Miller Legend DC missing

Looked at a Miller Legend NT for sale. The 60 and 100 Hz output
seemed ok (slightly low) and the AC welding output worked. There
was no DC welding output. We looked at the rectifier and found
nothing visibly wrong: Connections seemed tight, no signs of
overheating. I could not make sense of the rectifier in-circuit,
it seemed to have continuity in all directions with less than
1 V drop, but the test current is only a couple milliamps, so
it likely isn't relevant.
Has anybody encountered this problem? Google found essentially
nothing on the likely keywords. The rectifier seems available,
but the inductor (called DC-Z in the parts list) is not. Being
flummoxed I only offered $400, but the seller said he was in for
$1500 and didn't want to take the loss. I'd raise the offer if
I had a clue to what's wrong.
The welder is in fair shape: 3500 hours, starts easily, puffs
smoke on start but clears up. Oil and air filter appear to have
never been changed. Slip rings are good, visible but not feelable
grooves. Tin is beat up but complete. I'm unlikely to wear it out.
Thanks for reading,
bob prohaska
Reply to
User Bp
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Bob, is the rectifier SCR controlled?
If so, I would suspect welding control board.
I once bought a similar Trailblazer welder for cheap ($500), replaced one board ($500), spent a fair amount of my time ($XXX???), and sold for 3,500.
You are taking a risk here.
i
Reply to
Ignoramus30183
No, it looks like a selenium rectifier (stack of metal plates).
The AC welding and power voltages are ok, far as I can tell that means the control circuits are working, or at least alive. There does not seem to be any electronic control of the DC output: The rectifier and reactor are simply connected in parallel to the AC weld terminals.
That makes $2500 net, if the job tool less than three days you did ok. Or no??
Indeed, thus my question. I'd be braver if the hours were lower and it was better maintained/less-beat-up. The seller's story is a bit odd as well, saying he bought it untested while out of work, found a job and decided to sell it a year later without ever trying it. One would think he'd have been more curious.
I enjoy tinkering with old machinery but there are limits to patience. 8-)
Thanks for reading,
bob prohaska
Reply to
User Bp
Then you can diagnose it properly, do not stop thinking and complete the diagnosis.
i
The risk of the deal goes up as square of the price.
The reason is that an honest person selling something for cheap has no reason to lie. But a dishonest person selling for a lot of $$$ has a lot of such reasons.
i
Reply to
Ignoramus30183

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