it again because the part I was talking about is mounted on the other side of the circuit board and Smithton Mo

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                • #9
                  Smithton--too bad I don't go to Whiteman AFB any more-could have stopped and looked at it for you. Old and retired now. No more nights in Knob Noster, Sedalia,or Warrensburg these days.

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                  • #10
                    Well I appreciate the help regardless.

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                    • #11
                      Well I was able to look at the welder and figured out the contacts you were talking about and got excited because they looked burnt and pitted so I took them apart and cleaned them up but still no arcing.

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                      • #12
                        OK. First thing I would try is moving the "high/low" plug on the front panel to the other position, in case there's a bad connection in there. If that doesn't do it, you'll need to start measuring some voltages. Are you confident (and safe) with probing around voltages than can kill you if you make a mistake? If not, seek some help from someone who is.

                        Have to find out if power is getting to the diodes. Connect AC voltmeter probes to wires 63 (should be accessible at the voltage selector switch) and 62, which is accessible at contactor W. (DO NOT hold a probe in each hand--that makes a direct path through your heart if something goes wrong. Hearts don't like that. Use clip leads. My personal rule is "one hand in your pocket".) Make sure 62 and 63 are solidly connected to the diodes. Have someone trying to weld while you check that voltage. I don't know exactly what it should read, but something around 30-40 volts seems reasonable to me. If no or very low voltage there, try measuring the voltage between wires 61 and 62 (at W) while trying to weld. Should read zero or close to it. If you find voltage here, the contacts are bad.

                        Could be your friend is right and you have bad diodes but I'd search hard for a bad connection first. How did you test the diodes?

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                        • #13
                          I took them out and measured resistance both ways and had resistance one way and open the other but both top and bottom diodes tested pretty close to the same value so I found it hard to believe they were bad and I’ll test what you said when I get to the welder. Thank you

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                          • #14
                            Sounds like you tested them correctly. You did have at least one end of each diode disconnected from the circuit while testing right? Those readings sound correct. So, depending on what you find in the tests I mentioned, it sounds like there may be just a bad connection somewhere, in which case you are going to have to start at the transformer and trace voltage while trying to weld. When you lose it, you've found the problem.

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                            • #15
                              Ya I had them all off and I’ll let you know what I find.

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