Turned on K40 laser the other day... got a problem not firing during run cycle

Four plus years old with light usage a few hundred hours. I heavily modified this K40 when I bought it new. C3D mini, Pelter cooling, temp controller, new 10turn Pot, ect, ect and never had any problems until now. I thought the old PS (type 2) was failing so…I replaced it… the 10K Pot, checked wiring & cooling system (this K40 came without a sensor I have a visual). It’s not a digital display unit. Fires through control panel switch and on the PS. Laser tube test shows strong clean manual beam with pot set at 2.5 volts, mirrors and lens clean and good alignment. Everything seems great accept it will not fire in any of my old or new programs. I can post pictures (as soon as I figure out how).

Is this the Steve Clark with the peltier system back in the day (2018) ??
If so welcome.

Picture of LPS connectors?
How are you driving the LPS from the controller? The L pin?
If so;
Disconnect the L pin, add a jumper wire and touch the L pin to the ground pin and see if the laser fires

Hi Don…Thanks…Yes, I’m the that guy. I’ll get a picture of the LPS connectors up. My cell is not posting pic out right now so I’ll have to get the DSLR out . Not sure how to post the pic yet. I guessing it’s a drag and drop to the screen or hitting the upload icon. Last night I was thinking about it and I may have, when replacing the LPS, inadvertently switched the 2 pin P+ Grn and K- K+ plugs when putting it back together. I’ve got to go out and check that. What would happen if I did that? Any idea?

Those are typically switched contacts so it would do no damage. Of course, depending on what you have connected they won’t operate the same/correctly.
When the power to the machine is on. Does the LED down on the LPS illuminate?

Yes, Everything ‘seems’ normal however no signal to fire within the program.

This LPS has a fan (the old one didn’t) and it’s running.

Either of those, plus also you can cut/copy the picture and paste it in.

“2 pin P+ Grn and K- K+ plugs” Hummm? I did switch the plugs? The K- K+ is to “Laser enable” and P+ Grn is “Test sw”. I’ll switch them back and let you know the results.

OK it’s fixed! I think either my Pot had gone bad or the LPS was failing. Anyway, when I replaced the LPS I accidentally plugged P+ Grn in the left 2 pin receiver and K-K+ in the right. On my setup it will not fire in the program in that case. Thanks for the help Don and Michael. Don, thanks for your hand drawn schematic on your “Don’s Laser Things: K40” site.


OK I’m back the Laser is acting up again power flow is fading during the cut . So…I think it is time to buy a tube. So what thoughts if any do you all have??

Links here: