This guide will help you identify and solve most problems with your laser machine not firing the laser beam.

Make sure your K40 turns on and homes to zero position.
If it doesn´t, check the fuse in the rear power connector before continuing.

Step 1

Turn on your machine.
Open the lid on your panel and push the test-button located on your power supply

This is good, your PSU and laser tube is healthy and working.

Go to Step 2

The most common problem when the machine is firing with low power, and mA-meter showing 2-5mA no matter what power setting is set – the flyback transformer is often the issue.
This part is avalible at ebay, aliexpress or in our store. Make sure to visually identify your type of rectifier before ordering one.

If you want to step your game up a bit – upgrading to a HY-T50 is a good upgrade, this PSU does not have the issues the K40 power supply has.
Avalible on amazon, ebay and aliexpress.

You have a issue with your PSU or laser tube.
The flyback transformer might be the issue but there is no guarantee it will solve your problems.
I suggest upgrading to a HY-T50 instead of buying a new K40 power supply (not sold by us).

This guide cannot identify exactly your problem any closer than this.

Things to try:
– Make sure you have grounded the machine properly – see this article
– Check all internal connections for breaks, bad crimps or loose cables.

Step 2

Turn on your machine.
Push the test-button on your panel, and/or through the software you are using with your machine.

Great – you don´t have a issue with your machine 😉

You probably have a issue with the protect function of the power supply.

Try this:
– Put a bridge or small cable between P+ and P-(gnd) and test the machine again. If it fires it´s whatever security solution connected to these pins that are your problem.
Often a flow sensor is connected, inspect it and sometimes it can be adjusted to allow for less flow/pressure.

Check this picture for pinouts

If you have upgraded your controller:
Make sure the power supply, any extra 24V power supply and the controller is grounded to the same point, often the ground bolt in the back of the machine.
You can also put a small cable between the laser PSU ground to the screw terminal ground on the Cohesion3D controller.
Same solution with other controllers, make sure they are grounded on the same spot.

26 thoughts on “How to troubleshoot no fire issue”

  1. Thanks for this guide. When I test fire the laser both with the test button and the power supply test button there is a clicking but no laser. Do I need to replace both the tube and the power supply. Which would you suggest to do first? Seems a waste, is there anybody who recycles these?

    1. Without doing a high voltage test its a chance. The tubes doesn´t die quickly, they fade away in 9 of 10 faults with them. But the PSU often dies over a second. I would go with a PSU to start with, or only the flyback transformer.

      1. Thanks, I will do this. You mention elsewhere on this site the Hy t50 PSU..can this be used with the k40 or will it be ‘overpowered’? I have the digital readout – yet to install a mAmmeter.

        1. Hy-T50 will work good on the K40. Just keep a eye on the mA-meter not to over power the tube. I have changed to T50´s in all my machines, one even have a T80.

          1. Ok, I have just ordered one, will let you know if it fixes my machine. Thanks

  2. Hi Ive been searching high and low and you have identified the problem!
    I bridged my p+ and GND on the PSU (type 2) and my laser fired at last.

    Now – i dont have a flow controller anywhere on the machine that I can find, so how do i go about fixing it? Or should I install one?

    I have nothing in my k+k- port (PSU type2) and my P+ GND (PSU type 2) plugs into P+ and p- on control board.
    I have a JK-K3020

    please help, ive been trying for days!

    1. If you do not have a flow sensor, you can bridge P+ and GND, just make sure you have water flow before using the machine. If you have the digital panel some connectors will be missing, it test-fires through another pin so it´s ok with missing cables on K+/K-

  3. Hi HP, I’m posting here because a friend of mine asked me to fix a faulty K40 laser. Basically when I light up the machine the laser head starts aligning bottom-right instead of up-left and the motherboard seems to work fine: the laser doesn’t fire at all even when I press the test button, no fire, no noise, nothing, even the amperometer seems dead. I’m working on, as my friend says, a new power supply but I did a mess so I’m trying to figure out what is wrong.

    Is there a way to test if the flyback transformer is working? Which voltage should go to the flyback? Thank you a lot, you are the only one who can help me 🙂

    Alex from Italy.

    1. Homing down and right is probably the end stop no connected or broken, when it doesnt get a signal it goes the opposite direction. Check the end-stops – both of them as they are going wrong direction. The flyback should not be measured at all – it´s 12-16000 volts in that one and you need special meters to measure it properly without dying 🙂 There is a redneck-test, putting the positive lead aprox. 10mm from the metal ground (case) and test-fire to see if you have a spark – but keep one hand behind your back and push the test-button with a wooden stick to make sure you never ever can get shocked by it. I always suggest bying a new flyback instead of doing a test like that, they are like 20-25 USD + shipping from china. You can use this pic to see what´s going where on the power supply ->

      1. Perfect, I’ll give a try soon. Thanks for your support and compliments for the site 🙂

  4. HP,

    Had a problem with my k40 laser tube arcing after rastering something, went to the cut command and lost laser power quickly over 2 seconds. Lots of arcing. After investigation, I noticed the laser was arcing inside the case. I had previously thought it was arcing outside of the tube because of a small black spot on the backside of the laser tube, but after putting silicon on it, I retried and seen it was arcing from the anode. I added silicon there and now no fire. I had a lot of condensation and everyone acted like that was a big no-no, but its 85+ degrees out and 90% humidity, 15-20C makes my tube condensate like crazy. any advice on my condensation problem? also, would you guess that the laser tube is just bad instead of being the HVT? laser still has movement, just no power.

    1. If it´s arcing the PSU is good, you might kill the HVT with arcing though. I have 120mm computer fans added on each side of my laser tube, one pulling and one pushing on all my machines, it cools down the tube slightly from the radiated heat and moves the dew point further away. Some machines has a hole for longer tubes, put the fan there. You can try with one pushing air in to begin with.

  5. Hi HP Persson,
    Was wondering if you could advise me.
    I have just exchanged and inserted a cohesion3d laserboard, upgrading from a Nano. All the lights on the board are doing what they are supposed to do.
    When I use lightburn it goes through all the motions of cutting/engraving, but no laser! When I press the test button on the laser it works fine and the ammeter registers, its just when I run the program.
    Truly baffled!
    Any help would be greatly appreciated Thanks.

    1. Make sure you have a common ground between the C3D board and the the ground point of your laser machine. And make sure the laser PSU (power supply) and the 24V power supply is also grounded at the same point.

      If you you a small 24V “brick type” PSU for the controller, take a cable and put between C3D ground pin (Negative -) and Laser PSU GND pin (Negative -) (any of them) or directly to the ground bolt in the rear of the machine.
      See this picture as reference. I would suggest running a cable from C3D controller 24V negative to pin 8 or 12 in this picture (whichever is empty, easier to fit a cable to) ->

      I have this solution in all of my machines, no matter what controller it uses.
      – 24V PSU is grounded in the controller board – and one cable going back to the ground bolt in the chassis.
      – LaserPSU is grounded to the ground bolt in the chassis
      – All extra PSU´s (for lights, fans etc) is grounded to the ground bolt in the rear.
      They all share the same GND no matter if they are feeded from the same inlet-cable or have separate cables.

  6. Hi HP
    My machine is 1 month old. The first 10 days was the only point. 2 points after 10 days. I bought a new tube and used it successfully. There is no single point problem for 10 days. then again point 2 comes back. Like two commas. What do you think could be breaking the shot? No sleep at night for a long time. I’m tired but I found this blog. I hope you can help. Sorry for my bad english.

    1. Split beam is common problem. There is different causes for it.
      When you get 2 points, check with a paper right on the laser tube if the 2 points are created out of the tube – or any of the mirrors.

      Problem 1: If you run the machine on very low power the beam can be unstable and split in 2.
      Problem 2: Hitting the edge on a mirror or a bad quality mirror can cause 2 or more points/shadows. Put a piece of paper in front of each mirror to see where the double dot is created.
      Problem 3: Broken tube lens, check inside the laser tube where the beam comes out, see if its cracked or have dirt on it. Clean it.

  7. Hi HP Persson!
    I just discovered your page and I am excited! Much information and detailed articles. Thank you!

    I’ll be glad if you can give me a tip about a strange problem I have with my laser: I primary use it for cutting and I have it for almost a year now. Everything was good till last week. It works for 4-5 minutes and then while in the middle of the job the laser won’t fire. However the amperometer is working and turning ON and OFF depending on the job. Now the strange part: If I move the potentiometer all the way to 100% (while the machine working) leave it for 10-15 seconds there and returning it to 20% (where it usually works) the laser starts firing again and the machine works fine! However it will work for 3-5 minutes and then again the same problem. I am not sure what is causing it… I use distilled water, the mirrors are aligned. Any ideas?

    Thank you in advance!!

    1. I would bet you have a problem with the flow sensor, if you dont have one make sure you have a bridge between P+ and GND (P-). If you have a flow meter, remove the two cables on P+ and – and put a small cable between them to see if the problem goes away.
      If the problem goes away, your flow sensor is bad – some types can be adjusted by turning something inside them to make them more sensitive for the water pressure. You can also upgrade the pump to a better one to have higher pressure/flow.

      See this article for a picture of the pinouts:

      1. Hi! Thank you for your detailed reply. My machine doesn’t have a flow sensor. I tried a bridge as you suggested but nothing happened. Still the same problem. As far as I can tell the cables from that positions lead to the laser switch that works. Also the problem just got weirder. The laser fires at all power percentages but the beam only hits the target when I run the power at 20-30% (that’s 5 to10mA). I thought that there was an arch inside the laser tube when firing but I can’t see anything. Thankfully I have another K40 laser and I can do my work. I have a love/hate relationship with those machines :p . Any comments are appreciated.

        1. Try this
          Put a bridge between 5V and IN on the PSU.

          Try running it now. But be aware – this bridge will cause the laser tube to fire 100% all the time so keep hands away.
          If this works, your potentiometer is bad. Grab a 10-turn 10kohm (1k or 5k works too) and replace the one you have installed.

          If it only works half way or just on different power settings it might be the potentiometer. It might be a bad tube or flyback too but i dont think so.
          The beam inside the tube you can see is just the plasma, it should dance a bit around the negative ring connected to negative cable.

          1. OK I tried the bridge but no luck. I can see the amperometer reach around 20mA and the plasma inside the tube but no laser beam exits the tube 🙁 Also I tried changing the potentiometer to a 10-turn 10kohm but again the same thing. The laser beam stops exiting the tube at around 0 to 4mA. Then as I turn the power up the beam exits and the machine works at around 5mA to 8.5mA and upon 8.5 and above no beam exits the tube but I can the see the plasma grow brighter as I increase the power. Concerning the plasma it wiggles a little around the negative ring especially on higher powers. Any other suggestions are really appreciated.

          2. Take a look inside your laser tube, from the end where the beam exits. If the lens i cracked or dirty.
            But, the strange power tells me you have a PSU issue if you checked the bridging and are sure you dont hit the edge anywhere, i would go for a Flyback transformer as a first piece to swap out.

  8. Hi, so I just got my k40 and set everything up and went to test fire and got nothing.

    On a hunch I put a piece of tape over my fixed mirror in the back and the laser tube did indeed fire and mark the tape. So does this mean that the mirrors are just terribly out of alignment? Like so out of alignment that the bean is not reaching the laser head?

    Also ever time I turn on the machine the gantry moves towards the front of the machine, eventually it will try to keep going and make a grinding noise. Could this be one of the end stops?


    1. Hunt the beam. Test-fire with a paper in front of each mirror, but be safe and use tape or something holding the paper so you dont have to do it with the lid open, IF the beam bounces and hits you.
      Most common issue for this is hitting a edge or inside the laser head due to bad alignment.

      If it grinds, like skipping on the belts you have a problem with the end-stops. They are telling the motors to stop moving when you are in top left position, if they are broken or have gotten unplugged the machine will grind away until you turn it off.
      Follow the cables from the end-stops back to the controller, look if they are connected properly. If they are, make sure the small metal tabs are not bent and fits inside the black little part on the end-stop.

      1. Ok, thank you so much. I really hope I can get this going without spending more money…

        1. Send a email to if you need step-by-step assistance with checking the end-stops. The help is free and does not cost you anything.
          We provide free help to find out problems and issues others have to write better articles.

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