Grant Erwin wrote:
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

My guess would be a shorted diode, assuming the diodes are always in the
circuit. Second guess would be a shorted secondary winding in the
transformer or a short to ground, either in the transformer or a lead
shorted to the cabinet.

John