I bought a brand new Miller diversion 180 and brought it to school to test it out since they have some 220V plugs in the work shop. I welded some steel maybe a 16th thick very nice looking welds very easy to set up and easy to use. I then tried some thicker things and everything was good even up to 1/4 inch material at about 150 amps.
I then tried to weld some aluminum (which i was horrible at) This stuff was maybe again 1/16 thick. I was welding at 70 amps.
As I was welding I heard a popping noise from inside the machine and the 30 amp breaker blew. Strange. I reset the breaker and decided to just switch to steel. Everything seemed OK and it seemed like an isolated occurrence.
I brought it home and showed my brother how to weld a bit. No problems. Total welding time on the machine so far was about an hour.
I got a job from my neighbor to weld a steel railing, so I brought the machine back to school to use the 220V. I welded a bead 1.5 inches long at 150 amps and then I heard loud popping noises from the machine. So loud that people in the office came to see what was wrong. The breaker blew, I reset it but the machine was completely dead.
It is currently being repaired.

I am worried that I'll have problems down the line, and that my 2000 dollar investment is going to go up in smoke. I was wondering if anyone had any thoughts as to what happened inside the machine or similar experiences.
Why would a brand new machine fail in such a manner?