K40 not engraving, power issue?

Hello all,

Looking for some help on this power issue I’ve been working on sparingly for the past few weeks.

Suddenly my k40 started giving out as far as power. I didn’t hear the normal hissing noise I’ve heard some speak of. I had to increase power to get things done until now there’s no more power.

At first I thought it was the laser tube, but I replaced it and still no power.

Then I aligned the mirrors and they are aligned. I get a strong test dot into the tape to the first and second mirrors…but it’s very weak at the mirror on the laser head. I have to hit the test switch up to 10x’s at 50% power for it to appear. When it does, it shows that it’s aligned.

I always use fresh distilled water with a little bleach, so that’s not an issue.

I’ve followed Don’s test pdf (which is genius) but get to “K” and then “R”.


The L signal is not wired correctly from the controller
• The controller is not configured properly for the port being used for PWM (L)
• The controllers PWM configuration is not correct
• The Laser module in the configuration is not enabled.
• The job is not sending anything to the controller
• The S value is 0 in the gcode.


I’m not sure which of these things I should check or that would apply to me because I haven’t made any modifications at all to the machine or the supply. I’ve used this machine pretty much problem free out of the box until recently.

When I do run a job and look hard, I can see a very, very light engraving very lightly scratched on the surface.

Suppose it’s possible I could’ve gotten a bad laser tube from ebay, but I’d still like to proceed in case that’s not the case. How would I test that anyways besides spending money on another…

Any help or ideas would be greatly appreciated

Please post a picture of your LPS.

Since you are getting some power but not full power I am assuming the problem is your LPS.
If you have done all the tests in the pdf that got you to “R” I assume the LPS is wired correctly and the external controls are working properly otherwise you would have found a problem before R.

Before we conclude you have a bad LPS lets check the final lens and mirror.

Common problems are

  • The last mirror is damaged
  • The lens is mis-positioned, cracked or dirty.
  • The beam is hitting the side of the lens tube

Post a picture of the beam (on a sticky) going into the head and at the correct focal distance on the bed.