I still have no real idea on what caused the failure of the transformer and switch.? I just replaced the parts and hope for the best, with the lurking feeling that it will happen again.? I now do have a better delta connected surge protector installed at the AC mains plug.? No issues so far with very limited use.
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Before power-up, I checked that the fuse was the proper rating.? ?I didn't check when I bought the used machine.
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I tore down the faulty switch.? The copper colored stud contact is damaged where the brass colored spring loaded tab makes contact.? It looks like there was arcing in the switch as the 'copper' has migrated.
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I cut away the faulty transformer's insulation tape, and it did not have a thermal fuse.? None of the visible magnet wires showed sign of damage.? I have not yet unwrapped it to see if there was a possible arc over on the primary before becoming an open.?
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One idea I had was to not switch any 120V AC through the pot/switch.? Rather switch low voltage DC as the control input to an optically isolated relay (low voltage, low current through the pot/switch).? This circuit could use either the unusual as-built pot/switch which is closed when CCW, or the much more common open when CCW.? ?The 12V fan circuit _might_ be able to supply enough extra current to power a relay.? I've used relays such as in the past.? Had LMS not had the pot/switch in stock in a reasonable time, I would have done this.? ?I mention this alternative in case someone else is having issues with their pot/switch and can't find a suitable replacement.? As much of this post is only in the spirit of sharing my findings for others to find, and if someone has more insight... I'd be happy for them to share with me.
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Regards,
Gary
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