K40 Laser cutter stopped firing . . .

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    Joel Brondos

    HELP! I’m “dead in the water.”

    The laser in my K40 stopped firing in the middle of a project. I had noticed that it wasn’t cutting very efficiently and had turned the current up — and the temps showing on my CW-3000 industrial chiller were up. It normally had been indicating temps between 19- and 20-degrees C,  but was up to 25-degrees.

    Now, after letting it sit overnight, I turn the main power off and on, click the laser switch off and on, and try the Test Switch, but the laser does not fire.

    The analog amp meter does not register ANY current when I click on the test fire switch. (I tried to keep the Amps to 15W max when cutting.)

    The stepper motors still seem to work fine, receiving and executing instructions from LightBurn software.

    What does this mean?

    Did I fry the laser tube . . . or blow something else? How can I tell?

    If I need a replacement laser tube, does anyone have any suggestions or warnings?

    I’d appreciate the help because I have so many projects I want to produce! 🙂


    Hmmmm. My temp has run for extended times at 26 degrees with no issues and i max my unit out at 16ma as a rule. That doesn’t mean the tube did not fail but I have run mine under those conditions since I had it and it is still running strong.

    There is some equipment on the internet to check flyback transformers (LOPT / FBT Testers). That may be one avenue.

    Here is one article on your issue. I’m sure there are others: https://k40laser.se/diy-how-to/troubleshooting-no-fire-issue/

    It does sound like, with what info I have, that it is likely the flyback transformer. Hope this helps.

    Joel Brondos

    Thanks a lot. I’d just as soon not have to buy a laser tube if I don’t need to.

    The site you suggested recommended the possibility of replacing the flyback . . . but I’m thinking I might just as well replace the entire power supply. Can you recommend a upgraded power supply for the K40?

    I still want to learn how to wire the 24V leads from somewhere on the power supply to the !2V 5A converter so I can power my LED lighting strips . . . 🙂

    And I may want to install a bottle turner someday which would be powered by that power supply . . .


    LightObject has a solid reputation and is in CA. They have all sorts of parts. You may contact them for recommendations.

    Check these links for more great info on the power supplies:

    There is info in these links that pertain to where to pull 24v from to connect your 24v to 12v converter.

    If you are considering running a motorized z and/or rotary attachment you will want to add a seperate 24v power supply. The stock K40 PSU will not reliably handle the current draw of added steppers and electronics. The 24-12 step down converter for the LEDs should be fine however

    Joel Brondos

    Very helpful leads, thanks.

    One last question based on a recommendation from your https://techbravo.net/k40/ site.

    You mention the inclusion of a Secondary 24VDC 6A LVPS (KNACRO 24V 6A 150W Isolation Switching Power Supply Module AC110V-220V to DC 24V AC-DC buck module by KNACRO). That is in addition to the power supply, right? Do you have a video which shows how to place that in the K40 case and how to wire it up?

    That’s all, thank you!


    It is an additional stand-alone power supply. I had to cut an acrylic base for it and mount it to the base using standoffs. Then I stuck it to the side of the chassis with 3M double sided tape. It has an input of 110vac line voltage that you can pull from one of the “sockets” in the back of the unit. and it outputs 24vdc. You may want to consider a 24v power supply that is encased as opposed to the raw board like I have.


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