This guide is a work in progress and more resources will be added over time as part of continuous improvement. If you are unable to resolve your issue with any of the guides below, please email a support ticket to 

Before we get into the specific error messages and scenarios, you should know the following troubleshooting processes. These are quick and easy to do, and are relevant for many different issues. Familiarize yourself with these, they might come in handy!

Common Solutions

Power Cycle / Hard Reset

The classic “did you try turning it on and off?” solution. This may help eliminate some stubborn alarms and allow for recently-changed firmware settings to take effect.

  1. Disconnect on gSender, press the E-stop, then toggle OFF the power switch on the controller
  2. Wait for 5-10 seconds
  3. Then turn everything back on – toggle ON the power switch, press then rotate the E-stop, then reconnect on gSender

Clear Alarms

If you need to clear alarms that cannot be removed with any buttons in the visualizer, try the following.

  1. Click ‘Console’ in the bottom corner of gSender
  2. In the text box, type “$X”, ensure you are using capitals
  3. Click ‘Run’, this should clear any alarms

Restore Defaults

Restoring defaults means that you are reverting the controller’s firmware settings to their original factory values. This may be helpful in a large variety of scenarios, like if the machine is stuck in the homing cycle, if an axis is travelling inaccurately, and if limit switches are triggering too late.

  1. Click console in the bottom corner
  2. Type $RST=$
  3. Click ‘Run’

Generate Diagnostic File

If you are having issues and you are planning to contact customer support, it’s best to attach a diagnostic file, which contains information about your most recent cutting job. This can help our team figure out what went wrong.

  • This should be done right after first encountering your issue. Or if possible, try to recreate the issue. or after you recreated the issue.
  • Please try to recreate the issue, and as soon as it happens again create a ‘Diagnostic PDF‘ to send to us. If you can generate this shortly after the issue that’s ok too, but it won’t allow us to help you if you’re not connected to your machine or you generate it too long after you had the issue happen. Find this by clicking on the ‘Calibrate’ tool in gSender, then clicking the ‘Download Now!’ button in the bottom, right corner and saving it on your computer.

Controller or gSender


  • Pressing to ‘Zero’ axes isn’t working: Ensure $10 = 511 to enable “work coordinate offset”. We recommend the following is enabled in the $10 Status report options

  • Overriding speed, spindle, or laser doesn’t seem to work on shorter files: This is an outlying grblHAL issue which should only occur on shorter files. If you want to still override, you should still have the option to set the override before starting the job.
  • Issues with independent A-axis homing or hard limits: Earlier versions of SLB firmware might exhibit difficulties with this. In this case you’ll have to disable hard limits when doing 4-axis cutting, and if you want to do independent A-axis homing you’ll want to temporarily add it to $44 or 45, then run the independent homing cycle using the button in gSender or sending “$HA”, then remove the A-axis again from $44 or 45.
  • Incorrect motor behaviour (wrong direction, losing current, changing movement distances): Please report it to us then try to either power-cycle the board or reset it back to the Firmware defaults by sending the “$RST=$” command (soon you’ll also be able to use the “Restore Defaults” button). If this doesn’t work, check that the settings in the ‘Firmware’ tool match these as shown in this PDF:  altmill-default-settings-for-motors.pdf, as they affect motor direction, holding, steps/mm, speed, acceleration, and more.

Alarms and Errors

  • Alarm 3 or 10 take a couple of tries to unlock: In the newer versions of gSender (1.4.6 onward) this should be fixed where unlocking just takes some time
  • Alarm 10 on startup: You should be able to “Click to Unlock Machine” in gSender. If this doesn’t work, you can try to:
    • Turn on the board without the E-stop doing anything and the big LED should be Red as well as the small light next to “Halt” on the board which is near the big LED.
    • Rotate to unlock the E-stop, this should turn the smaller red “Halt” light off.
    • Click the Unlock button in gSender.
    • If your machine doesn’t change to ‘Idle’ (white status light), turn the board off and then on again and repeat this process until it goes through
  • Alarm 10 when E-stop is not pressed: the E-stop signal needs to be safe so it’s designed to be very sensitive. Check if you have any loose wires or have conductive material in contact with the underside circuitry of the E-stop unit, any of these cases could be causing it to trigger unexpectedly
  • Alarm 14 unexpectedly or during spindle setup: this would point to an error in how you’ve set up your spindle, either in the wiring, how you’ve set up the SLB EEPROM values, or how you’ve set up the PD values on your VFD. Double-check that everything is as it should be since if there’s a misalignment in any way then the controller won’t receive proper responses and send an Alarm 14 to protect the machine
  • Error 8 or 9 after hitting E-stop: The typical routine after hitting the E-stop will be to first ‘reset’ the board and then ‘unlock’ it, you’ll get either of these errors if a step in this process is missed. To reset the board, turn off the power then turn it back on.
  • Error 24 in gSender: Check that you are not loading up a regular g-code file while in Laser mode
  • Error 33 in gSender: Export your toolpath using the mm post-processor, instead of the inch post-processor.  Due to rounding, exporting toolpaths in inches can cause this error, because there is a higher chance there will be two lines with identical data in the g-code.
  • In the diagnostic file, “Spindle at speed timeout. Clear before continuing”: Spindle settings not correctly set, VFD not programmed correctly, or VFD not plugged into wall. Follow our resources for setting up the AltMill spindle here. If using a 3rd party spindle, please refer to our spindle information here. You may have to refer to your manufacturer for correct VFD programming and instructions. 

Check out this comprehensive list of common alarms and errors , with examples of instances where you might encounter them.

Preview of the alarms list, full list here

Mechanical Issues

Motor Dip Switch Position

If you’re experiencing incorrect movements on any of the axes, please ensure the dip switches on the backs of each motor are set to the following.


Other Issues

  • If there’s a problem when you “Import Settings” from an older Firmware version to a new one in gSender’s Firmware Tool, this is expected. Different versions of the SLB have different EEPROM outputs that won’t be compatible with each other, so for the duration of Beta testing you’ll just have to note down your changed settings manually and revert them manually on new Firmware versions
  • If you change a firmware setting and notice that it isn’t taking effect, check if the setting description mentions that you need to “hard reset” your board. Some settings need this, which just means you’ll need to turn your board off and back on again before the change takes effect.
  • If you hear the SLB ‘clicking’ when you change EEPROM settings, this is normal
    If you’re experiencing any issues with SLB ‘Disconnection’ while running your CNC, try switching from USB over to Ethernet.