Laser loosing power

Machine: preenex k40

Board: c3d

Firmware: smoothie

Problem/ Question: I recently purchased the k40 laser and was using it without problems with k 40 whisperer. I decided to upgrade to the cd3 board lightburn software and a c3d rotary. Now when I am engraving the laser starts out fine but starts to lose power as it continues. I have spent days going though the forum and trying different things with no improvement. I reinstalled the original board and it works fine. Help I’m getting discouraged.

Did you provide those pictures? We need pictures to understand your setup!

Hi Scott,

Welcome to the forum!

Please provide pictures of your machine, control panel, board, other electrical components, and wiring to help us diagnose the issue.

I hope these help

Hi Scott,

Thanks for the photos. Can you trace these wires back to the LPSU (or other source) and let us know what terminals they are connected to?


Please elaborate on the types of tests you have done and results of those tests. Can you provide photos of an output example where the power fell off during usage?

Can you record a video of the behavior when you try to run a simple test, upload to YouTube, and provide a link here? It would help to see your laser tube while it is running as well. Below is the test I would like you to run:

  1. Type the following GCode in the LightBurn console to test. Ex: G1 X10 S0.8 F600

  2. Hit the Enter key to send.


  • G1 indicates this code is a cutting move.
  • X identifies the axis and the numerical value is the position coordinates to move to on that axis.
  • S is the power parameter. The example above is set to 80%, but you can try an S value of up to S1.0 (100%).
  • F is the feedrate per mm/min. The example below (F600) is 10 mm/s.
  1. The head should move while firing. The red status LED “Laser Fire Status” in the bottom left corner of the board should turn on (below the laser power and laser diode out screw terminals on the left side of the board).


Is the laser head moving while firing with the LED lighting up?

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