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  • XMT304 Help7

    Hey all,

    New poster here, homeowner with limited knowledge. I picked up an XMT304 sight unseen at auction that was labeled XMT350. Unfortunately it wasn’t actually a 350.

    Anyway had an electrician run 230 for my garage and attempt to hook up the welder. He used all 4 wires to the plug where I only have single phase 230 and apparently don’t need the red wire, with the welder wired this way The welder wouldn’t boot up at all.

    So in any case I’m not sure if that or my subsequent rewiring without the red wire or if it was actually dead before it got to me but I now have a welder that will turn on but shows help 7 whenever the electrode is hot. I know this welder is discontinued but I’m hoping to get it running for not too much money.

    Here’s what I know for sure, c3 and c4 are showing 332volts. I’m not getting any reading on what I believe is c1 the main capacitor at the back of the unit on the right side. C5 and c6 are for sure smoked.

    I guess what I’m hoping is that someone can walk me through some troubleshooting to determine what went wrong and possibly an estimate to get it fixed. I paid $400 for it which seemed reasonable and i would love to get it working if possible. I don’t mind paying a diagnostic fee but if they are going to tell me it’s $1000 to replace a pcb and a capacitor I’m probably better off trying my luck with another welder. Yes I am aware of the danger that 330volts in a cap can do and will take every safety precaution!

    Thanks for any and all help!
    Harry

  • #2
    Download the service manual and run through the pre-power checklist. It's pretty good at identifying the common problems. You may need to cut the toasted noise capacitors out of the circuit if they're shorted so you can test other components.

    Comment


    • #3
      What Bushy said... You can get a version on the Red-d-Arc site (listed as the Extreme 300). Good news in my opinion, because the PCB schematics are in the manual (some variations with later versions but it's easy enough to work through) and the power components are much cheaper. My memory is foggy, but I think the torched capacitor on the input/protection board (little corner piece) is part of the SCR trigger. The input bridge rectifier has that big wirewound resistor (lower right corner) to pre-charge the capacitors, then triggers an SCR (in the Sanrex rectifier module) that bypasses the pre-charge resistor.
      When you mentioned C1, are you talking about the big metal film capacitor to the rear of the PCB? If so, t that's the tank capacitor, which blocks DC in your half bridge inverter and also creates a resonant tank with the two snubbers (small Inductors near the bottom of the interconnect board plus the diode, cap, and resistors along the bottom of your interconnect PCB). Voltages get pretty high in that capacitor, though it's AC.
      ​​​​​

      Comment


      • #4
        You have balanced cap voltage. That means you input is working. Good. bad news is you have a power board or and an IGBT problem or a PC1 problem. Any and all those problems are well into the $1000's you don't want to spend.

        Comment


        • #5
          Originally posted by jjohn76 View Post
          What Bushy said... You can get a version on the Red-d-Arc site (listed as the Extreme 300). Good news in my opinion, because the PCB schematics are in the manual (some variations with later versions but it's easy enough to work through) and the power components are much cheaper. My memory is foggy, but I think the torched capacitor on the input/protection board (little corner piece) is part of the SCR trigger. The input bridge rectifier has that big wirewound resistor (lower right corner) to pre-charge the capacitors, then triggers an SCR (in the Sanrex rectifier module) that bypasses the pre-charge resistor.
          When you mentioned C1, are you talking about the big metal film capacitor to the rear of the PCB? If so, t that's the tank capacitor, which blocks DC in your half bridge inverter and also creates a resonant tank with the two snubbers (small Inductors near the bottom of the interconnect board plus the diode, cap, and resistors along the bottom of your interconnect PCB). Voltages get pretty high in that capacitor, though it's AC.
          ​​​​​
          I was able to pull the service manual from the Red-d-Arc website and it has the pre-power checklist as mentioned above. I guess i will work through that step by step to the best of my abilities

          I did a ton of internet research yesterday before I started messing with anything in the machine. One thing I ran upon was that the tank capacitor C1(P/N 186015) is not supposed to leak its oil out. The bottom of the cap is oily and there is an oily film on the bottom of the machine where the warning stickers are for imminent death and explosion. Ive found that part available for purchase at a reasonable price but if that failed due to another part doesn't make sense to replace it for it to fail again.

          Comment


          • #6
            They all leak, from what I've seen.

            When doing the pre-power inspection, make sure to verify the big capacitors are discharged before doing any tests. If the bleeder resistors fail, which they do, they'll hold their charge for long enough that the welder could become someone else's problem at your estate sale if you don't check them before poking things...

            Comment


            • #7
              Alright slowly working through pre power list. 6-5, IGBT Modules PM1 and PM2. I didnt see any visible damage on these components, disconnected the gate lead plug from RC5. Checked C1-E1 and C2-E2 on PM1 and PM2 got 62 kOhms and 74kOhms so that passes with resistance greater than 100 ohms. Next step checked E1 to PLG5-6 and got 75kOhms and E2-PLG5-9 and got 75kOhms there as well for PM2. According to spec it should be 100k Ohms. So PM2 has failed if ive done my trouble shooting correctly. And if i was correct would PM2 result in my Help7 error code or did this failure result in more problems downstream that I need to look for?

              Thanks

              Comment


              • #8
                I wouldn't say that is correct. When the PMs fail, most likely you will see a short across C-E. Both PMs are the same - they're both half bridge modules. I will look back through the manual tonight, but think you are just confirming the gate resistors and clamping diodes aren't open or fried. Your pre-charge resistor overheated for some reason. Not sure what fails on the interconnect board that causes the imbalanced capacitors, especially since yours are reading the same voltage. If it's a board problem, there is a circuit that compares the voltages between the two capacitors and signals if they are off. You can see it in the schematic as the over/under voltage lockout circuit. It's worth checking to see if you have continuity from the capacitor through that plug. I would investigate further after completing all of the pre-power checks though.

                Comment


                • #9
                  Metro, what readings do you get on PM1? If it's 75k ohms, I would move on and assume the gate resistor values for your IGBTs are different.

                  Comment


                  • #10
                    You said you didn't want to spend money on it? If you are going to go further. Check the 20 ohm resisters on the power board.

                    Comment


                    • #11
                      Originally posted by jjohn76 View Post
                      Metro, what readings do you get on PM1? If it's 75k ohms, I would move on and assume the gate resistor values for your IGBTs are different.
                      If I remember correctly off the top of my head 62k ohms for PM1. They were not the same between PM1 and PM2

                      Comment


                      • #12
                        Metro, I guess you could get an imbalance in the capacitors if only one PM was firing (they operate as two independent half bridge inverters, one off each capacitor). But it looks like from above you are reading 332V DC on both capacitors. Nominal is 325V, so you aren't seeing overvoltage. Did you measure with the output contactor on or in remote contactor? The power modules draw a load to keep the OCV at ~84V on the terminals, so you may get an balance if only one is firing. Either way, you will need to fix the input protection board (lower right corner of the interconnect board). That charred board is conductive and could create problems. If those toasted capacitors are shorted, they may have taken out your pre-charge bypass SCR gate relay and the SCR. If you have worked through the pre-power checks and confirmed the bleeder resistors CST mentioned are not open, you can confirm you have continuity/correct resistance in your capacitor unbalance circuit
                        Bottom Cap - and Top Cap + to PC1 test point TP2-4
                        Bottom Cap + and Top Cap - to PC1 test point TP2-5

                        Comment


                        • #13
                          Originally posted by jjohn76 View Post
                          Metro, what readings do you get on PM1? If it's 75k ohms, I would move on and assume the gate resistor values for your IGBTs are different.

                          So for 6-5 IGBT Modules
                          3. PM1: c1-e1:62k c2-e2:63k
                          PM2: c1-e1:74k c2-e2: 74k
                          4. PM1: e1-plg5-10: 99kohm e2-plc5-7 99kohm
                          PM2 e1-plg5-6 75kohm e2-plg5-9 74kohm
                          6. I will have to remove the coating off the diodes d1 and d2 and check those tomorrow. I checked W1 and W2 and got 0.4Mohms

                          One thing that did happen upon initial start up was that the welder did trip my dedicated 60amp fuse in my box. One of the 120v wires in the plug was not secured down as tight as it needed to be, I opened the plug and tightened the white wire down, could that have caused a voltage imbalance. Also, after i tightened it down I opened the case and saw that the c3 and c4 caps were not torqued to spec on the negative terminals, all other bolts were tight

                          Thanks!

                          Comment


                          • #14
                            Metro, not sure why the PM2 gate resistors would read that way. Was the white wire touching one of the other wires in the plug (only reason I can think why it tripped the breaker was shorting to the hot or ground wire). Loose screws/terminals can create arcs (high voltage) which could affect your power components. Either way, it's best to work completely through the pre-power checks. So far, I am tracking overheated pre-charge resistor and two bad capacitors on the input protection board.

                            Comment


                            • #15
                              Originally posted by 1997CST View Post
                              You said you didn't want to spend money on it? If you are going to go further. Check the 20 ohm resisters on the power board.
                              I would prefer to get this welder working as a part time hobbyist this is way more welder then I would ever need and shouldn't ever need anything more except something that can do AC Tig for AL. But, I don't mind spending some money on it. I still have to buy a wire feeder and tig torch + gas but I would prefer to avoid having to spend $1000 on a new board. I can swing 200 for the tank cap and what not.

                              I tried to measure the 20k ohm resisters while they are in circuit but they are behaving oddly i think. They start showing low kohms like 3-4k and then multimeter shows open circuit and then it jump to 17k ohm and slowly makes its way up to 20ish. I dont know if that's normal behavior for a bleeder resister or if i need to isolate them to get a correct reading . The other 200 ohm resisters and 1k ohm resisters are measuring correctly except for one of the 1k ohm resisters is only measuring 500 ohms.

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