Laser wire arcs to frame


I’ve recently bought a K40 laser and tested it today. Sadly when I tried to test the laser there is just some crackling noise and arcs from the red wire “small white box” from the picture.
I don’t see any water leaking into the tube so I assume the tube isn’t broken or anything.
I’m kind of out of ideas what it could be or what could solve it.
The ground wire is connected to the frame, the mA meter always stays on 0.
I also thought about isolating the white box and the rest with some silicone that came with the laser or the tube could be in some other way defect.
Does anyone have any solution?

By the way, I drew where the arc went out because I don’t want to run the PSU and damage it in the process.

Kind regards,


that white box is most likely a splice which was done poorly so you can probably fix this by doing a proper splice. High voltage likes to jump off any sharp points so if you google for how to splice laser tube wires you should see many ways which result in no ends of wires sticking out and probably instructions on how to apply the insulating coverings.

As for the tube Ground going to chassis ground is that really how it’s wired? I would think the wire would come from the end of the laser tube, to the mA meter then from the mA meter back to the L- or something like that on the Laser Power Supply(LPS). Or maybe you are just talking about the AC chassis ground people often mention needing to be cleaned up and made better instead of Laser tube ground going to chassis.

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K40 Intro at the top of every page here links into the #k40:intro section, including this article with resources on splicing correctly:


An unloaded LPS will arc from almost any weak point even a splice and sometimes directly from the anode.
The fact that you have 0 ma on your meter may mean that the cathode is not grounded or the tube is dead. Either will cause a violent arc from the anode side.

First, we need to verify that the cathode is grounded properly.
As @dougl mentioned the tube’s cathode should go to one side of the current meter and the other side of the meter should go to the L- on the laser power supply in the leftmost connector. DO NOT confuse that with L on the rightmost connector.

Note the L- on the leftmost connector

If that is wired correctly?

  • Does the plasma in the tube light when test firing?

Post a picture of your LPS showing the connectors.

A video of the tube firing/arching may also be helpful.

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Ok here’s a picture of my PSU and a video of the now suddenly nonexistent arcing, somehow it stooped.
Hope it’ll give you more information.

-First click (machine powering on)
-All the clicks after that (Pressing the laser test button)
-You can hear some sizzling sound I guess it comes from the PSU or the splice, I’m not sure.

Caution: It looks like the cover may be off of the LPS?
It’s not necessary to be inside the LPS at this time. This high voltage CAN KILL YOU so stay away from it!!!

I don’t see any plasma illuminated in the tube.
There should be a purplish line of plasma down the inside of the tube when it fires.
Is it there and I cannot see it??

Is there coolant in that tube? If so what is it?

What about the answer to this question below?

Try this:

Fire the laser with the test button down on the LPS. Does that fire the laser (plasma) and/or arc?

Please post a picture of your control panel.

From what I can see so far these things could be wrong:

  • Power control at the panel is not turned up or power control (IN) not working
  • An interlock or flow sensor is now open…
  • Cathode not wired properly
  • Tube is dead
  • LPS is dead
  • Both LPS and tube is dead
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Ok, one question at the time:

Is it there and I cannot see it??
There’s no illumination.

Is there coolant in that tube? If so what is it?
Yes and i use distilled water.

What about the answer to this question below?

I followed the cathode wire and it goes from the laser tube to the current meter and then into L- into the power supply.

I’m going to post a picture of my controll panel later that day.

Ok seems that there is no HV power to your laser, the next step it to do this:

There’s no Arc and no glow (plasma) in the laser tube.

Is this when you press the test button down on the supply?

Yes, I’ve tried both test buttons and nothing worked.

When power is on, at the LPS, is the red power LED next to the test button illuminated?

Yes, it is illuminated.

I think you might be replying to the wrong thread Don.

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@TwelveFoot thanks, that’s what I get for answering on my phone between casts… :flags:

Your LPS might be dead.

Do you have a DVM and can you use it???

A DVM? I have a digital multimeter.

I’ve got a replacement LPS from the seller, so I could replace it.

My question is now how can I know for certain that my laser tube isn’t broken?
So that the only problem is for sure the LPS.

DVM = Digital Volt Meter, a multimeter is fine.

There really isn’t a definitive way to test and isolate the tube itself.
I usually test all the parameters of the LPS and if they are good then the assumption is that it must be the tube.

Unfortunately both can be bad at the same time. A bad tube can cause the LPS to arc as it has no load and an arc can then kill the LPS.

Try this:

  • Adjust pot to max.
  • With your DVM (digital volt meter) :).
    • Measure the voltage on the LPS “IN” pin ** on the LPS to ground.
    • It should read about 5V.
    • If you adjust the pot up-down the voltage on IN should change.

**It should be the middle pin on the second connector to the left looking at the LPS.

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Can we all assume this is a new machine? When the tube on my machine crapped out it made a sizzling sound when I pressed the test button. And yeah from personal experience you DO NOT want to ever have the Hi volt output go through any part of you. Zapped my thumb one time and I never forgot it.