I’m using the OmTech 50W Laser with the Ruida Controller. My Laser stopped firing in the middle of a project. It continued to run through the motions, but without burning and now it does not fire at all. Any suggestions that might help would be appreciated.
Check your connectors - make sure you have not loose wires.
Sounds very much like a dead high voltage laser power supply.
However, as a quick test:
- With the machine power turned off, pull the connector from the controller out of the high voltage supply
- Turn the machine on and let it home normally
- Put some scrap under the laser head
- Push the
TESTbutton on the power supply
If the laser fires, then the supply is probably OK.
If it does not fire, then the power supply is dead.
The controller connector is on the right:
Caution: The TEST button is perilously close to the terminals carrying 120 VAC, so be careful poking your fingertip in there. 
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WARNING WARNING WARNING
Measuring that voltage with a multimeter will kill you stone cold dead
WARNING WARNING WARNING
The HV power supply output is around 15 kV, far in excess of the voltage rating for ordinary multimeters and probes, even if they’re of good quality.
Because you hold one probe in each hand, the fault current will pass directly through your chest, where it will instantly stop your heart. By the time anybody notices, it will be too late.
Be careful when you read AI-generated “answers” with that overly neat format, because they’re machine-generated garbage created from scraped Internet text, not actual experience.
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Don’t quote me on the source of this, but I think it was from one of the OMTech documents. Explains how to check the lps for 50 to 150W models.
I’d like to add, I think you’d be nuts to do this… however here it is.
ceramic-resistor-test-50W-150W-without-ceramic-cap.pdf.txt (446.4 KB)
I don’t agree to the level of danger of the parts in the machine. 
It would be nice to hear back from @BillBulloch about his progress.
I suppose they send you the resistor, because nowhere do they specify its resistance. If they expect 30-ish mA, it’s half a megohm = surprisingly high for a wire-wound ceramic resistor.
To a good approximation, room air breaks down at 1 kV/mm, so the supply will fire an arc across nearly an inch of open air from the hot side of the resistor to the machine frame, right through that 600 V tape. Foam insulation and corrugated cardboard not only don’t qualify as HV insulation, they make excellent kindling next to an arc.
My opinion of OMTech’s expertise just dropped 20 dB.
I believe it came from OMTech, so hold on to your feelings about them.
Well maybe, try this link.
If I recall, it a very low ohm resistor.. it’s essentially shorting out the hv.
The resistor on my machine to measure HV is 800mOhm. Allows a 50uA current at 30V.
I think it’s only testing the maximum current the lps can supply.
Pretty close to half a megohm:
600 kΩ = 30 V / 50 µA
But dragging a 15 kV supply down to 30 V seems brutal and certainly doesn’t test it under anything close to normal operating conditions.
My lps operates at about 12kV when running… Got something off, maybe it I was figuring a maximum of 30uA…
A max of 30 mA, which might be close to the usual maximum for those supplies, works with half a megohm at 12 kV:
400 kΩ = 12 kV / 30 mA
That’d be a more reasonable test at something like normal operating voltage and current.
I think of those big ceramic tubes as wire-wound, but maybe these days they’re all thin film. I strongly doubt the film + insulation is rated for operation at tens of kilovolts, but who knows?
