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Thread: Miller XMT 304 Repair

  1. #1
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    Miller XMT 304 Repair

    Hi
    i'm just starting to try and fix this welder and looking through it to see what it is like and what parts i may need.I think the input rectifer is missing or i thnk thats what it is called.I'm going to post up some pictures and would love if preople could take a look and tell me what they think.The weler was broke when i got it so it has never been running I only have it a week or so and i'd like to give it a go to get it upa and running it will be good practice for me and im really intereted in learning things like that. The welder looks well stripped because i was taking some parts off it for another one but i have some parts there to build it back up apart from the input rectifer.Even after putting that back on it might not run but i want to try it anyways.

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    Last edited by mandylad; 11-23-2020 at 10:06 PM.

  2. #2
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    Re: Miller XMT 304 Repair

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  3. #3
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    Re: Miller XMT 304 Repair

    Also the capasitors that are in it aren't the original ones they are big blue ones.the original ones are white is that correct?
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    Last edited by mandylad; 11-23-2020 at 10:26 PM.

  4. #4
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    Re: Miller XMT 304 Repair

    Now that you have the interconnect pcb. make sure you check the two diodes on the bottom left and the two brown resistors. The vertical brown resistor is known to fail if the right capacitor fails. If one of the diodes are bad the IGBTs are failing.
    then check IGBT blocks with diode test should see a diode between 3 of the terminals. white capacitors were used on the older welders. You might be able to tell how old they by decoding the markings on the capacitors. we like to change them when they reach 7 to 10 years old. Make sure you are static discharged and measure the gate leads to the IGBTs. should be 100k. These are the only tests you can do to an IGBT with out an IGBT tester. Miller sells one, you can down load the owners manual and build it from the diagram in the back.

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  6. #5
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    Re: Miller XMT 304 Repair

    i am missing a piece..its the SR1 is it? it sits beside the IGBTs just in behing the interconnect pcb.Where would i pick up that part?Ebay?would you know of a replacement part that would suit it?
    My machine is 3 phase 400 volt.

  7. #6
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    Re: Miller XMT 304 Repair

    What size are the little capacitors that are connected to either side of the positive and negative terminals
    Last edited by mandylad; 11-24-2020 at 09:59 AM.

  8. #7
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    Re: Miller XMT 304 Repair

    I checked the caps and they seem good. I tested the IGBTS aswell they seem good too.see when you replace the Igbts do you take the little pc board of the old one and solder it on to the new ones?. See the black D1 and D2 diodes what should they read out at 2000 ohmns??when checking them do you put the multimeter on to the 2 little legs sticking out?or do you put the meter on one leg and the other end on the bolt in the middle of the diode?do i set the meter to ohms or diode test?Im getting 2 different readings from it when i do it on ohmns. If i attach the multi meter to the 2 little legs on the diode it reads just over a 1090 ohms i think and if i swap the positive and negative over on the legs i get over 3200 ohms. Idont know if im doing it right.
    I need to get a input rectifier for it to see how it goes..Do you know where i can get one?I see them on ebay they seem very cheap i just want to make sure i get the right one.

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  9. #8
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    Re: Miller XMT 304 Repair

    ive put upsome pics of the multi meter readings from testing D1 and D2.Please take a look and let me know your thoughts

  10. #9
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    Re: Miller XMT 304 Repair

    your meter has a diode test mode. place selector in the ohm position and press the yellow button. shorted lead will now beep. On a diode place the black clip on the cathode end (stripe) And red clip on the anode end (< )diode symbol -I<-.
    A good diode will read between .200 and .800 depending diode type. reverse connections and it should be over 1.2 to OL.
    Look in a different XMT for the input diode spects. or order a new one from a Miller supplier. If you buy a IGBT from Miller they come tested and graded to work as pairs.
    the little pcb comes attached. If you buy on open market or directly from powerex it will come with out the filter pcb and will not be graded. may or may not work right.
    Could blow up.
    For testing of the IGBT look at the label on the side. you will see a diode that is parallel to a transistor. you can test the diode and if it is ok, the transistor (IGBT) is ok most of the time.

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