Please help diagnose laser failure

Hi all, I recently posted about me changing the laser in my machine as I believe it’s dudd…just wanted to check with you guys before I do it.

When I press the ‘test fire’ button there is an arc sound (very faint) and there is visible light in the laser tube but nothing to even mark the tape on mirror 1. From this I am taking that power is reaching the tube but the tube is dead. Am I correct? Ill try upload a video

I know there’s an air bubble, rookie error

If there is no output from the mirror end of the laser?

This can be either a bad tube or bad LPS… or both.
Can you tell where the arc is coming from … I suspect the LPS?
Turn out the lights and in the dark see if you can detect an arc anywhere.

Warning: Be careful that you are not exposed to any laser beam or get to close to the HV.

Thanks for the reply - just had a thought, as I am super new to CO2 lasers I set the % power on the machine to 0.01 trying to be cautious. After looking on on forums a lot of people mention a similar noise on low power so I may try it at around 25% to see if that makes any difference.

There is no output at the mirror end no. Excuse my ignorance, what does LPS stand for?

Laser Power Supply (LPS).

The LPS will crackle at very low powers and will not output noticeable power.

Don’t be afraid to test fire the laser at various power levels 10, 25, 50, 75 %.
Just insure you use proper safety protection for your eyes and keep covers closed during the test.

I am guessing you have a digital panel and no laser current meter on the machine?
Post picture of your control panel pls.

LPS stands for Laser Power Supply.

And yes, im assuming you have a digital panel, 0.01 probably won’t produce anything.

Try small increases of 1, if you get to 10 on your display and still nothing then you’ve still got a problem

Sorry Don - didn’t see your reply.

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I really appreciate all of your help.

Pic attached. I’ll try again at higher powers tonight hopefully this is the issue.

Tested just and it it arced like a trooper to the case from the HV end of the laser. Thinking this could suggest broken tube or poor insulation?

What can I place over the connection temporary to see if it’s that?

So - I have just placed a long piece of 1/2” tube over the connection and tested.

I tested at 10% higher and the arc sound was the same as when I tested at 0.01% and no visible arc.

Still no mark on the tape on mirror 1. Any suggestions from here?

That has to be an insulation fault, regardless of what other problems exist. You could encase the entire line in silicone tube, but wherever it is arcing from there is definitely an insulation failure.

That was my thinking also. I have some RTV silicone arriving tomorrow so shall cover in fresh silicone and fresh tube and test again Monday. If that fails, I’ll replace the tube.

Thanks fro all of you help it’s very much appreciated.

I don’t think this is an insulation failure.

If there is reasonable insulation on the HV connection (silicon tube and silicon filler over the tubes anode) to the tube it should not arc to the case.

Typically this occurs because there is no load on the LPS because the tube is bad.

Note: repeated arcs to the case can damage the LPS.

How old and used is the tube. Have you checked for cracks?

I’m not sure how old it is if I’m honest, the guy I bought it off said it had been used ‘a couple of times’ but after getting it home it’s extremely evident it’s been well used. The mirrors were all burnt etc.

So it’s looking like the tube is the issue - I have everything I need here to replace it so I’ll just do that tomorrow. I decided to get a HV connector to join the cables, will make it easier to change the tube in the future too.


Let us know when it all back and working.

Soooo I went to install the laser tonight and it’s far too big. I’m not doing very well here, it’s 700mm and my current one is 600mm. Does that mean it’s 30w?

Typically length is related to power, and K40s typically are more like 30W… You can get an extension that sits off the right side to hold a longer tube. Might be a fortunate accident! :slight_smile:

Would I have to upgrade the power supply if I did? Sorry for all the questions