Laser output not working through Cohesion board, works on self test

My K40 was working very, very well in all respects up to the point where I shut it down yesterday. Starting it up again today, I find no output to the laser tube via the Cohesion board. The stock K40 power supply has a test button on it and when I press it, I get laser output, telling me the power supply and the tube are OKAY. I can jog the head on both axes and “draw a test square” around the bed, but there is no laser output. I’ve changed colors, moved artwork around, even re-installed the smoothieware. It all seems to point to something on the Cohesion board not outputting the signal to the laser power supply. All wiring is intact. The manual test switch on the panel doesn’t trigger the laser either. I went further and used a jumper to short out the “laser switch” terminals and also the “test switch” terminals. THAT DID NOT WORK, which leads me to believe it is the power supply INPUT that is at fault. What do you think?

I had a similar problem ages ago. Try the fix in this article to see if it resolves the problem : -

You can see how I wired it up - the blue and brown wiring from the board to the power supply.
Take heed of the warning about incorrectly wiring the board though otherwise you could fry the board!

I received my brand new Laserboard, and experienced the very symptoms you describe… I trawled the forums looking for similar situations…
X/Y works fine, Laser indicators all light up, Air works, etc…etc… and I looked into the ‘re wiring’ you described.
Then I focused on that last component AFTER the LED, but before the laser. That little 4 pin IC which looks like an opto-isolator… and sure enough, 3 of the 4 legs were not attached.
Little time with a soldering iron and … yippeee. making small controlled fires… errr… uhmm… i mean.
Laser is now operational.
Hope this helps.

I’m surprised this would happen with a cohesion board, which I consider very well made. On a K40 laser, yeah, I can see issues like that becuase I found 1/2 dozen myself poorly made K40s. My K40 would fire with test button on power supply but not with switch input. I could have troubleshot but since I was upgrading, I just bought a 50W power supply for future consideration. I’ll fix the K40 supply for a spare.

I agree, the C3D board is very well assembled, this one little component just didn’t want to cooperate and settle down into it solder bed. I am thankful that it at least kept one leg attached, had it gotten free from the board, I would not have 1. found it, 2. known it’s orientation, and 3…been in any kind of mood to attempt emergency surgery.