Miller XMT 350 CC/CV won't turn on

[capeterson98]

Hi all,

I'm trying to diagnose a problem with my nephew's Miller XMT 350 and am hoping someone on here might be able to give me an idea where to start looking. The welder worked fine when used last then the next time would not turn on. It's wired up 220 Single Phase and has no burnt parts, no burnt smell, or bulged caps. When switched on, I measured 220 on the wires coming out of the switch. I'm thinking a relay maybe, but don't want to start tearing it apart until I have an idea where the problem might be. I have experience fixing TVs and various other types of consumer electronics in my spare time, but I'm no expert. I would appreciate any input.

Thanks

[AGW]

Hope this isn't your case, but I had one at a customer of mine that did basically the same thing. They used it one day and came in the next morning and splat, nada, nothing. Using our tech's terminology, it had a "catastrophic failure" chain reaction, 4 or 5 things went out. Estimate for repair was almost $3000.00
Hope your luck is better.

[ccawgc]

The XMT 350 is a different system. There are very dangerous voltages inside the case when it is operating. It is a auto line machine. It takes any voltage between 200 and 600 AC in and makes around a 900 volt DC buss. 470 volts on each large electrolytic capacitor. First thing you can do is remove the cover and look at all plugs and the modules behind and below the caps. Shouldn't need to take anything apart at this time. If the input module fails it usually explodes and black soot will be on the case and pcb. See your private messages.

[ccawgc]

Second thought. Make sure the wires in the plug are connected right and are tight. Then go to the line switch. If those are good proceed to instructions above.
You would not believe how many welders come in with complaint " will not turn on" and the only problem is loose or disconnected wires in the line plug.

[capeterson98]

My nephew tried a second plug to be sure it wasn't the plug or wiring. He gave it to me without, so I added a plug to allow me to plug into my 220 dryer outlet. The power in this thing definitely makes me nervous. I always Check large caps before I touch anything. No soot and connections all tight. I'll post some pics later today and I'll respond to you message ccawgc later today.

[norrijdn]

Did you find the problem? I have one doing the same thing.

[ccawgc]

see post 3 and 4 the reread #3. Beyond making sure you have line voltage into the pcb, Might require a repairman.
PC boards get real pricey and there is no warranty on the pcbs if installed by the owner.
I would not want you to spend $1000 then blow it up and have to spend that again and more.

[SPO]

I have a similar problem. I bought a Miller xmt 350 mpa, and found out that it has a blown resistor r14 on one board shown in pic, and a missing component on the other board circled. I need help from anyone, identifying the values, and names of these components. From the looks, the caps seem to be in good condition. So I'm thinking the resistor is the only thing that blew. If anyone thinks, or knows from experience that something else might went bad, please let me know..