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  • xmt350 pre-power check technical manual info needed

    I have an xmt350 that I'm hoping to get at least the pre-power check info from the tech manual.

    It will not power up. Nothing looks obviously burned.

    s/n: LG410138A

  • #2
    If you go to Red-d-Arc's website, and navigate through the support section to manuals, they're Extreme 360 is the XMT 350. They have a technical manual available there.

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    • #3
      hthttps://www.red-d-arc.com/pdf/EX360%20Service%20Manual.pdf

      Makes me want to get one...

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      • #4
        Hopefully the issue isn't in the power mods. I drew schematics for the buck/boost auxiliary power circuit and the interconnect board about a year and a half ago, will see if I can find them (two moves ago). Hopefully you won't need them.

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        • #5
          Thank you! That red d arc book seems to cover the s/n range of my machine. I have run through half of the pre-power checks and everythings looking good so far. Upon closer inspection the resistor on pc2 at the top left, R14, looks like it got pretty warm, the solder joints look nice so at some point maybe someone else was in here and let some plastic touch it when it was hot and melted a bit of that to it. Anyone know off hand what that resistor is? Looks like the ones avove the caps are bleed resistors, is r14 for inrush current?

          Why do we hope its not the power mods?

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          • #6
            R1 and R8 are your bleed resistors, R14 should be your charge/inrush current resistor. You can confirm if it is connected to those input bypass diodes on the left side of the interconnect board and either the + or - bus (can't remember off the top of my head, will need to find my schematic). Does it measure right?

            The power mods have both the input boost PFC and inverter components shared between the two of them, so you would usually need to replace them both, and the interconnect board (the gate drives tend to go when the IGBTs go). You could work through issues on the interconnect board, but the power modules are proprietary and expensive.

            One thing worth checking that's not in the pre-power checks are the bleed resistors. I had one that failed open (the opposite capacitor failed), and didn't catch the dielectric fluid on the back side of the interconnect board.

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            • #7
              The inrush resistor is 200ohms, it measures out correctly with continuity to the input bipass diodes. The bleed resistors are marked 39k the one on the right measures out around 5M.

              I turned the machine on and the r14 resistor starts smoking. I shut her down pretty quickly. No display, no fan, nothing except for the green light on the pc1 board. The only thing I have found is that bleed resistor, everything else has been checking out.

              Any suggestions of what to look at next? Haven't had too much more time to study the tech manual or poke around. Hopefully tomorrow I can get somewhere with it.

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              • #8
                Have you gone through all of the pre-power checks? Make sure you go completely through those. Also, make sure you check the voltage on the capacitors before working on anything. The total bus voltage is over 900VDC (960V if I remember right) with half that across each capacitor. It doesn't sound like your machine is getting past the pre-charge, so the bus is "only" around 325V, but still lethal. After you do, grab a light and look at the back side of the interconnect board up near the capacitors for any signs of fluid or damage to the bus capacitors. Both of those bleed resistors should measure 39k, so you will likely need to replace one, and it is an indicator that the opposite bus capacitor failed. The welder has some failsafe circuits that shut down the machine when the capacitors fail, so hopefully nothing else was damaged.

                If R14 is getting hot, then your bus capacitors are not charging to full voltage. I would assume that the bus capacitors are shorting out. Any signs of fluid from the capacitors or bulges in the cans will confirm it. They usually don't show other signs, like shorting across the dielectric, until they get to higher voltages.

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                • #9
                  Full discretion, no I did not finish all of the pre-power checks, I got most of the way through and kept getting pulled off that to help others. That hot looking r14 made me feel like those capacitors were toast, so I wanted to fire it up and see what voltages they were seeing, I didn't get that far, I just shut it off. Pulled out the caps they both test out at 1825uF and there is no sign of bulging or damage. So far that 39k bleed resistor above the right cap is the only thing that is testing as bad. I will continue with the rest of the pre-power checks to see if anything else sticks out.

                  Any other things you recommend I check that are NOT in the pre-power checks?

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                  • #10
                    That's the only one I remember. The pre-power checks said to do a visual inspection of those items, but I overlooked it on the one I fixed. Those capacitors will usually test ok with a meter, and only show their issues at higher voltages. If you think it's something else that is causing R14 to overheat, you can check whether or not it is shorted to the negative bus.

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                    • #11
                      Service Memo 1170

                      During pre-power checks, measure the resistance of resistors R1 and R8 on power interconnect board PC2. Normal resistance of each resistor is 30k ohms (out of circuit). If either resistor tests “open”, capacitors C12 and C13 have been subjected to high voltage and should be replaced, along with any other failed components identified during the pre-power check

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                      • #12
                        I made some progress, I was completely missing 2 pages from the PC1 pre-power checks. The auxiliary power circuit test values are all good (that was the only page I had). The Pre-Regulator control circuit test values shows the buck igbt and the boost igbt gate drive just high of the range, and 3 of the diodes are missing (board layout is slightly different from the picture) from my board, so I'm wondering if this isn't the correct board for this machine... The inverter control circuit test values almost all show as short circuit, one of the diodes are missing from my board off that test as well...so unless the tech manual I have is incorrect from my PC1 board enough that the tests don't work on this board (seems really unlikely that they would change the circuits that much), or this PC1 board is smoked.

                        I think this PC1 board is smoked. I have a suspicion that the caps are bad in this,(I know one of the bleed resistors is bad) I am thinking that the welder was downed and they may have had another welder that PC1 fried in and they robbed this machines PC1 board and replaced it with the smoked one. That would at least make sense why the test points dont seem to match with the tech manual that appears to cover this S/N machine, unless the red d arc machine has a slightly different circuit that the miller variant (I don't really buy that either)...OR maybe its not unusual to have missing/moved components from the tech manual? none of the 350p machiines that I have repaired had anything less or more than the tech manuals said, other than that I dont have experience repairing with any other miller inverter machines.

                        All other pre-power checks show normal (other than that bleed resistor)

                        I have no idea of the history of this machine. Only that it was not working, and it was free, so I'm only in this a bit of time so far. Is there any way with the numbers on the circuit boards to even confirm that this board is supposed to be in this S/N machine?

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                        • #13
                          Wow... not sure where to go with that without being there. Is that correct that the inverter gate drive circuit is testing short? Those are the resistors and diodes just above the right power module. Can you post some pictures?

                          You should be able to find out from Miller Tech support. Just give them the SN and the board assy number, and values of.any components in question.

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                          • #14
                            Originally posted by Popscott View Post
                            Service Memo 1170

                            During pre-power checks, measure the resistance of resistors R1 and R8 on power interconnect board PC2. Normal resistance of each resistor is 30k ohms (out of circuit). If either resistor tests “open”, capacitors C12 and C13 have been subjected to high voltage and should be replaced, along with any other failed components identified during the pre-power check
                            Thank you!

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                            • #15
                              I bid on a broken XMT on Ebay. It's already jumped to $200 which is well over my "willing to lose to play with a broken welder" threshold. Makes me wonder if there is some cottage industry in XMT refurbishing. Even working they're relatively cheap used.

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