Maybe your screwed, not sure. I have a PowCon MST 300 230/460. The
manual says the for my model there are 3 input voltages available,
230/460, 380, and 575. To change my input voltage i needed to open the
welder by splitting open the shell and then there is a circuit board
that needs to be flip upside down 180deg and then rearrange the 4
studs.

I scanned the relevant page and put it here. Sorry didnt have time to
shrink it down, about 1.25megs. It's not going to be up long. email
me if you want it sent directly.

http://tinyurl.com/dcnch

Aloha, Russell