Okay, since you say it's an older unit, I'm going to take a risk and assume it's not an inverter rig. Thus, it has a transformer. If the thing is blowing the fuse the moment you strike an arc (pull the trigger), but not when you first turn it on, then the transformer is probably okay. The most likely cause is then a short between the contact tip and ground, after the contactor relay. So, I'd say it's time to replace the liner, the adaptor and the tip, and check the wiring in the handpiece while you're in there, just to make sure you don't have any cooked insulation that might be exacerbating the problem.

Best guess I can come up with, Will. Hope it helps.

I am going to guess that you have an inverter type MIG. These would be less than half the weight of a transformer MIG.

The inverter type MIGs are rather more complex than a transformer MIG. Unfortunately, my guess is that the electronic card that does the switching is the problem, or possibly the big power switching Mosfets, or whatever they are using to generate and control the voltage.

If this is an inverter unit, and you have not been able to figure it out, it will probably need to go to a professional.

As to whether it is worth fixing, it comes down to the estimated repair price, the price of a replacement unit, is the unit a quality unit, does the unit meet your needs, how old it is, etc.

Richard

http://www.fergusonsculpture.com
Sculptures in copper and other metals