Troubleshooting a “no fire” issue

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.
Read up on the grounding-article here

1: Start the machine

Does the machine home to top left position? if it does – go to #2
If it does not move – check fuses in the back of the machine, and inside the PSU – do this without power cable connected.

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.
You might have a water flow sensor connected, remove it and bridge the two connectors it was connected to with a small cable.
Test fire again.
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.


Share this post

Comments (25)

  • Tom Reply

    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

    8 January, 2018 at 20:37
    • HP Persson Reply

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

      21 January, 2018 at 10:42
  • Rob Reply

    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?

    21 January, 2018 at 09:25
    • HP Persson Reply

      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.

      21 January, 2018 at 10:41
  • Joel Brondos Reply

    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?

    19 February, 2018 at 16:23
  • Gabe Reply


    I can only fire from the test button on the power supply (step 3). Any tips on fixing the issues with the buttons, or wiring?

    7 April, 2018 at 00:37
    • HP Persson Reply

      Make sure the cables from your panel in the lid are connected properly. Also, a test to make is to remove any cables on P+ and P- on the PSU and bridge P+ to P-(gnd) with a small cable to see if the laser is firing after this. A common problem is a flow switch not working which will disable the firing. (test fire on PSU bypasses this protection). This is probably your problem.

      7 April, 2018 at 00:51
      • Tyler Reply

        I am also having a no fire issue, it will fire from the “TEXT” button
        I removed the water brake wires and still no fire, only fire is from the test button
        any other suggesting?

        17 July, 2018 at 04:08
        • HP Persson Reply

          Bridge P+ and GND, pin 5 and 6 if you count from left. Put a piece of cable between them pins and it should fire from the software too.

          17 July, 2018 at 21:50
  • Fran Reply

    Hi. I have an issue with my K40. When firing at low power settings, it works well (ampmeter reads 3-4 mA and laser fires), but when I increase the power, laser stops firing, and ampmeter shows a very low readout (1-2mA).
    Could it be the flyback is damaged?

    11 April, 2018 at 15:28
    • HP Persson Reply

      Do a test, on your power supply you have connections marked IN, 5V next to each other. Remove the cables on these two and put in a cable between them, then do a test-fire again. It might be your potentiometer (power knob) beeing faulty, this test shows if it is – you will see very high power so do not run it for long like this. Take a photo before removing cables, or mark them so you can put them back.

      11 April, 2018 at 17:40
      • Fran Reply

        My machine is the one with digital panel, so no power knob. (also I have a cohesion3D mini board).
        I’ll make the test, and see if it fires at full power.

        11 April, 2018 at 20:42
      • Fran Reply

        Hi. I made a video showing some test. Please take a look and tell me what you think. Thanks.

        12 April, 2018 at 14:12
        • HP Persson Reply

          Hard to tell, it might be the tube. Have you tried bridging 5V and IN on the PSU? At the same time, quick loss of power can also be the flyback – but it´s often arcing on high power.

          13 April, 2018 at 10:26
  • Pablo Verity Reply

    Also, my K40 won’t fire reliably much below 20%, but it does have some hours on it. For testing purposes, try at least that.

    17 April, 2018 at 12:06
  • Jonathan Reply

    Have you ever heard of or experienced the actual laser tube being the cause of a power supply failure? I recently bought a new k40 machine and the tube stopped firing in the middle of a job. The supplier sent me a new tube and it didn’t work, so I’m now waiting on a new power supply for that machine. I ended up trying the first laser tube in my other k40 machine and it worked great for about a week and then stopped firing in the middle of a job, just like it did for the other machine. Any ideas?

    11 June, 2018 at 22:46
    • HP Persson Reply

      Never heard of it, but it´s a common problem when the flyback dies in the PSU´s. Too warm in the psu compartment, tap water or bad coolant, too hot coolant can do that to the flyback. When you get the new PSU, make sure to upgrade it. Article is on this website 😉

      11 June, 2018 at 22:56
  • bob Reply

    i heve this problem can you help me please
    see the link

    22 September, 2018 at 12:37
    • HP Persson Reply

      Check all wires to and from the tube so they are seated properly and no damages. Also check the ground bolt, i have a article about it. If that doesnt help, its either the psu or the tube broken.

      22 September, 2018 at 12:53
      • bob Reply

        Hello my friend
        they sent me a new power supply but is not easy to install
        can you please help me

        8 October, 2018 at 14:40
        • HP Persson Reply

          Visit the facebook-group and search för HY-T50 to find schematics how to connect it. Link to the group can be found in the bottom of this page.

          8 October, 2018 at 14:43
  • Juan Reply

    Hi, i upgrade my K40 Láser PSU, and the Newone has diferent pin layout. Anyways i figure ir out how to connect all. BUT 🙂 … Láser dont work when i try to cut/engrave.
    If i press the PSU test switch it works perfect. If i press the láser panel test button it works perfect. Any Clue?



    12 November, 2018 at 23:54
    • HP Persson Reply

      Make sure you have WP pin to ground, or connected to a flow sensor. It can also be marked as P, WP, Water protect and similar. Also important with the L cable from the controller board to the PSU, often marked L, LO or TH

      13 November, 2018 at 08:56
  • Juan Reply

    Hi HP, thanks for the Fast Reply. I found the problem. Im using 2’PSU 1(Laser PSU) 2 (Switching PSU) all MUST share Ground. That was the problem in case someone has the same issue. Thanks for all the info you Give here every day !!

    Best Regards

    13 November, 2018 at 13:03

Leave a Reply

Your email address will not be published. Required fields are marked *


5% OFF

Be the first to know about our exclusive items, New catalogs and special promotions.

Currently high flow of orders which makes our handling a bit slower - we are training new employees at the moment! Dismiss