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xmt 304 Help 0

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  • xmt 304 Help 0

    I just purchased an XMT 304 that has immediately failed. It was in a shop with 3 phase power and I had them turn it on before I purchased it and it came up with no issues. This is my second XMT 304 and I wired it up for Single Phase power just like I had my other one. It came up fine but after about 10 seconds there was a load bang and HELP 0 displayed on the screen.

    I took off the cover and there was no obvious damage so I got out the technical manual and found that HELP 0 meant a shorted RT2 Thermistor. I haven't had a chance to measure the Thermistor but wanted to start looking for parts.

    Is there anything that I could have done in the switching to Single Phase that could have caused this or is it a bad coincident. I have verified that the hook up is exactly like my other XMT 304 so it is wired correctly (and it is labeled as a Single/3 Phase machine).

    Assuming that the thermistor is bad, anyone have a good source for these? Looks like they run about $50 but was hoping to find better price if possible. I noticed several other new old stock 30K Miller thermistors on ebay but they are different part numbers and not sure if they would be interchangeable.

    Thank you in advance for any insight you may be able to provide.

  • #2
    Finally got a few minutes and was able to get the cover off and measure the RT2 thermistor. It read 54K in my 50 deg shop. Within 1 K of what the thermistor on my working XMT 304 read so it looks like the thermistor is not the problem. Guess I will have to get PC3 out and start looking for issues on the board.

    Any suggestions on where to start?


    • #3
      Have you tried calling Miller tech support to see if they can walk you through some trouble shooting to find the culprit? I have another brand machine that went boom on me, that company sent me the info and then called me and walked through the step of checking board components to identify the problem. The new board is $500, which in that realm I consider to be low. However, I just got the comments in and am going to attempt to make the repair for around $40. I hope you get it figured out.


      • #4
        If you had a loud bang most of the time the IGBT or main caps go boom pull off the interconnect board and inspect them also pull the caps to look for any imperfections.


        • #5
          I agree with Weld dr. Check the Large blue capacitors mounted behind the Interconnect Board. And while the board is off, check the IGBTs for a short or damage. The link-up contactors may be bad too, check the contact points for arc damage. That will be a good indicator of the IGBTs being shorted. You can count on the interconnect board being bad too. Get your wallet out for this repair. It gets costly real quick!


          • #6
            The contactors were only used to power this machine in single phase. Unfortunately it only takes a millisecond difference between them to over amp the unit. It is highly likely that all components on the power side are bad and if not mistaken the IGBT's for that unit are obsolete.


            • #7
              If it is the IGBTs, you can replace them with the Powerex or Mitsubishi CM150DY060 or something close (need to check my old docs...). A few of the older ones ran a larger IGBT module - you should be able to read the part number off one of the modules. Most likely you'll have to salvage the power connector board on the old modules, and be sure to check the power connector boards' components. They usually go with the IGBT.


              • #8
                So far everything checks out. Capacitors look good and measure out within tolerance. Diodes are good. I did notice a component (R250) on PC1 that did not look right. Checked out my other board it it appears to be a 5 Ohm resistor. It is open on the bad board. Maybe a wire wound resistor? I doubt Miller will sell resistors but I will call and see if they will give me the specs.


                • #9
                  Just give Miller tech the board assembly number and part number, and they will give you specs for that component. If you heard a loud bang, there is probably a power component out.

                  Also, I didn't have the right part number for the inverter IGBT modules - should be CM150DY12H.