I have spent the last couple of days troubleshooting a pair of Canox
tig welders. These machines are rebranded Miller welders and are old
enough to be free of electronics. One of the welders is rated 300 amps
and the other at 400 amps. Even though the sheet metal on the 400 amp
one is a bit more modern inside they are extremely similar. From the
owners manual that I downloaded from Miller you can figure out what
parts are different by looking at the parts list which is very comlete.
From the manual it is clear that the 200 amp model is almost exactly
the same as the 400 amp model. What I don't understand is why Miller
would sell such similarly built machines with such a range of capacity.
Today I got the 300 amp model working, tomorrow I'll start on the
second one.

stan