I don’t know anything about that piece of equipment but I would take it somewhat apart and look at it for something simple. Blow the sand and dust bunnies out. Is there a shaft with a keyway that sheared, or a broken wire, blown fuse, etc.? Maybe not, but it’s worth checking.

 

Have you searched the internet, starting with the Hobart site, using the unit model or code number, trying to find a manual or other documentation?
Just as SmokinJoe said, I too don't know that unit at all, but have a general understanding of engines and basic electronics, as do many others here. If you could post links to any documentation, or at least post lots of good pictures starting with the whole machine, the Nameplate, and its controls and internal workings, someone ere should have more detailed suggestions.
What is your background at fixing things? Do you have a VOM and know how to use it?

 

I don't know about Hobart, but a Miller has a couple of fuses inside. If they blow it affects all output.