This article is just the findings and results we found on several PSU´s but we cannot yet explain why or how this happens.
Are you a electric engineer or have knowledge about the workings of the PSU and able to explain this phenomena in greater detail? comment below or contact me trough email – thanks!

The power supplys in our beloved K40 machines are poorly built, the power in them is barely enough for running the machine itself.

I have been following a lot of user lately which machines just stopped working or had other electrical problems and they all have one issue in common, the PSU.
Upgrading the PSU before use will stop the PSU problems if the tube goes bad or the rectifier burns to prevent damaging the flyback.
The upgrade is a couple of dollars worth, but can save you a lot of waiting and head ache later.

See this article how to find if it is your rectifier or flyback creating the problems – if your machine already have problems.

Mainly there is two reasons why the PSU fails and they all have a source in the same components.

1: Tube failure

When the tube fails the PSU tries to energize the tube and fails and either starts arcing internally or on the positive lead on the tube.
This often destroys or weakens the flyback transformer, it does not like the arcing and with time it will probably go bad.
To this date i have 13 reports of user experiencing arcing a while before the PSU died completely after a dead tube.

2: Rectifier or Flyback failure

The rectifier used in the power supplies are the wrong specs, the power created inside the machine is upwards to 2-3A and the rectifier is a 1A model.
When this goes out it often damages the flyback (high voltage transformer) and with time it will stop working properly.

Heat problems
Some PSU´s do not have a fan, some have one. The problem is if you run it for long the small chamber will heat up quickly and the PSU will try to cool itself with the heated air inside the chamber.
To sleep better, add a fan on the back pulling air out of the smaller chamber, or put your PSU to the wall breathing from outside the chamber. See this article about tilting your PSU.

Grounding issues
Make sure all grounds inside the machine is 100% good, remove the ground bolt in the back and remove paint so the ground has good connection into metal.
Remove the blue tape on the PSU and add a extra ground wire from the bolt holding the PSU to the case from the GND bolt in the back.
Double check the ground wires to the controller and panel too.

How to upgrade your power supply before use

The best idea is to change out the bridge rectifier the first thing you do. You need to solder it, very easy hole trough mount so a simple soldering iron will do the job.

Parts needed
RS507, 700V, 5A bridge rectifier – | Aliexpress | Ebay
(you can use 1000V, 6A or similar too, just keep it above 500v and 4A)

Step by step
1: Make sure the PSU is not connected to the wall outlet. If it is, remove the cable and wait 24h before you do anything. The caps can store a lot of power for hours.

2: Remove the cover from the PSU and unscrew the board from the bottom.
Take some pictures to remember what goes where if needed.

3: Turn the board upside down and de-solder the rectifier. Clean up the holes with some “solder wick” or similar. Solder the new one in place. Clean up the soldering job with some alcohol.

4: Mount everything back in reverse order.

In this picture the flyback is marked in a red circle, and the location of the bridge rectifier is located inside the green circle.

hvt flyback rectifier

Aliexpress advertising

10 thoughts on “How to upgrade your K40 power supply”

    1. Yes, we had a talk with a engineer in october last year, and since then they have upgraded the rectifiers in the PSU´s to 5-8A versions. No need to upgrade if you have a KBU610. They said the PSU´s was not actually made to drive the stepper motors and controller, only the controller and all extra load was eating PSU´s bigtime. A good upgrade for you later on is to grab a 24v, 4-5A PSU to let some load off from the laser PSU. You can find them cheap on ebay or similar.

  1. I ordered a 10A 24V power supply to drive accessories (pointers, lights, air, etc) which aren’t going to even come close to using 10 amps. Would it be a good idea to change things so the stepper motors draw from this new power supply instead of what came in my stock K40?

    1. Yes, the built in 24V is only supposed to run the controller board, not the stepper motors (said by the manufacturer of the PSU). Adding the motors to the internal PSU is something china manufacturers did to save money.

  2. Would love to get a 24v for the Controller board section. In the process of upgrading to a MINI GERBIL, and a larger area in the same case. Now the PS appear s to crapped out on me. Funny part ,is it works fine when impress the reset button on it, as long as it stays pressed that is. Any recommendations.

    1. Check all cables if you have a short somewhere, loose crimps or similar. It might be the rectifier too, a 50 cent part but it needs soldering.

  3. Greetings! Thanks again for a great article!
    Can you help me with something? We have a 150W CO2 cutter in the lab, the people before me stated that sometimes it started making squeaking noises from the PSU, months into use without any noise and then it started again but worse, I could see the arcing coming from the first flyback cable to the case with a loud noise and it stopped working and cutting completely. I put some high voltage liquid silicone around all the cables but apparently it wasn’t enough to stop that. We are thinking about changing the whole PSU but, could I just buy some 150W flybacks and replace the first with a new one? It would be a lot cheaper that way. Or is the real problem somewhere?, I’ll check for the kind of rectifier it has and replace it too, but will this be worth it, or should I just order a new PSU?

    Thanks in advance for any help!

    1. The flyback is fried (internal short on the copper windings), change it before it makes anything worse on your machine, open the PSU and check the flyback (or if its more than one) how they look and their connections, some has two cables and two bolts for power, others has three cables in and one out or more. Make sure you buy visually identical flybacks and with the same cable configuration and of course correct wattage. It doesnt matter if you buy bigger flybacks, i use a 80w in my 40w PSU, i need to watch out for over powering though to not burn the rest of the PSU components. But try to use identical power on the flybacks if you can find it.
      Check on the rectifier for any numbers, google it and buy a identical one or with higher amps, 2-5A higher doesnt hurt.

      Also, make sure all grounding in the machine is perfect. A badly grounded machine (or the components inside) can eat flybacks to breakfast. Make sure the PSU is grounded in the same spot as the wall outlet ground comes in, and controller board and all other electronics are grounded to the same point.
      Adding a EMI-filter can help too – but most 150w machines already have one. If it doesnt, grab one when you buy new flyback on aliexpress or amazon.

      In rare occasions arcing can happen when the tube is dead or dying, but the arcing is often happening on the positive pin on the laser tube – not inside the power connector in the PSU, so my bet is the flyback.

  4. My k40 will respond to files and follows the path but no laser firing. test switch on the power source will not make it fire. Rectifier is GBU610 so I should be good there. I suspect the tube or flyback transformer. The new flyback from Ebay is marked as ZY-08-40JS9. The transformer I have is marked as ZY-08-40JS9N. Will the flyback from:

    work on my unit despite not having the N at the end of the number? It looks the same wireing and all, just doesn’t have the N. The machine is only a couple days old,lol.

    Also could be the tube , but not sure. Will this tube work with my machine:

    Your site had mentioned I should just upgrade to the HY-T50 or was it HS-T50, either way I can find out, but if I upgrade to the T50 can I still use the 40w tube or do I need to still buy a new tube for the T50….assuming it will be a 50w tube?


    1. JS9 and JS9N is the same thing what i know, just make sure it has the same connections and same amount of cables.
      Rectifier you have is good!

      TongLi or YongLi tubes is the only thing i use myself, from my 40w machine to my 150w machines, they are great!

      HY-T50 is also my goto PSU, i have them in all of my machines. You can use a HY-T50, T60 or T80 with your machine, just make sure you never go past the mA for the tube you are using. Roughly 16mA max on a 40w tube. You will get a more stable beam on higher power with a T50 PSU.
      But, try with the flyback first to make sure it´s the PSU causing your problems.

      Another upgrade you might want to consider is a extra 24volt PSU to run the motors and controller board – it will smooth out everything. Grab a small one from Amazon or similar, 24V, 4A is enough and it´s very easy to install. (Stock PSU has 1A for both motors + controller, a bit low)
      We had a interview with a engineer last spring in a Facebook group a while back, he was one of the owners of the company who makes the blue 40w PSU´s and he said the PSU was never ever made to run the motors from the 24V – only the controller board. So that is a good upgrade!
      If you upgrade to a T50, you´ll need a external 24V psu anyway 🙂

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