| Electronics > Repair |
| TIG welder AC broke - only outputs current one way, won't switch polarity |
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| SickVic:
I have a Miller Dynasty 200 DX and the AC functionality broke. I'm not an electrical engineer myself but I have a few bright electrical friends who could help out if needed, they don't know anything about welders tho. I'd very much like to fix this welder myself, sending it off for repairs is pretty much financially unfeasible. So it broke right when I started an arc, I think I heard a pang (I think, couldv just been sound of the arc stopping), and the arc stopped and the machine gave some error. Unfortunately I dont remember what error, I just immediately switched the machine off and back on hoping it would work, but no error. It did weld but not as it should. I was welding on a 1 phase outlet without ground when it happened, and wíth the HF high voltage arc start/stabilizer. Current status: - no error codes - still welds on DC - welds like standard DC electrode negative on AC setting - so it pushes current only one way on AC, still sounds like the 150Hz it's set at, definitely some waveform, just not switching polarity - I did visual and olfactory inspection of whole machine: everything looks fine and I dont smell anything burnt, I'v been pretty meticulous I'd say, scrutinizing all components big and small - I measured the IGBTs (made sure I didnt charge a gate) and they should be fine - the two ultra fast recovery diodes in secondary assembly, marked as '2', are good - the markings on the diode thing marked as '7', I cant find it online so I dont know exactly, but it measured like a 4 diode rectifier bridge, all 4 voltage drops are the same so I guess its fine The picture is from the 'secondary assembly' which sits at the bottom of the machine. I'v added some pages from the manual. What are your thoughts? Idea's? Questions? What/where should I investigate/measure? Where could the problem be? |
| TERRA Operative:
Have you worked through the troubleshooting section of the manual? The manual looks pretty good and should narrow down the fault. The technical manual is attached below if you don't already have it, I assume this manual should be close enough to your welder to be useful. (Section 8 is troubleshooting). |
| SickVic:
Oh wow thanks! I was only aware of an Owners Manual. This should be helpful, I'll get back after looking it through and some testing! |
| TERRA Operative:
No probs, I spent a number of years repairing welders 10 years or so ago, so I still have my library of manuals. :) Let us know how you go! |
| coppercone2:
you gotta find the broken part if it went bang you can find it. This welder was a night mare for me to fix. The main thing that will beat your ass with this one is if there is scorched PCB, particularly the one with all those little 4 terminal mosfets (cascode?). I think it arcs internally or some BS if its damaged. I replaced every single parts on that PCB and it still would not work until I replaced the PCB. I guess that if its burned, its just too hard to get all the short circuit paths off, even with hours of precision sanding , scraping, cutting and epoxy+fiberglass refills in channels. I see your PCB are dirty. The conformal coating on that thing yellows and flakes, then you have dirt metal on the PCB. Wash all of them, bake them, possibly recoat them with MG chemicals silicone BRUSH ON coating (the spray is garbage) I would not be suprised if its cracked conformal coating that arced with dirt some where. Its just not durable, that welder needs cleaning as part of maintence. Ignore the people that say its OK to run it when its basically covered in rust. With what I saw going on with the conformal coating, I would remove every circuit card, do a full inspection and clean all of them thoroughly. You might find 'sunburn skin' going on. I think that design of sucking in grinder dust through the machine with air flow over PCB is nuts, IMO the thermal design is poor. I saw alot of burning near some power resistors too. They need better signal transmission lines and filtered cabinets for the circuit cards in the type of environment it goes into. I think they got some optimisitic BS from the conformal coating distributor claiming its rated for service on venus. |
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