I had a very similar problem on my Miller plasma cutter. Circuit board would cost about a thousand bucks. I contacted Miller to get some deeper troubleshooting information. Turned out to be a 5 dollar transistor with 20 bucks shipping On internet. I tried it and fixed it. It pulled away from a heat sink and cooked. Might be worth calling Hobart to get more technical troubleshooting information? I was very lucky.10 years ago I bought a Hobart 12ci. I used it maybe a dozen times, and kept it stored on a shelf in my shop so it still looks like I just pulled it out of the box. I put it to good use the past few weeks working on things like making the Equal angle hitch for the mower, and a few other projects.
Last weekend I was cutting off the axle brackets on a cart with it and it quit working. Last Friday I opened up the case and found the reason is due to a burned circuit board. I contacted Hobart support and found out a replacement board cost $2,308. This unit cost me $740 brand new off the shelf and I can replace it for $650 with a newer model.
Reason for this post is not to complain, but to find out what others have for plasma cutter? Other brands, and how they held up.