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Troubleshooting with your FluidNC K40 Shield

Written by Avataar120

Troubleshooting with your FluidNC K40 Shield

Please read this troubleshooting article before contacting me

Troubleshooting of FluidNC K40 shield errors/problems
Troubleshooting of FluidNC K40 shield errors/problems

Only applicable for FluidNC K40 shield
(>= v7 – black board)

Troubleshooting of the most common errors:

Homing fail. Could not find limit switch within search distance. Defined as 1.5 * max_travel on search and 5 * pulloff on locate phases.

This error is the most common one when you have purchased a 3 or 4 driver pack.
It is probably due to the fact that you don’t have a motorized bed and you haven’t disabled Z axis homing.
Enter the following two commands in the lightburn console:

G-code locked out during alarm or jog state.

This is the second extremely common error you will encounter.
When you power up the card or your laser cutter, the software does not know where the laser head is.
There is therefore a need to make a HOME each time you turn on your machine.
To do this, click on the HOME button in lightburn
You can also decide not to do HOME and remove this error to allow moves. I really don’t recommend it, but you can do it by entering the command $x in lightburn’s console

G-code motion target exceeds machine travel. Machine position safely retained. Alarm may be unlocked. (Right-click the ‘Devices’ button to reset the connection)
The last common error you will encounter is this one.
You are trying to send the head outside the working area
I set it by default with 5mm < X < 315mm and 5mm < Y < 215mm
The error can occur on both sides of the interval
If you have not done HOME and you are trying to move, you will often get this error because the machine will try to go to X= your request and Y=0 (which is outside the area) or Y=your request and X=0 (which is outside the area)
Make a HOME with the lightburn button before making your moves to avoid having this error

Homing fail. Cycle failed to clear limit switch when pulling off. Try increasing pull-off setting or check wiring.

You shouldn’t get this error unless you have a problem with your pull-off limits.
Check limit switches

Unclosed shapes (circles, rectangles, …)
First check that your Lightburn settings are correct.
The cutting parameters of each layer must be defined with the “Constant Power mode” option activated

If it’s still not working, it is possible that the default settings I propose are not suitable for some K40 power supplies.
If you notice shapes that are not closed (missing 1-2mm no more), please update the firmware AND the configuration file of your shield (see this article)
If the problem persists, you can enter the following lines in the Lightburn console:

Filling/engraving issues

If you have filling issues or image engraving issues, like in this photo where the circle is supposed to be 100% filled, enter the commands:
$cd =config.yaml

Squeaky motors
The motors can squeak because the K40 motors are not of very good quality and the drivers must be adjusted as accurately as possible to avoid passing too much current through the motors
I do not advise you to touch it because you risk breaking down your machine, but if it’s too unbearable, you can adjust the drivers a little by turning clockwise the screw of the noisy axis (it’s very light … a hair … no more)

Motors skipping steps – random distances
If the power sent by the motor drivers is not sufficient, they can miss steps, especially during strong accelerations / high speeds.
If this happens to you, contact me for asking me for an opinion before modifying driver settings.
(In general, it is enough to turn the screw of the driver concerned a little (a hair, not more) counter-clockwise)

Crashes – Guru meditation error
If you get messages like:
Guru Meditation Error: Core 1 panic’ed (Cache disabled but cached memory region accessed).

Core 1 register DUMP:
PC: 0x4010c430 PS: 0x00060035 A0: 0x80089B50 A1: 0x3ffbf19c
A2: 0x3ffb4778 A3: 0x00000000 A4: 0x3ffcbc74 A5: 0x3ffbdbe8. A9 : 0x00000002
A10 : 0x0000001a A11 : 0x00000000 A12 : 0x3ffb1c70 A13 : 0x3ffb1c30
A14 : 0x3ffc043c A15 : 0x3ffb2f20 SAR : 0x00000000 EXCCAUSE: 0x00000007
EXCVADDR: 0x00000000 LBEG : 0x4008ad64 LEND : 0x4008ad7a LCOUNT : 0x00000000

Try disabling WIFI or connecting your shield to your wifi network (link)
To disable wifi, enter the following command in the Lightburn console:

You can activate it again with this command :

Soft Limit errors
If you get SOFT LIMIT errors like:
[MSG:INFO: Soft limit on X target:400.000 Limits:-1.000..316.000], it means

  • either you have requested a movement outside the authorized working area. I set it from 0 to 300mm for the X axis and from 0 to 200mm for the Y axis,
  • either you don’t HOME each time you start your machine for the first time

You can either perform a HOME before each first use of your machine, or you can also disable the soft limits… I don’t recommend doing it at all but here are the commands to send to do it:


No response when entering a command in the Lightburn console
Check that you have activated the DTR option in the Lightburn settings (Menu Edit / Device Settings) as requested in my tutorial on installing Lightburn

If you have other problems:

Please make sure you have the latest firmware & configuration : link

If these common errors / problems do not solve your problem, please contact me via discord (Avataar120#7932).

Attach to your message:
The copy of your shield’s configuration: $CD command in the lightburn console
The copy of the shield startup message: $SS command in the lightburn console
What you are trying to do as explicitly as possible (especially the installation tutorial step)
What you expect as a result
What you get as a result
The copy of the error message in the lightburn console

Thanks !

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