As you’ve tried, the M3 I needs to be put at the top of the finished g-code file. You can have it inserted automatically. In lightburn, you want Device Settings/GCode in the Start text box, enter M3 I.
Note that M3 I only works if you have your output set to Inline
Good morning! I’ve entered everything into Lightburn and created the g-code. The laser switched on correctly but unfortunately always at 100%. When the code is finished the laser stays at 100%? When I plug everything in and start up the board and laser the laser immediately switches to 100% and stays on, but if I briefly unplug the 2-pin supply cable to pin pc9 it stays off? By chance I hit a metal on the outside of the laser housing and the laser immediately switched to 100%? Do I have a grounding problem? What am I doing wrong? Thanks for your help Gerhard
First, I’d like to check your g-code file. Use the upload icon in the ribbon of tools and attach a copy of your Lightburn generate g-code file to a post. The icon looks like this:
Beyond that, we need to check what that pin is doing using a multimeter. As mentioned before, a couple of wires with Dupont connections make checking pins safer.
The multimeter will allow us to check if the issue is the SKR Pro pin or the issue is in the laser. If the issue is the pin, you will need to find another PWM pin and make new firmware.
pin Pc9 I measured 1.9V Thanks for your patience
; LightBurn 1.3.01
; Marlin device profile, current position
; Bounds: X0 Y0 to X15.56 Y20.06
;USER START SCRIPT
M3 I
;USER START SCRIPT
G21
G91
; Cut @ 3000 mm/min, 1% power
M8
M05
G0 X0 Y0.067 F0
; Layer C00
G1 X5.2 F3000 I S2.5
G1 Y19.995
G1 X-5.2
G1 Y-19.995
; Cut @ 3000 mm/min, 90% power
M8
M05
G0 X10.365 Y-0.067 F0
; Layer C01
G1 X5.2 F3000 I S229.5
G1 Y19.995
G1 X-5.2
G1 Y-19.995
M9
M05
; return to starting pos
G0 X-10.365 Y0 F0
Your 1.9V does not make sense. You are testing the pin without the laser connected?
You need to test the pin at various power levels. First, the pin should be near 0V when the SKR Pro is first booted. Then you need to run your laser program at various power levels. I suggest 1%, 33%, 66%, and 100%. If this is a 5V pin, you should see voltages around 0V, 1.65V, 3.3V, and 5V. If it turns out this is a 3.3V pin, then you will see voltages around 0V, 1.1V, 2.2V, and 3.3V.
Let me know.
So now I’ve probably done it right: 100% approx. 3.3 volts, 50% approx. 1.6 volts, 1% approx. 0.7 volts on the multimeter. I then put everything together and ran it through on the machine, including the laser, switching the laser on at the beginning and then off properly at the end. Unfortunately, the rectangles aren’t connected correctly? I’m already happy about this small step 
How or what do I need to change or configure so that the lines line up exactly when lasering? What else do I need to change so that it works in Marlin mode? I can switch to Marlin, but no cards or USB are recognized? Thank you.
I’m not sure about the lines not connecting. I’ve seen this behavior with M03/M05 for control, but the problem has always been solved by using inline commands. The g-code you posted uses inline commands.
It is possible there is a mechanical issue with your machine. Try the same rectangle at lower power and much slower speed and see if that changing anything.
There is a Lightburn page outlining similar issues and solutions, but I don’t think your issues match what they are describing. Here is the page just in case.
Thanks Robert for your great help! Same thing with slow movement! I tried filling with 3000 rpm 40%, if you enlarge the photo you can see the inaccuracy of the laser! The laser also makes a different noise when lasering than before the problem? Could this possibly be caused by the PWM frequency? I’ve read a lot on the internet and in forums but haven’t found a clear solution! I also tried something with the router with good success!! The mechanics should be fine! Perhaps you can find a solution with your great general knowledge 
Thanks Robert Regards Gerhard
I’ve now tried a G-code from a USB stick. When I plug it in, the screen immediately goes down and then back up again, but I can then execute the code. Not with the SD card! Is the machine angry with me?
There is clearly some sort of hardware issue. I don’t know if the issue is the laser module or the SKR Pro board, or in the case of the USB reboot, the USB stick. Before doing anything, consider testing with an alternate USB stick to make sure the problem is not the stick.
If the issue is not the stick, there might be a partial short somewhere, or one of the three voltage regulators might be flaky. Start by cleaning up the board. Vacuum any debris and make sure the bottom side of the board is not touching anything. Next make sure all the cables and the stepper drivers are seated. If the USB stick problem still occurs, unplug all the endstops and repeat the test.
As for the PWM, it is unlikely to be the source of your issue. You do want to make sure the S value is set correctly in Lightburn:
Thanks, it was the USB stick. I tried a new one and it worked! Are the four older ones I always used defective or what? I don’t have any end stops anyway! I have no idea why the laser makes a different noise and doesn’t engrave cleanly! Thanks for your valuable time!
Hello Robert! Dear thread, what should I try next? Should I buy a new board? Re-flash it? But what kind of firmware? Or buy a different controller? Can you please help me in any way? Thanks, Gerhard
One thing we need to understand is why inserting a USB stick makes the setup go wonky. It sounds like a grounding or power supply problem to me.
In fact the laser making a different noise hints at that as well.
Double check all your power/return connections are good, and if possible put a DMM on the 5V power supply rail and do some USB insert/removals of thee problem USB sticks. What to you measure when the reset happens?
Thanks Jim, the USB stick issue has been resolved. There was a problem. 
The new one worked! I’ll follow up on the laser noise issue again! Thanks, any advice is helpful!
Hello everyone! A few things have improved: the micro SD card now works on board in Marlin mode on the display, but unfortunately the current firmware no longer supports them! In touch mode, both work on the display. I wrote something in Lightburn and lasered it; the settings for both types of fill and lines were 3000 rpm at 40% power. It could be better, but it’s a small step forward.
Regards, GerhardI’ve thought a bit about your problem. When laser cutting and engraving, the CNC has to decelerate as it comes into corners, and then it has to accelerate back up after the turn. With inline commands, the firmware knows it is dealing with a laser and it moderates the laser output as it slows to make a corner turn, then turns the laser back up as it accelerates on its new course. It is possible there is something going wrong with the PWM signal to the laser or the way the laser is processing the PWM signal. If so, you might have:
There are a few things you can try:
First, you can try using M3/M5 commands and see if it makes a difference. Make this change in Lightburn:
Second, I know you did not want to mess with recompiling the firmware, but changing the PWM pin as I’ve outlined above will tell you if the issue is the PWM pin on the SKR Pro.
Third, you can wire the laser up without the companion board. With this wiring, you will have to ‘Y’ the ground wire so that it goes to both power and to a ground pin on the SKR Pro.
Forth, you might try alternate wiring between the companion board and the SKR Pro board.
Hello Robert and Jim! Thanks for your help! We (Michael and I) got the machine running again! Michael found an old Marlin firmware from March 2021 that I was using back then, and now everything’s working perfectly again! I use pin Pc9 for the laser. I’ll attach the firmware below; maybe someone with a similar problem can use it! Thanks for your valuable time. Regards, Gerhard
firmware.zip (113.4 KB)
I’m glad you got it fixed, though I’m puzzled by the fix. Lots of people use V1’s latest firmware with NEJE lasers without issues.
If you get a chance, post one of your laser projects to the forum.
Hi Robert, yes, that’s really amazing. I installed the old firmware and removed the M3 I from the start code in Lightburn and created the G-code in Inline, and everything worked as usual again 
. The good thing is that the SD cards on the display work perfectly again in Marlin mode; the micro SD cards on board were too fiddly anyway 
. Yes, I’ll post a few finished parts in the forum. Greetings from Austria
