71 thoughts on “How to troubleshoot a “no fire” issue”

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

    2. My machine will test fire and is aline but when actually running a program the tube doesn’t fire?

  2. 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. 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. 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?

  4. Hi,

    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?

    1. 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.

      1. Hello,
        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?

        1. 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.

          1. Hi all, if the laser fires bridging pin 5-6 – what is the issue? Which part do i have to replace?
            thanks from munich!

          2. Flow sensor is often the problem if installed on that spot. The potentiometer setting the power might be another issue. Cheap fixes.

          3. Hello, I am currently having the same problem, I can only fire from the test button on the power supply. On boot the display looks normal (“W” and “LOff”), then it switches to “NLid”.

            I have tried setting a magnet near the sensor but that doesn’t work either. I want to try to follow your directions – “Bridge P+ and GND, pin 5 and 6 …” but I am new to tinkering under the hood. I’ve googled and searched videos and I couldn’t find an answer. I don’t know what to do.

  5. 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?

    1. 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.

      1. 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.

        1. 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.

  6. 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.

  7. 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?

    1. 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 😉

    1. 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.

        1. 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.

      1. Hi HP, hi everyone, I’m Alex from Italy and since yesterday proud owner of not one but 2 k40 lasers :).

        I bought them used (well, 1 used 1 still in the shipping box, untouched) from a seller that works with wood but he prefers cutting wood by hand.

        I’m writing here because I cannot solve my problem: the power supply in both k40 was disconnected and the red wire cut, so i managed do reconnect everything but the laser doesn’t fire.

        Here is my step-by-step:

        1) water pump with tap water connected and on
        1.1) ground connected
        2) everything powered on
        3) laser head moves correctly using program
        4) laser doesn’t fire but, the strangest thing is that even the amperometer doesn’t power on: I have the older analog-amp version and the red, stop-button, digital power meter k40 but both doesn’t show life signs.

        Any idea?

        Thanks a lot

  8. 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?



    1. 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

  9. 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

  10. greeatings i have problem with power supply on k40 laser .
    when i try test i have some voltage on my cable on bobine but it isnt big and cant tube work.
    is problem with bobine or something else ???

      1. We replace tube, but same problem, i only cant test My bobine i have resistance between Black an yellow wire anything between red wire is it ok?

  11. Hey again! I have a quick (and probably simple) question when you have a minute. I’d like to upgrade to a 50 watt tube, so do you know if I also need to upgrade my power supply for this to work properly? Thanks for your time!

    1. You can upgrade the laser tube only, but you will not be able to use the full 50w without a PSU upgrade. It will work though.

      1. Thanks for your response! So I would get a little more power if I just upgraded the tube? Do you think it would be a marginal difference or worth it in your opinion? Definitely not looking to spend more money if there won’t be a decent difference.

        1. The 40w tubes are about 30-32w real watts. The 50´s are actually closer to 40-45w depending on brand and tube quality/health. You will see a small increase of power for sure. But be aware runnung the PSU on the edge of what it can do will cause stress and strange things. Not damaging the tube though, but the PSU might go up in smoke.

  12. New k40, digital type, laser looses ALL power during short use time. Unplug plug physical ac plug and power restored. Happens randomly, low or high power same thing. Any idears, it just completely dies and switching of then on nothing, need to remove the AC plug to restore.

    1. Sounds to me the PSU is overheating or has some kind of internal fault so it shuts down itself. Check for shorts or loose cables, and double check the ground wire.

  13. Great stuff here! I have been reading trying to diagnose an issue I have. I think my PSU has failed as I have no response from either test button and no glow or response of any kind from the tube. I am not a fan of arcing the HVT to see if I’m getting high voltage to the tube. Everything seems to pin out power wise, potentiometer read correct, and switches and fuse are all good. Can I safely assume the PSU has failed since I am getting no response from the tube?

    1. It´s 50-50%, it´s pretty rare with a PSU going totally dead, most of them get stuck at 2-3-4mA when the flyback burns. If your laser machine homes to 0x0, moving the steppers to zero position but cannot fire the tube i would test with the PSU first. But it´s hard to tell if its the tube or PSU actually. PSU is cheaper to swap though.

  14. No fire issue – SOLVED

    I’m posting this to help others with the same problem. I moved from a pc to a laptop and the laser cutter no longer fired. It would fire when the test button was pressed. I discovered that the USB outer metal shield needs grounding (yes, another grounding problem). A pc has it’s USB connectors grounded through the mains, a laptop (usually) doesn’t. If your k40 has this issue, try grounding the outside of the USB connector – this could be modified on the k40.

    1. Hi,

      was your experience like this:
      1. started a job from laptop
      2. laser was working and suddenly stops. Repetier shows the machine connected but can’t communicate, Only thing that helps was unplug and plug back USB cable. Even disconnect and connect on Repetier doesn’t help.
      I also have this behavior:
      1. power on the machine and connect USB to my laptop
      2. connect Repetier
      3. fire a couple of “Test” fires on laser panel
      4. Repetier “connected” but just stacking commands. If I just try to disconnect and connect, error shows up saying that it is unable to communicate. Only re-plugging USB cable helped again.


      1. As someone said in a earlier comment, if my tips in the article doesnt work – check your USB ground.

        1. Hi,

          shortly: connect GND from controller board to the casing of the engraver where also power plug “GROUNDING” is?


          1. …tried to connect GND from the controller board to the casing… No luck:( Still getting communication problems. I also noticed squealing sound from my LPS and sometimes even popping sound (after I release “Test” button. The mentioned sound is also present when “Test” button is pressed). As long as I can tell, the laser power is OK and ammeter shows increase and decrease of mA if I turn the knob. I also tried “full power” and the mA was around 23mA. I really don’t know what to try next and what might be wrong…

  15. Thanks for this guide. It helped me a lot.
    Problem started lke that: after 1 or 2 seconds of cutting laser went off. I powered off-on, then test shoot with the same result. Few times like that. I blamed PSU: broken fly-back or something like that. But after some time I figured out, that wobbling cables with pressed test fire starts laser.
    First thing I found was broken test button on PSU (I’ll have to change that). Then I found, that wires in ammeter’s connectors are oxidized and a little bit loose (I soldered them), then potentiometer connectors just slipped off (I soldered wires directly to pot). And finally I found, that crimp sleeves on PSU’s wires are loose (I also soldered wires’ endings and thrown away that useless junk).
    Wiring job in my K40 was shit.

    BTW. some PCs’ PSUs have quite high voltage: ca. 150V as ground potential when ungrounded. So never connect ungrounded PC to something, that is grounded, unless you want to fry some stuff…

  16. I have an issue with my Chinese 50w laser. Bought it brand new worked fine and while making a large order midway the laser working on a “job” it stopped firing but kept running the job. I was engraving at the time. Also when it stopped the red dot laser stopped working as well? I checked the board that goes to the red dot laser and noticed that one of the electronics that has the cool fins was hotter than normal and the red led light was not on anymore.

    I’ve ordered a new board but the waiting sucks. Any ideas to trouble shoot this issue?

    Test fire works, water sensor is good.
    Just doesn’t fire when job is running.

    Thank you,

  17. Hi, I have a 100w and mi laser is cutting the same no matter the power%, the controller is sending a correct 0-5v signal, and from the psu I dont know what happen but the output power is always the same. I can play only with speed and I cant engrave. What can be the problem?

    1. When this occurring it´s often a stuck power setting, so its sending 5V no matter what the setting is. If you can measure the value and its different for different power settings, i would look at double checking so all cables are where they should be. The PSU might burn and stuck to 100% power too, but its very very unlikely

  18. Hi.

    I have a Q switch Nd Yag laser tattoo removal machine.

    From some days now, it doesn´t work every time I press the button. Or if it does, it takes a long time to shoot.

    What coul it be?

    1. The YAGs works very different, it´s better to talk directly to the manufacturer about issues with these machines as they are built different. But a guess would be the button itself having issues or wiring or power supply. A YAG laser is often working or not, just half-way-working is very rare. Hope this helps some in your quest for solving your problems.

  19. HI!
    I was half sleep this morning and started cutting wo turning my cooler on….
    after 20 mins I went to check my job and the laser was not firing anymore…
    ammetter reads normal, but there is no fire…
    Is the tube gonne? or could it be the power supply?

    1. Have you followed all steps in the article? If you did, there is a 50-50 chance its either PSU or tube.
      You can do a test with the PSU and see if it fires, but its very very dangerous and i dont suggest it as a solution – See this video, but: Always keep one hand behind your back, push buttons with a wooden or plastic stick and dont lean against metal, wear shoes to be 100% safe: https://www.youtube.com/watch?v=EzpRGX23aFc
      If you get a spark from the PSU, it´s alive.

  20. Hello, I have recently brought a K40 laser cutter, it was all working perfectly, however it now isn’t doing what the design is telling it to, it just shoots a few shots in random places and then says it’s done? Any ideas?

    1. Do the test described in the article with removing the flow sensor if you have one and bridge the P+ and GND. Random spots tells me the signal to let the laser tube fire is intermittent.

  21. Hi, I have a 80 watt laser / Engraver and Chiller was cutting some 3 mm thick Acrylic at 80 Power and 22 speed cut about 150 pieces size 150 mm x 150 mm, all of a sudden the laser stopped firing but the x and Y axis was moving. Replaced identical new POWER SUPPLY. Laser fires from the Power supply TEST button, but from the panel PULSE doesn’t fire.
    Tried removing the two wire water flow sensor and shorting both terminals but no hope. Can some one help me as this is the first time happening to me. Tried contacting the company but no answer.
    Will be very thankful if you could help me sort this problem

    1. To me it sounds like the signal from the controller is not reaching the PSU, broken connector, cable or loose cable somewhere.
      To help in more detail, i need to know what type of power supply and controller you have in the machine.

  22. Dear Sir,

    Thank you so much for this valuable guide, I have a K40 laser machine, the other day my PSU and even the power socket burnt-out, I have replaced both, however when I tested the machine, it doesn’t fire when connected to the laptop, it will fire when it press the rest button on the PSU, if I bridge the water pump pins in the PSU than the machine will start firing as soon as I start it and will continue to fire until I switch it off, right now I am dead in the water and don’t now how to solve this issue, I will really appreciate your insight and suggestions.



    1. You probably have done something wrong with the potentiometer or digital panel. The IN, 5V are probably swapped. Try removing both of them with the P+ still bridged to gnd. If it stops firing, turn the IN and 5V cables around (move 5V to IN, and IN to 5V) and try again.

        1. Hi! I hope you can help me. I just bought a K40. It only fires with the TEST button. But when i set the design and the machine moves, it doesnt fire anymore. Only fires with the test button.
          Pls help me. Thank you

  23. Thank you Mr. Persson , it is working now, I swapped the cables now it is working perfectly. I really appreciate your advise and sharing your expertise with us. Thank you sir.



  24. Hello, I am at number 4 with my laser, i do not have a k40 but the controller is a M2 nano which is practically the same, my power supply is a 60 W one coz i have a 60w machine and tube, test button does not fire the tube and i have two indicators, WP which as far a s i know is water protection is always on and, LASER which is supposed to blink red when i press the TEST button, otherwise, the psu si working fine, fans running and all, (unrelated to the topic) is there a FB page or forum for this kinds of lasers? ) Thanks and best regards

    1. Make sure WP is grounded, if you have a flow sensor on it – remove it and just ground WP connector.
      Most forums and FB-pages on the topic knows these machines aswell, as they use pretty much the same components.

      The test-button located on the PSU should fire the tube, it bypasses everything and just put direct current to the laser tube. If that does not work you have a issue with the tube or the PSU.

  25. dear sir i have problem with laser tube fire , it is discontinuous fire , is the reason by tube damage , or maybe power-supply issue .. i hope you can help me to solve this issue .

    1. Follow the guide, if you still have problems it stops firing try with changing the potentiometer. You can test this by bridging IN and 5V on the power supply, it will fire 100% all the time. But if it works with this your potentiometer is bad.
      If you still have problems, i would try changing the flyback transformer, see this article: https://k40laser.se/diy-how-to/k40-laser-cutter-power-supply/

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