Shorted E0 endstop?



  • I had an NPN inductive sensor connected to my Duet3d Wifi and it was working flawlessly. One of my connector crimps failed and the wire made contact with something on the board around what I believe are the regulators. There were several small arcs but no magic smoke was released and I didn't smell or see any burnt components. I secured the wire and powered the Duet back on to find that my E0 endstop is constantly activated (i.e. Endstop hit remains at Yes). This is true even with the inductive sensor disconnected. The inductive sensor itself was also damaged as while it still will detect the proximity of metal the output of the sensor remains at .2 VDC with a 24VDC input. There appears to be no other problems with the Duet as I have changed the Z probe to a BLTouch and everything seems to be functioning again.

    What components are likely damaged on the Duet?


  • administrators

    How did you have the inductive sensor connected to the endstop input? In the wiki we recommend connecting a diode between the sensor output and the endstop input, to protect the Duet if the sensor ground connection breaks. If you didn't do that, then the supply voltage to the sensor (usually +12V or +24V) gets fed to the endstop input if the ground wire breaks. That will probably cause the endstop LED to fail, and may damage the filter capacitor and the main processor too.

    If the E1 endstop input is free, you can use that instead of the E0 endstop input for connecting a Z probe or filament monitor, but be sure to use the diode if you connect an NPN sensor to it.



  • There was a Schottky diode as connected as described in the documentation. I did switch over to using a different pin and re-crimped my connections. The printer is functioning again and I'm working on tweaks now. Thanks for responding.


  • administrators

    The Schottky diode should have protected the endstop input against over-voltage, so I am puzzled that the endstop input appears to have failed. I am also surprised that you had "several small arcs", which suggests to me a short between a power rail and ground.



  • The sensor I had was the model LJ12A3-4-Z/BX . It has three wires which are colored brown, blue, and black. The device was wired as such:

    brown: +24VDC
    blue: E0 STOP GND
    black: cathode of diode, anode to E0 STOP STP

    I can't remember which wire was responsible for the arcs but it was contacting the Duet board in the area between the +5 and +3.3 VDC LEDs and the E0 / E1 Heater headers. But like I said, the board appears to be working fine except for the E0 Stop.


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