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Spectrum 875 blew up PM2

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  • Spectrum 875 blew up PM2

    I have a Spectrum 875 Autoline that has roached PM2 (inverter IGBT module). Blew the side out of it. The machine was used in an industrial setting on 460v. Probably pretty nasty power, outside, in the summer. It came to me with the amps maxed out and the switch on "gouge". Does anyone know of common collateral damage or probable causes when PM2 goes bang? I can probably work my way through troubleshooting the board, I have experience with inverter technology and power electronics, but step one is always asking folks who probably know more than me. I am also willing to purchase the any sort of tech manual that goes with it. I don't want to just slap a $350+ IGBT module on and burn it down.

  • #2
    I would call Miller first...Bob
    Bob Wright

    Spool Gun conversion. How To Do It. Below.
    http://www.millerwelds.com/resources...php?albumid=48

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    • #3
      I second it. You mentioned maxed amps and set to gouge? What does the working end of the torch look like? Did they try replacing consumables before you got the sweet deal?

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      • #4
        I guess it could have been consumable related, but PM2 was burned down hard. I went through the interconnect board and checked every single resistor/diode/transistor and found no issues anywhere. Hopefully I will get back to it in the new year.

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        • #5
          There is a list of pre power checks for this machine. I would check everything before I just replaced PM2. It is possible to over amp this machine using consumables passed their useable life. It really puts pressure on the whole machine. Maxed out and in gouge shouldn't bother it. That's what they are engineered to do as long as you change consumables.

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          • #6
            If the inverter module went, it likely took the gate drive with it, so you would want to check those components. There is also a possibility that it took out the bus capacitors and the input boost converter too. Have you gone through the pre-power checks like CST mentioned. Those may also indicate why the inverter module failed.

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            • #7
              It looks like you already checked every diode and transistor separately, so the long paragraph below may not be helpful. I think testing your power supply (flyback board) with a current regulated power supply.

              Looking at the signals between boards, the 875 has a boost PFC circuit, and a half bridge inverter with active snubbers. If you locate the boost IGBT and diode, make sure they're not shorted. You can do the same on PM1, which is the input rectifier. There are probably one or two pre-charge bypass relays on PC2, could be 30A relays because I have seen those pop up on a lot of welders' board. Check the traces underneath for signs of over current. When PM2 went, it possibly caused a fast discharge on the bus capacitors. I can't see them in the opman parts list, so they're probably soldered onto PC2 - check for signs of damage, either puffy at the top or dried fluid around the bottom. It's worth checking PM3, which looks to be the output rectifier, as it may have been the cause of PM2's failure. Confirm the resistances on the gate drives to make sure they're not open on the gate drive, and all gate circuit diodes are ok. The flyback driver board looks to generate all power supply voltages for the controller, so it's worth ensuring the output voltages are right. I think the bootstrap circuit comes from RC27 on PC2. The Miller Dynasty 200 (search Dynasty low buss voltage) uses a zener on PC2 to make that 15V, I bet the 15V on PC2's RC27-4 is made the same way.

              Hopefully you get a technical manual and hopefully this helps.

              Jon
              Last edited by jjohn76; 01-04-2020, 08:53 AM.

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              • #8
                Thanks. I think I will start and work my way all the way through again. Something had to cause the failure. I refuse to pop a new module on without finding it.

                In other news I scored a free 2050 that had input/rectifier board issues which were easily resolved. As soon as i get a torch for it that belongs to me, i should be good to go on that unit.

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                • #9
                  Great news! That 2050 machine is more fixer-friendly. I had to work through the PFC boost converter board and the main PCB on a couple of them so far - schematics are available, which was a huge plus.

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                  • #10
                    yes definitely. I could build a 2050 from scratch if I really was glutton for punishment. It wouldnt work unless you banged on the case really really hard. (i was never able to replicate this "fixed" mode). The power light would just flicker rapidly and the main contactor never pulled in. I pondered for a bit and remembered a lot of VFD inverters precharge the bus through power resistors before using a contactor or SCR to light up the rectifier. Low and behold, had one of the ceramic block resistors that was open.

                    the 875 is quickly approaching not worth fixing for me. I see bare working units for sale here (no torch, and I have a torch and all) for ~$1k at times. I am hard pressed to spend $400ish on the igbt module, then atleast $500 more on it at a board repair house (or $1k for a new board). It sucks because its such a nice bit of kit.

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                    • #11
                      Yeah, if you do decide to fix and power it, I wouldn't test it with power without a pair of light bulbs on the input. The spectrum 625 had modules soldered directly to the board - not fun and very tough to source...

                      Funny you mention building one from scratch. I am not going that far, but have a 460V Hobart Portatig I am looking to resto-mod at some point - dual interleaved DCM PFC boost input, new inverter module with drivers triggered by the existing control, auxiliary power circuit (unless I can find the right transformer to rewind for cheap), and an inverter output. Just about everything is on hand, just looking for time... Resto-mod POWCON with litz wire secondary and 800-10000Hz variable frequency FPGA control after that...

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                      • #12
                        This one uses Mini skiip 3/2 power modules. They are proprietary parts in a standardized case. No datasheets available. The primary interconnect is not a super complicated board. Those are the only proprietary parts associated with the board and they bolt on. At some point i will draw a schematic.

                        speaking of crazy projects. I have most of the stuff over here to build a square wave H bridge for tig use.

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                        • #13
                          I gave up on a Spectrum 625 because of that. Let me know when you plan to start that output inverter project. It's on my list, but the project queue is high and everytime I am about to start mine, I suffer from paralysis by analysis...

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                          • #14
                            Originally posted by raven007 View Post
                            This one uses Mini skiip 3/2 power modules. They are proprietary parts in a standardized case. No datasheets available. The primary interconnect is not a super complicated board. Those are the only proprietary parts associated with the board and they bolt on. At some point i will draw a schematic.

                            speaking of crazy projects. I have most of the stuff over here to build a square wave H bridge for tig use.
                            Were you thinking of integrating HF start with that H-Bridge? I have seen a couple AC tig units that have a touch start option, just wondering if it contaminates the tungsten or the weld.

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                            • #15
                              Yeah. Although after starting you don't need it because the arc spends so little time at the zero cross. Sine wave AC TIG tends to need it to keep the arc lit as the arc voltage rides the sine and spends a comparatively long time below arc sustaining voltage.

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