Lightburn will not control power

I just bought a Monport K40 that was built in March of 2024 so it is a version 2 laser. Light burn will not control power. I have to manually control power. Any help would be greatly appreciated.

You have to tell us some more about what is going on with the machine.

Did it just break all of a sudden? What changed?

If it’s never been used with Lightburn, but works with some other grbl, that would be helpful.

How do you know it’s power and that Lightburn isn’t controlling it?

Do you have a voltmeter?


The machine is brand new and trying to set up. Watched all of the videos online and some says that you set the control knob to max and let Lightburn control the power from there and others say to set control knob @12ma using the ammeter and test fire button on machine. I have done both of these and when at max it stays at 0 with laser firing showing it is on at the ammeter. When set @12ma on the ammeter it goes to 25ma while firing burning up my material.

Here is my machine settings. do I need to change anything here to get light burn to properly control power?

Does it burn even when moving? Or is it able to turn the laser on and off?
The links on this page may be of use: Troubleshooting - LightBurn Documentation

As may this:

Some of your information is conflicting. This makes it more difficult to determine anything specific.

How can it lase with no current flow… This is some kind of misinterpretation of what’s happening as it can’t be – it cannot lase with 0 current flow.

How can you set this at 12mA, but it reads 25mA?

First I’d send a note to the vendor and advise them of the issue you’re having. In all likelihood we can help you diagnose or fix it, but if it’s a real problem your vendors support will be needed.

No need to run your machine at it’s limit of 12mA when testing, when you have an issue, use lower power settings.

I don’t suggest you exceed 50% power, protects everything in the machine, including the tube. When troubleshooting a problem NEVER run 100%, you’re just asking for it and it won’t help you diagnose what’s not working. Tube will use whatever current the lps will supply.

25mA on one of these tubes is destroying gasses, this is way too much current.

Can you post a photo of the control board and how it’s wired to the lps (laser power supply). A photo the lps is nice, as there are a couple different models.

Send a note to the vendor, it’s usually 24hour return times, so start it now. Post some photos…


The laser will turn on and off when running.

Been working with Monportlaser. They have not been much help. I have seen I am not only one with problem and nobody seems to have an answer on how to fix. I will get pictures sent tomorrow. But to go back what is said to be conflicting information no matter what I set ammeter at on machine when I send job through Lightburn even with a power setting of as low as 0.5 it goes either to the setting or over depending on whether I set using the test fire button on ammeter or if I set while Lightburn is trying to control it. I have been all over the place with s-value in both device and machine settings and nothing changes.

The problem with Monport is they won’t help anyone with any kind of technical help… how is the control board wired to the lps would really help us fix this… It’s not just Monport, but lately they seem to have a few issues.

I was hoping we could look at the photos and figure out some solution for your.

If we ignore the controller itself, we can look at the lps, since we know how the lps operates, we can check certain inputs.

An lps operation is relative simple and the pwm output should go to the lps IN terminal… If you could get a voltmeter, we can check this and make some determinations about where the failure maybe occurring…

We have to check voltages on the IN terminal of the lps to know anything.


My guess is that the test-fire button is set to Continuous, but Max Power was set to 50% on the Ruida at the time, and you get 12mA. Then a job commands it to fire at 100% and you get 25mA

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