buzzbox blues

Aug 13, 2005 12 Replies
G

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


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P

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

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G

It buzzes loudly regardless of whether any leads are plugged in at all.

If it had any capacitors I'd guess they shorted. But it doesn't. I'll pull the cover as soon as I can.

GWE

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J

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

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B

Sounds like it burned through some insulation and made some shorted turns. Those boxes are only good for a 40% duty cycle and overheating ruins the winding insulation. Probably need to chuck it or try DIY rewinding. Bugs

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G

Pop the case and look on the right side for a main bus ribbon that has melted in half.

Gunner

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G

oooo..yah...that could be it!

Gunner

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M

Is it a arc point to point that wore down and once jumped it makes plasma and dumps. Might be a matter of adjusting for the wear of he points so it does it normally.

Just a thought - might be it. Can't think of the 'real name' it is a gross form of a regulator.

Martin

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G

I tore it down today. First I ran the shunt all the way down and back up again, then I wiggled every heavy wire. All looked good. So I plugged it in and no more bad buzz. Didn't try running a bead yet, but the main symptom has gone. Rules out a shorted diode. If it starts again when I'm actually running a bead, I'll figure it's a thermal related issue with a transformer winding. Thanks for all the tips, excellent help!

GWE

Randy Zimmerman wrote:

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