Laser not firing and head bouncing on gantry!

Machine: k40

Board: LaserBoard

Firmware: _Smoothie

Problem/ Question:
Hey, Just installed LaserBoard to my k40 and having a couple of issues.
Firstly, it’s like the end stop switches are not working. Both new mechanical type. Could be I’ve plugged them in wrong… as have two separate plugs, both 3 pin connectors(only uses 2 or them, signal/ground)
Secondly when I run a job from lightburn, the laser isn’t firing, laser fight led is flickering on board but no output from laser. Works fine when test button pressed on machine.
Any ideas?

And let me add, I have checked mechanical end stops and are both normally closed until pressed. I have also tried powering the board up with them completely disconnected and it still tries to home and hits the gantry.

First try this info from Starla.

Please provide pictures of your board, machine, and wiring. We’ll work on one thing at a time.

Tried the m119 command and it is not changing but when switches testing with multi meter, opening and shutting fine. And wiring is all checking out.

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I’ve got it firing now. Moved the ground to the ground pin near the laser fire pin. But still got homing issues.


The K40 almost always has homing sensors built in and carried over the ribbon cable. If this is the case, then by installing and plugging in additional switches, you are creating problems.

It was the optical sensors playing up which started this whole upgrade. X has been removed. Y is still on. If I unplug it near the sensor lightburn will not let me toggle left or right. It’s the Y sensor that’s stopped working originally. So how do I get it out of the equation so I can just use the mechanical one?

Well, they’re on the ribbon cable so you can’t just partially unplug the ribbon from the board.

You’d have to disconnect them on the other end of the ribbon, there’s a small pcb that breaks things out.

Use M119 to test with just the ribbon connected and moving the head to each end (ie: without your separate switches plugged into the board) to see which works and which doesn’t. You have to disconnect what doesn’t work first before you can add a replacement switch in its place.

Sorted! Unsoldered the old broken endstop and wired in the new mechanical one and she homes good!
Next problem is with the Lightburn camera, but I’ll start a new thread!