Look for a loose connection. I've fixed lots of welders that needed nothing
more than a new lug or a connection tightened. You did not mention smoke
escaping or internal arcing so look at your connections.

Pete


"Grant Erwin" wrote in message
...
I picked up an old AC/DC buzzbox the other day. It's branded Airco and has
a red case, but it's a Miller Thunderbolt AC/DC. It's probably from 1980 or
so. I started testing it and it was welding fine but suddenly the box
started buzzing much louder than before and it won't weld worth beans any
more. I haven't taken it apart yet. I figure something could be shorted to
ground (although the 30A mains fuse didn't blow) or whatever holds the
transformer laminations together might have cracked.

Anyone got any bright ideas what to look for? I'd like to salvage this
one.

Grant Erwin
Kirkland, Washington