Troubleshooting a “no fire” issue

Quick troubleshooting when the machine is not firing the laser any more.

To begin with, make sure all wires and connections are good in the machine and make sure all cables are where they should be.

1: Start the machine

Check the fuses in the back of the machine in the connector.

2: Do a test fire on the panel

If the machine fires, you dont have a problem :)
If the machine do not fire, go to 3.

3: Do a test fire on the test-button on the power supply

If the machine fires, you have a problem in the buttons, potentiometer or the cables.
If the machine do not fire, go to 4.

4: Load a file, or make a shape and try to engrave or cut it.

Only need to test for 5 seconds.
If the machine do not move or fire – you probably have a issue with the bridge rectifier (green in the picture below) and the internal fuse. It is a $1 replacement, soldering needed. Order a new one, 600V 6A is good for the rectifier.

If the machine moves, but no fire from the tube you probably have a issue with the flyback transformer (HVT). Marked red in the picture below.This is a $20-50 replacement depending on where you buy it and how quick you want it delivered. We sell them with EU delivery within 3-4 days here.
Or check out ebay or aliexpress to order a new one. Open your power supply and make sure your is visually identical to the listing on Ebay/aliexpress, there is different types.


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HP Persson

Digging up the strange ideas and convert them into useful tools and addons for the lasers.
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6 thoughts on “Troubleshooting a “no fire” issue

  1. Tom

    Dear Sir

    Just read your post and saw your picture.
    My new K40 laser will not test fire.
    The seller was very helpful and sent me a new laser tube but it still will not test fire.
    However there is a beam inside the laser tube when I pushed the test fire button.
    They believe the water sensor is not sensitive enough to trigger the laser.
    And they are sending me a new water sensor.

    Is that a possibility?

    Please advise
    Thank you

    1. HP Persson Post author

      You can remove the water sensor, bridge P+ and P- on the power supply to test it without the sensor.

  2. Rob

    Super-useful, thanks.
    I had a problem with the laser not firing. When I pressed the test button, I could see the ammeter register the current but there was no fire. I switched the whole machine off, then back on again (that one weird IT trick…lol) and it started working again. However, I find this very worrying. Is this possibly the flyback transformer?

    1. HP Persson Post author

      It might be a loose connection. Take off the lid on the PSU and inspect the 3-pin connector for the flyback, make sure its crimped properly and you have good contact on all three pins. Also check the machine if it has a water sensor, connected to P+ on the power supply, if these fail the firing can be intermittent. Also check the other cables on the PSU so the crimps are good and no damaged cables.

  3. Joel Brondos

    My K40 laser stopped firing in the middle of a project (using LIghtBurn and Cohesion3D Mini upgrade board). e.g. the stepper motor controllers seem to be working fine, communicating with the computer.

    When I click on the Test Fire button, NO CURRENT registers on the analog meter. Just before the laser firing failed, I noticed that the amperage seemed a bit erratic and did not increase or decrease smoothly as I turned the potentiometer.

    If this is likely to be the flyback, I’m thinking I might just as well replace the entire power supply and not just the flyback. Can you recommend any good power supply replacements — ones which could also feed an LED lighting strip and bottle rotation device if I ever should decide on one of those?

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