MM350P woes, blowing IGBTs

Tue, 31 Aug 2021 09:35:52 GMT

go to see Welding Machine for MM350P woes, blowing IGBTs

Bought this as a nonworking unit.  Serial LF054480 Stock 907300.  200/230/460 volt unit configured with moveable board and wire connector to 230V, connected to a single phase circuit providing 245ish volts.  Originally throwing error code 3, not on startup (that would indicate shorted trigger switch) but when trigger was pulled and held for more than 2-3 seconds.  Voltage output of 0.00 on the display when trigger pulled.  Called Miller, had a tech tell me to measure resistance between white/black wire pairs going to IGBT’s, had one pair at about 10 ohms which Millers tech told me was a shorted gate on an IGBT, replace the pair.Go to LWS, spend a chunk of change to get 2 new IGBT’s, Miller PN 212936.  Install in welder using ground wrist strap and everything.  Power back up, now when I pull trigger I get 40-50 volts OCV on the display.  Go to try and lay a bead (.035” wire on steel plate, 75/25 ar/co2 mix shielding gas), as soon as wire touches the surface I hear a loud “POP”, no arc and welder goes back to 0 OCV on display (and measured with meter) across output terminals.  Hold trigger, get error 3.Call Miller again, different tech this time tells me “oh yeah anytime you replace the IGBTs you also replace interconnect board” great, that would have been real useful information before I blew out a $330 pair of IGBT modules.Before I blow even more money on a new interconnect board and another pair of IGBTs I want to make damn sure this isn’t going to happen again.  So viewing another thread on the miller boards I saw some information to check regarding other components.Capacitors read infinite ohms one way, dead short the other.  Connecting red to + and black to the other terminal and putting meter in cap test mode I get ~2450 uF when the label says 2700 uF @ 450 VDC on the capacitor.  Cap vents appear fine and caps don’t look swelled.  Is this value within tolerance?Checking SR1 with diode tester on my DMM I get .43-.44V across all 6 diodes.  Whats the spec on this?  Nothing from any terminal to backing plate.Anything else that can go wrong, before I make another IGBT go pop and then curse a lot?
Replyrobably dont want to hear this but you need to carry it in to a repair station and let someone who knows what they are doing fix it.Millermatic 350P/Python/Q300Miller Bobcat 225NT Syncrowave 250Coolmate 3Millermatic VintageHypertherm 1000
Reply:Originally Posted by GlidertowProbably dont want to hear this but you need to carry it in to a repair station and let someone who knows what they are doing fix it.
Reply:I have never seen the insides of a 350P, so I can't say specifically what to look for.  There are usually zener diodes of 18v or thereabouts at the gates of IGBT's to prevent transients, and full wave bridge rectifiers near each IGBT with their attendant caps.  Those usually need to be checked if the IGBT blows.  If it was my welder, I would try to get the specs on the IGBT's or better yet, the makers part numbers and buy them wholesale from DigiKey.Last edited by DougAustinTX; 09-28-2016 at 07:10 PM.Reason: added useless verbiageMiller Syncrowave 350Millermatic 252/ 30A spoolgunMiller Bobcat 225g w/ 3545 spoolgunLincoln PowerArc4000Lincoln 175 Mig  Lincoln 135 Mig Everlast 250EX TigCentury ac/dc 230 amp stickVictor O/AHypertherm 1000 plasma
Reply:I don't see how you can possibly troubleshoot this issue correctly and efficiently  without a schematic. You really need the test point locations and voltages at test points.When i grow up i want to be a welderPRIMEWELD TIG225ACDCPMillermatic 215Everlast PowerPlasma 50oxy/acNot enough talent to use any of it very well
Reply:I have a 2004 MM350P that I just ordered a new interconnect board for. It didn't originally come with Hot Start and just ordered new board to upgrade would sell old working interconnect board if you're interested. Doesn't have Hot Start though.
Reply:Originally Posted by DougAustinTXI have never seen the insides of a 350P, so I can't say specifically what to look for.  There are usually zener diodes of 18v or thereabouts at the gates of IGBT's to prevent transients, and full wave bridge rectifiers near each IGBT with their attendant caps.  Those usually need to be checked if the IGBT blows.  If it was my welder, I would try to get the specs on the IGBT's or better yet, the makers part numbers and buy them wholesale from DigiKey.
Reply:You might see if you can get the tech manual for your machine. Should have a prepower check list.
Reply:Originally Posted by greenbuggyThe IGBT modules for this machine have a circuit board attached with the zener's, a couple resistors and plug to connect the gates to the wire hooking them up to the main control PCB.  So without busting out a soldering iron you can't replace the IGBT's without the zeners that are *supposed* to protect them.  The IGBT's are CM75DUM-12F but Digi-Key has no ref for that.  I can find some on eBay but given their location (China) and cost I worry that they are knockoffs and I'd rather be welding than messing with this thing.  I did check caps and the rectifier module and hoping someone can tell me what the test specs are for them.Got a schematic both in the regular manual and on the inside cover of the machine.  Many components values on the IC board are specified right there on them but I'm going to be replacing the whole thing anyways....my bigger concern is if there is another issue that could be causing the IGBT's to blow I don't want to spend hundreds more dollars to find out I missed it.Captain, PM sent.
Reply:All you need is the tech manual, which will give you a detailed pre power check to perform before you do anything else. The problem with inverter repairs is that unless you have some familiarity with them, and know what to check, you're wasting your time and money. I'll email you a tech manual for it. PM me your email address. I may still have it from the chuck purchase, but I'll have to look. You'll want to do ALL the PP checks before you go any further. Still no guarantee, but if you have checked the traces and resistors on the interconnect board and they check ok, it's likely good. Miller tech service is often going to give you an "out of the box" response in regards to replacing parts. It's often a guessing game from their end too and without being in front of it, it's hard to nail down the specific problem. Don't expect a slam dunk solution from them in most cases. I've had even some of the experienced guys there be completely off on stuff I later discovered the problem to.Honestly, ccawgc is probably your best bet as far as solid, reliable technical advice on these machines goes. I would PM him and explain the problem to him in detail. He's one of the best techs I've ever come across, and I've spoken to a few. If he can't help you, it's probably not going to be worth it to fix.I may have a set of power modules for you. I'll have to cross reference them with that machine and see if they're the same. They came out of an Invision 456P. I know they're similar, being all the newer Miller inverters of this style share similarities in their basic operating platforms.Last edited by 7A749; 09-28-2016 at 09:48 PM.Expert Garage Hack....https://www.facebook.com/steven.webber.948