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.

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Starting today i have a verry strange problem with my laser.
When the beem hit first mirror It take a rotund shape but with a empty middle, in the middle the beem seems to have no power, all the lens ar verry clean, What i must do?


Thank you for replay.
This tube have 200_250h is not so old, lens inside tube is clean… i have try with 50% and i have the same result and a verry bad one in final product.
Also i noticed beep coming from source When i engrave.


I bought K40 less then two weaks sgo.
Laser won cut. Alignment of the mirrors is good, focal point is also good. It worked well in the begining, I was able to cut 6 mm plywood with 40% power and now it wont cut 6 mm plywood even with 90% power.
I cleaned lens and mirrors, including laser tube outlet mirror and still haven’t solved the problem. I tried to readjust the height of the table, but it didnt help either.
At 10% power i hear funny sound from power supply. At bigger percentage of power it just burns material without cutting it.

Is there any solution for this? Maybe changing flyback could help?


Thank you very much on really fast answer.
There is sign ‘GBU 610’ on my bridge rectifier and I found out that it can go up to 1000V and 6A so it should be ok.
I will try to replace flyback and hope it fixes this problem.

One more thing about upgrading to a HY-T50 PSU. It wouldn’t cause a problem because my laser tube is 40w, and HY-T50 is for a 50w?


One more thing.
If I upgrade to T50 do I also need to change flyback or T50 has its own flyback included in itself?


Thank you very much.

I ordered T50, mA-meter and 24V, 4A extra PSU.

Next upgrade is probably AK-47 instead of laser tube. 😂

Thanks again.


You just red my mind. I was going to ask you how to upgrade to a T50 and 24V external PSU.


Great. I subscribed just now.

Thank you for your work.


T50 just came to my door and i dont know where to start. I am not good with electricity and I dont want to start without you.
Here is photo of my PSU:
Here is photo of my T50:

Extra 24V PSU is the same that you used in one of your guides.

You said that you are making a guide on how to upgrade to T50 and external PSU and I am stuck without it because anything i find on internet doesn’t seems to help.


Oh, I hope you get better soon.
I will try that.

Thank you for answering and stay healthy.


Hello, I recently bought a power supply from aliexpress, a laser tube from aliexpres connected everything and started checking the operation with the test button from the control panel. It seemed to be fine but after a while there were cracks as if sparks were jumping over, until at some point there was smoke from one controller on the nano board. I ordered a new nano m2 tile along with the control panel and plugged everything together and to my surprise I still heard a crackle every now and then. Moreover, when I changed the old power supply, the same thing happened. I finally insulated the metal parts on the tube and the crackling sound stopped but the laser power is weak. The beam does not reach the last lens and when I increase the power more, it only gets a small dot, on the 1st and 2nd lens the paper tape is nicely burned. And even after holding the test button for a longer time, the laser would stop. I don’t think I can see the plasma beam inside the tube but somehow burns the tape on the lenses

Last edited 1 month ago by Mateusz
Col Max

I have a K40 with digital control … The laser was used for about 5 hours in half a year … It didn’t go over 50% it was mainly used at 35% … Now I have a problem .. the laser has a very weak fire … and only works up to 22% if I walk over no fire … how do I know what my problem is … power supplies or tubes … or maybe something else..
I contacted the seller … but they do not respond ….

Col Max

ok … what do you suggest to improve that laser … and how to install the mA meter and which model do you suggest … if I change the power supply which model do you suggest and how to install it … I currently have 3 connectors …

Col Max

Ok. I’ll do it .. Thanks 👍

Woki Lopez

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?


Touohkomuk Lopez

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


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!!


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.


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.


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.

Ian Kerry

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.



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.


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.


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

Sophie Moore

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!


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?


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.


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