Please help me troubleshoot my dead K40!

A few weeks back my laser stopped firing half way through a project, I just assumed it was the laser tube as the one I had was the stock tube from 2014… Many hundreds of express delivery dollars later, I’ve installed the new tube and still nothing from the test fire :frowning:

A few things to note:

  • Machine still powers the fan and water pump
  • No squealing noises
  • Fuse is not blown
  • Nothing in the power supply looks shorted, no smell
  • The laser head moves to the home position when I turn on the laser cutter
  • All the lights come on and I get the little laser LED when I try a test fire but still no burn

Thoughts on what it could be? Am I just very unlucky and got a dud laser tube replacement?

Hi Linda,
A couple of things first.

  • Are you still running the stock controller?
  • Do you have the analog or digital panel?
  • Does the tube ionize (light up) when you press the test button?

Hey Ned, thanks for for the response!

It’s a stock controller with a digital panel and the tube does not light up when I press test.


  • Do you have any interlocks on your machine? (ie water flow, lid open)

  • Does the laser fire if you push the test button on the power supply?

There is a troubeshooting guide to help you in this blog post:

No interlocks… my unit is basically stock, power supply doesn’t even have the test button on it :see_no_evil:

Thanks Don, I did go through this flow chart guide earlier today and ended up at “S” - buy a new one or repair… :frowning_face:

Yeah, I feel your pain. Earlier this year I thought my tube had died but it ended up being the power supply. But with a new tube and power supply my laser is running better than new.

Oh it sucks big time… So should I upgrade my power supply to the Cloudray? My connections are different but I assume it will all work out the same.

Is this an old machine?
I have never seen a supply like that one!

Is that a black box in the center top? Is that a cover that comes off?

Looks like no matter what you get you will have to do some rewiring…are you up to that?

It’s circa 2014 from Aliexpress and I’ve wanted to hurl this machine off the balcony so many times lol

We’re a two engineer household so between the husband and I, we should be able to work it out :crossed_fingers:

ps. I have no idea what the black box is and the I tried to pull on it and it’s not a cover that comes off… I’ll send it your way eventually when I get myself sorted, it can be a new addition to your K40 LPS museum :upside_down_face:


OK stand by and I will make some recommendations.
Your location?

Bahrain… This is what I’m ready to get because I need express shipping:

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That will require rewiring such as:

  1. The ac from the back of your supply will have to be moved to the left green connector,

  2. The white 4 pin DC connector (rightmost) on yours will have to be cut off and rewired to the rightmost Green connector.

  3. The middle two white connectors will have to be cut off and rewired to the middle green connectors

Generally not to tough because the new supply has screw terminals and I can provide you a schematic if needed.

Here is my affiliate link :slight_smile: for the 40W:

If you are thinking about an upgrade to the K40 controller and power later you may consider that there is also a 50W: [but you have to also buy a DC supply]. Keep in mind that in the DC supply in the K40 is under powered if you do a controller upgrade.

Just found this one that is more of a direct replacement.
You would only have to move the AC power connections:

Thanks Don,

I saw this too! But they ship in 3-5 weeks.

I get questions all the time about LPS replacements.
Do you all think this is valuable??
See any errors ??

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I was thinking of replacing the HVT on my current power supply to see if it will work and then I’d have a spare LPS around which will be useful in the long run… I might pick your brain about it eventually when I get around to it :blush: Thanks for the spreadsheet!

There are two types of HVT you can tell when you take it apart and look at the links I sent.
Let me know how it goes.

The power supply arrived and we successful replaced it… Laser tube now fires! Thanks @donkjr and @Nedman for your input.

Now I just need to realign the mirrors with this nifty guide K40 Optical Alignment Guides Fun fun fun! :rofl: