Does your K40 grind and causes noise when homing?

When you turn on your K40 laser machine it´s default setting is to home to top left corner and stop.
It happens that the machine starts to bang against the fence and it sounds like a grinding noise – it´s the belt jumping on the the drive pulley.
For some errors you can also see it moves to top but then suddenly starts to move to the right very slow. The cause is the end-stops for both situations.
If you have a external 24V power source for your controller board and stepper motors, make sure to power them on at the same time when starting the machine. Thanks to Eric noticing this in the comments!

The reason is actually pretty easy.

On both axis there is a optical end-stop with a metal tab, when it comes in to position the movement stops.
It´s also from this position the machine can calculate where the head is in the machine so it doesn’t run too far right or down.

How to fix it

Make sure the metal pieces are inside the optical end-stop in top left position.
If they are, check all cables and remove the optical end stops and inspect them. It happens that solderings are bad and cracks with time.

I suggest changing to mechanical end stops – article how to do this is being written right now.

Here is the Y-axis end stop circled with red.
k40 laser y axis end stop

Here is the X-axis end stop circled in red.
Located behind the laser head.
k40 laser x axis end stop

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I have this same problem – carriage moves to top left when I power on but doesn’t stop. The optical sensor bars are in the correct place but obstructing either of them makes no difference. Also the PC cannot see the laser so doesn’t load the driver when connected.


Thank you for this advice. How do I check this please? There are the 4-wire cables (red/green/yellow/black) that power the stepper motors and the thick ribbon cable The sensors each have 4 soldered pins – 2 on each side. I disconnected the motor power by unplugging both the 4-wire plugs, so it is quiet and not moving. I do not detect any voltage going to any of the 4 pins on either sensor. With the laser still on the pc still hasn’t detected it. Might the controller be caught in a loop? Thanks again for your help.


Here is the board. It is an m2 nano with ribbon connection for the Y axis.


See post below: it looks like the y-sensor has failed. Is it possible to buy a replacement y-sensor daughter board? Are there detailed instructions anywhere as to how to do this? I’m afraid I don’t understand much of the rest above – “extra connector?”, “regular limit switches?”, “disconnect the two optical switches?”, etc. Sorry but I am new to this so these terms don’t mean much. Are you suggesting I de-solder the sensors off the boards, or something else?


Sadly that didn’t work. I get 4.2V across the resistor and LED side, 0V across the sensor side – with and without a metal blade. I have ordered some TCST1030 sensors so – hopefully – can de-solder it off the board and replace the Y sensor.


TCST1030 successfully removed, PCB ok ready for replacement when it arrives.
Does anyone sell these whole boards with sensors, or where to look in general for K40 spares?

Last edited 4 months ago by hicksan

I think I may have found the cause of the problem. The Lihuiyu Nano M2 board has two sets of connectors various of its inputs and outputs. In particular the ribbon cable on its bottom left that carries the X and Y end-stop inputs and the X servo output has a separate X-servo output socket immediately next to it and then a Y-servo output socket and then the power input in a row along the bottom. On its right side – I now discover – another socket with X and Y end-stop inputs, with GND to either side and a 5th pin for 5V. This is immediately below the board’s serial number. On my board – now that I have removed it – I discover someone (previous owner) has linked together 4 of those pins, so the X and Y sensors are permanently pulled to GND by a line of solder. I am guessing this is why the Y sensor is always at 0V. The X-sensor works. I don’t see how, unless the solder joint is bad. What I can’t figure is why someone would do this? It doesn’t appear in any of the instructions and – on the face of it – seems just to sabotage the machine. Any thoughts?


Problem fixed. It wasn’t actually soldered. It was a drip of solder that had fallen into that socket – possibly when it was made or during some subsequent maintenance – and had become wedged in there and was shorting out all the pins. It pinged out with a fine screwdriver. All voltages now register correctly. Will reassemble and test. If nothing else a good learning exercise in how to understand how the machine works and what its various bits do!


To confirm: machine now reassembled, operational, homing correctly, initialized to the computer and responding properly. Now to start actual testing…


I removed the K40 y-stop daughter board from the carriage so I could test the voltage on the pins in the ribbon cables. My understanding is for the main 12-way ribbon pin 7 is GND and pin 10 should be 5V. This also should output to the smaller 6-way ribbon with pin 2 as 5V and pin 4 as GND (assuming I have numbered them correctly). I tested these pairs of pins and got between 4.17V and 4.24V across them – varying slightly by time but always the same for both pairs.


Across the resistor I get 1.81V and across the other two pins of the detector, closest to the 4-pin stepper plug, I get 0V in both directions, regardless of whether the detector is blocked with a card or not.


OK I think we have progress: I put a metal blade in each sensor manually and tested the voltage across the sensor pins, with 0V on the inside pin in each case. The x-sensor jumped from 0V to 4.8V each time the blade was inserted. The y-sensor remained at 0V.


I also checked the power feed to the controller board. As I understand it pin 2 is GND, pin 1 is 24V and pin 3 is 5V – these are all correctt. Pin 4 is referred to as LO and registers 4.6V. I don’t know what this is for.


First of all, thanks for all the information you share here, it’s been really useful.

I have an issue and I was hoping to get some info before I replace the controller. My machine homes correctly on the Y axis, but the X axis behaves erratically and never gets anywhere. If I manually move everything to the top left the movement stops, so the end-stops seem to be working.

I’ve also disconnected the motor and connected it directly to the controller instead of using the flat cable that carries both the X signal as well as the end-stop signals, and in that case the motor moves correctly.

Is this a common problem, or something completely random?

Thanks in advance!


Thanks for your answer! I’ll try to run direct cables to see what happens then, I’ve been suspecting that small board as well, but it seems so simple (just bridges and a single resistor) that it doesn’t seem possible for it to fail.

Thanks again!

mrs deborah wagstaff

mechanical end stop not working, need to know what to buy to replace on a K40 laser engrver

mrs deborah wagstaff

mine are a 6 pin, i got a 3 pin one but not sure how to install them.

mrs deborah wagstaff

they are the ones that came with the machine, i will try take some picks for you

mrs deborah wagstaff

sent them over for you, as best i can get photos of them


In my case, the homing didn’t work properly for a different reason. When I switched on the power, the laser head only moved a bit to the right and down, and quiet slowly. The reason turned out to be that I was switching on the external 24V power supply I added to the machine, which was powering the board and motors, but not the original 220V power supply for the rest of the machine. The 220V needs to be on before or at the same time as the 24V for homing to work.