Welding machine help needed Hobart

A couple of checks to make. First is to check where the ground lug connects to the clamp. I see a lot that come into the shop that have loosened some and arced causing a poor connection. The second is to check at the lugs inside the drive door for voltage. With it triggered you should be able to see 10-28 volts dc. This should change as you change your voltage setting. If it does also keep the meter on it while you attempt to strike an arc. If it drops dramatically then you have a voltage supply issue of a failure inside the machine.
You can run these off of a 10 awg extension cord up to 50 ft without issue. Running a smaller extension cord will work for short bursts but the longer you weld with then the more voltage drop you will have and you will see the weld performance deteriorate.