Machine Builders Network+ Forums Machine Builders Network Tech Resources/Skills Welding / Cutting Miller Dial Arc - DC ...Dead

My primary stick welder is a old Miller Dial Arc that I got at a school auction for $75. I have had it for about 8 years and it has always worked perfect. I had to weld something last week, I struck an arc and welded for a second, then the welder made a weird noise, kind of a low hum. Then it went away and welded fine, then it did it again and the arc got weird. I turned it off and welded it with my AHP 200X.

The next day I turned it on and it ran for a few seconds then threw the 50 amp breaker. Today I turned it on again and it did the same thing. I unplugged it and took the panels, and top off. Nothing obvious wrong inside. I hooked the meter to the switch and made sure it wasn't single phasing. it was fine.

I turned it on again and it read 120 amps. I turned it off again to walk to the other side to see if anything looked hot, I flipped it from low to high amps and when I turned it back on it sounded normal and was only reading 5 amps. I let it run for a few minutes and it stayed on and sounded normal. I turned it back to low and it still sounded normal.

I plugged the leads back in and tried to weld, the DC side seemed like it was a slow AC frequency weld. The machine seemed like it was truing to vibrate when the arc was struck on DC regardless of polarity. The AC side seemed to weld normally. I haven't used the AC side ever that I remember.

Anyway I don't have a osciliciscope but the DC leads read 290 V on AC (on the meter), and 129 with the meter on DC.

The AC side read OCV of 79.

I seems like my DC has gone out. I haven't tried to look up a wiring diagram yet. The Transformer that is hooked to the DC terminals are reading 1 OHM between the leads, so basically a dead short. I think that is normal for that. I guess I need to figure out how to troubleshoot the rectifier.

Here are some pics.

Any ideas of what to check or if it's repairable would be appreciated. I doubt it would be worth it to fix it. As it sits It is a nice AC only welder. Worst case I guess I got my money out it for $75. The sad thing is that that day I could have bout 5 of them fot $75 each....

The paint above the terminals for the AC are burnt, it has been this way since I have had it.



The transformer on the bottom is the one that hooks directly to the DC terminals. Is reads a dead short between the leads. This is with the wires hooked up, I guess I should unwire it and check it by itself.



Upper Transformers


Lower Terminal this is the one that seems to be shorted




Other side