Close to figuring out the issue but need help

So long story short my laser stopped firing mid-job and I originally thought it was the power supply. The laser would not fire pressing Pulse, and the red light would not come on. After doing some research I learned that if I disconnect the large green plug from the power supply, hit the TEST button, and the laser fires, then the power supply is good. So then I inspected the wiring near my tube and discovered this:

After seeing that I had a bad connection, I changed out the connections and my red light turned on once more…for a few seconds. Then it turned off and never turned on again. I traced the black wire that had a faulty connection back to the mA meter. Would a faulty meter cause the laser to not fire properly or am I chasing the wrong issue?

Please advise.

That smudge suggests the failed HV connector (*) probably killed the power supply by shorting the high voltage output to the metal frame.

The power supply output runs around 25 kV, enough to start an arc across an inch of dry air, and the resulting overcurrent torches the supply’s output circuitry.

In this case, the meter wasn’t involved, but any break anywhere in the HV wiring, including the “ground” return wire passing through the analog meter, will produce a similar result.

(*) That’s not an HV connector. This is an HV connector:

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Thank you for the quick reply. So I swapped power supplies which comes with the connector you showed, but am having the same issue. Is there something else you would suggest I replace and/or inspect?

Your photo looks like it’s the cathode wire, which is the ‘ground’ side of things and you don’t see this happening. Probably why it’s not an hv connector.

I would hazard a guess that there is a loss of ground from that arc point towards your meter and to ground. This could happen with an open mA meter, but is easy to check.

mA meters are virtually straight through, so you need to limit current to it to check it. A resistor and small variable supply is perfect. However, I’ve use my digital multimeter on low ohms to check it. Do it quick while watching the mA meter, usually that’s enough current to move it. If it moves, it’s probably OK.

It makes little sense that this would arc here. The only explanation seems unlikely, but I’ve been delusional before…

If the voltage gets high enough with an open cathode it could conduct causing this. The counter to this is it probably takes a much higher voltage than the lps could produce to accomplish this.

Normally this occurs on the anode end when a tube fails and the hv goes pretty high…

This is the anode end of the tube. The bigger red wire is the high voltage ‘anode’ and the smaller black wire it the ‘return’ or to the mA meter then ground.

An easy way to check the meter is to jump the meter out of circuit with a jumper and test fire it. If that wire is connected to ground, there is no way it will/could arc…

Make sense?

Good luck


Thank you. 90% of it made sense to me. I’ll see if I can give that a try this evening after work. Just in case, I ordered a replacement meter since they’re just a few bucks on Amazon, but it will take a week to get here. If I cannot figure out how to test it in the meantime, my guess is that I can temporarily bypass this meter altogether right?

That is a way to test it. I think something isn’t grounded at that end somewhere and it could be the meter.

There should be no operational difference.

Good luck, let us know what happens…

Stay away from both of the hv leads when testing, it can ‘reach out and touch you’… Where it arced it’s unlikely you will be in there but just an fyi.


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Understood. Thank you. Is the other wire that comes from the meter and goes into the power supply the ground?

It looks very much as though the crimp wasn’t tight enough on that bullet connector and the wire pulled out, which shouldn’t be possible with a good crimp. On the other paw, I recently got a batch of crimp terminals made from the finest butter-soft copper-like substance, so maybe the crimp just sort of relaxed over time.

If the tube’s low-side return wire opens, the power supply will force enough voltage to fire the tube and strike an arc at the disconnected wire, which means the normally “grounded” wire will be at a few kV above whatever grounded metal is nearby. With a bit of luck, the voltage drop through the tube + arc may be high enough to keep the fault current low enough to not kill the supply.

If the meter’s internal wire burned out, it might have left an air gap inside the meter longer than the one at that connector, in which case the next pulse from the power supply would arc past the connector insulation to the metal frame.

Proceed carefully!

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Getting closer and closer. I replaced the mA meter and the black wire terminals by the tube. I believe I have an intermittent connection because when the red pointer light is on, it flashes on and off randomly and I hear what sounds like a relay click coming either from the Ruida controller or the piece behind my green laser button:

Please let me know why you suggest/recommend. Thank you.

Fix the intermittent …


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Is it possible to have clicking coming from the RUIDA controller or would it more likely be from that relay in the photo? There too close to each other to tell where the sound is coming from.

Ruida is solid state so co clicking unless its arcing.

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What green laser button?


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This button in the right.

That green button is a normally open switch, so it should not be making any sound at all.

Your descriptions seem very much an intermittent wiring fault, perhaps a broken wire shorting to ground. If the HV supply and tube aren’t solidly connected and properly grounded, you may be hearing an arc.

Find it and fix it, because whatever the cause might be, a short circuit (or an arc!) is not doing your equipment the least bit of good!

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I know the yellow component I posted a pic of earlier that sits behind the green switch definitely clicks. I just hope it’s not arcing happening with the controller at this point. On a more positive note, I think I found a loose ground. I tightened that up and plan on running some tests tomorrow. I truly appreciate all the help.

So now the laser seems to stay on HOWEVER if I press PULSE and move the head with the controller arrows at the same time, it blows the fuse in the back. It’s the only way that I can get it to blow the fuse. I’m sure people will just say “well don’t do that and it’ll be fine” but I would like to know what’s causing it. I don’t see any arcing. I wonder if it’s something visible at night time.

UPDATE: if I try to cut, the machine blows a fuse. No more audible clicking/arcing though. I can engrave as long as I keep the machine under 5mA

I was told to check the voltage on the two white wires circled in the photo and that the transformer with the red arrows may be bad. I can’t find find a part number on the transformer to replace it though. Does anyone know what that might be?

I don’t even know what that round thing is… :thinking:

Without knowing what the ‘two white’ wires are…

Did you measure them?


Apparently it’s a transformer converting my machine from 220 to 110. I’ll be measuring the white wires this evening.