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Thread: Miller XMT 304 HELP 0

  1. #1
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    Dec 2021
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    Miller 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. #2
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    Re: Miller XMT 304 HELP 0

    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. #3
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    Re: Miller XMT 304 HELP 0

    If you had a loud bang something failed. Before you do anything. look at the large buss capacitors, look for holes or swelling. Try removing the interconnect pcb.
    Mark the wires before removing. Check the vent plugs on the capacitors.
    Check the input diode and IGBT blocks for damage.
    A quick test is, use a test meter in diode test mode and check the input diode and across the IGBTs. Make sure nothing is shorted.
    While pcb is off, look at the contactors and AUX switch. look for damaged contacts and stuck contactor. Check the coil ohms. at the plug in the front left corner of the control pcb on top of the capacitors. should be around 7 ohms.
    Report back what you find.

  4. #4
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    Re: Miller XMT 304 HELP 0

    Quote Originally Posted by ccawgc View Post
    If you had a loud bang something failed. Before you do anything. look at the large buss capacitors, look for holes or swelling. Try removing the interconnect pcb.
    Mark the wires before removing. Check the vent plugs on the capacitors.
    Check the input diode and IGBT blocks for damage.
    A quick test is, use a test meter in diode test mode and check the input diode and across the IGBTs. Make sure nothing is shorted.
    While pcb is off, look at the contactors and AUX switch. look for damaged contacts and stuck contactor. Check the coil ohms. at the plug in the front left corner of the control pcb on top of the capacitors. should be around 7 ohms.
    Report back what you find.
    Many thanks for your detailed thoughts. I will be able to get back to it Wednesday and will report back then.

  5. #5
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    Re: Miller XMT 304 HELP 0

    Quote Originally Posted by ccawgc View Post
    If you had a loud bang something failed. Before you do anything. look at the large buss capacitors, look for holes or swelling. Try removing the interconnect pcb.
    Mark the wires before removing. Check the vent plugs on the capacitors.
    Check the input diode and IGBT blocks for damage.
    A quick test is, use a test meter in diode test mode and check the input diode and across the IGBTs. Make sure nothing is shorted.
    While pcb is off, look at the contactors and AUX switch. look for damaged contacts and stuck contactor. Check the coil ohms. at the plug in the front left corner of the control pcb on top of the capacitors. should be around 7 ohms.
    Report back what you find.
    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.

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