OMTech K40+ Smoothieboard Power seems backwards

I recently purchased the OMTech 40W and their K40+ control board for LightBurn. Here is my problem. If I want to engrave with LightBurn set to 20%, I have to set the power on the machine itself to at least 60%. What’s even more strange, if I want to cut with LightBurn set to 40%, the laser will not cut until I turn the power down to 30% on the machine itself. Any suggestions?

I don’t know about OMTech control board. Does it wire directly to the lps?

The output of most pwm is a positive percentage. If you are wired into the L input, it’s inverted… The power seems like it’s inverted, but you have to check how it’s wired…

I assume you replaced the original board ?


I replaced the original board with OMTech’s LightBurn compatible board. It does not give any instructions or pin-out information, that shows how to wire the board to the LPS.

You need to help us, without anything on how it’s wired … I can’t really help you any further…

Maybe someone else had knowledge about this…


Unfortunately, OMTech doesn’t have any diagrams of their LightBurn compatible board. If I can determine which pins are IN & L, I would be set.

There are a couple of different power supplies for these lasers…

Can you take a photo of the lps?

Do you have a voltmeter?

Has this ever worked properly?


Firstly I have no knowledge of the board you’ve referenced at all other than looking up the board online. So take anything I say with a grain of salt. From what I can tell the board is a Smoothieware board and has an onboard SD card. If so that card should have a config.txt file that can be edited. Assuming your power levels are reversed or inverted you should be able to modify the config.txt file to correct that if that be the case by adding a “!” after the pin number in that file. If the OMTech config.txt file is similar to the Cohesion3d files it will be on a line like this. “laser_module_pin 2.5”. If I needed to invert that pin I would change it to this “laser_module_pin 2.5!”. If you choose to look into this make a backup of the file somewhere you can restore from should things go poorly. Your best source of information to resolve the problem is OMTech though.

ETA: I just went to their website and found this manual which should have been included with the board. You might review to make sure you installed the board correctly.

I confirmed the K40+ control board is installed correctly. So, I decided to go back to basics to and clean all mirrors and lenses. It was when I started the beam alignment, that I noticed the tube was operating in TEM01. I’m getting a split beam on mirror #1. SMH…

Sorry to hear that… Time to for a new one…

Let us know what happens…


UPDATE: I received a new tube and the issue has been resolved. Thanks everyone!

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.