BLtouch Pin not depoing anymore

  • Hello people,

    I ran into a strange issue and need some help:
    the BLtouch on my machine stoped wirking, after almost half a year of everything working fine. Just did a lager 14h pint jesterday and had no issues. This morning I wanted to start the next print but wasn't able to probe the bed...
    The BLtouch selftests fine when starting the Duet. But if I do a "home all" or even home one axis after the other, the pin of the BLtouch will not deploy and the hotend hits the bed, if I don't emergency stop it.
    Thats very strange because I didn't change anything from yesterday to today, same setup, same wireing...

    I'd love to hear your tips and suggestions cause i really nead the printer up and running again for work! Chears

  • Moderator

    I wonder if the heat from the 14h print was enough to deform something or make something stick?

    You can disassemble the BLTouch by removing the little set screw on the top of the housing, which allows you to slide the pin out for inspection and cleaning.

    but it's weird that the self test would work but not the actual probing.

    Try manually sending the M280 command to put it into self test mode and let it run for a while to see if the pin will get stuck or if it will move freely the whole time.

    Not a bad idea to check your wiring as well. 14h print is a lot of movement.

  • Hi,

    Well the self-test doesn't rely on the signal from the Duet so I would suspect that your problem has something to do with that signal.

    Some things to try/check:

    • Check that the wiring carrying that signal to the BLTouch is still good.

    • Try executing some of the BLTouch commands using M280.

    • Try using a different heater pin on the expansion connector, making the needed Duet configuration changes.


  • Thank you for the quick reply guys!
    After sending the M280 and switching pins, which both didn't work checking the signal wires did the trick! Turns out, that you were totaly right and one wire, due to my bad clamping and the long hours of printing, broke.

    Sadly still none of the probe related commands, like M280, do work. I have to admit that they never did work in the first place and everytime I had a problem with the probe I just restarted the machine, but today I realized that for situations like this they could actualy be of good use! So maybe you could help me with that as well.
    The probe is connected to the H7 pin on the Duet but in the config.g under z-probe it says H5. I found different info online on witch pin to use. I'm using a Duet wifi, not the last generation, with no additional board, no Z-endstop, just the probe. Which pin/pins do you guys use? And does the pin (H1...7) coincide with the H... in config.g under z-ptobe?

  • Hi,

    The numbering in the firmware and on the board itself can be confusing.

    For example there is support for three heaters and two extruders on the Duet itself.

    The heaters are numbered 0, 1, 2 while the extruders are numbered 0, 1.

    Heater 0 is the bed heater which means that heater 1, 2 match up with extruders 0, 1.

    For the expansion connector for the Duex5 the same issue continues.

    There is support for 5 heaters, 5 extruders and 5 PWM outputs.

    Continuing from where the Duet left off, the heaters are numbered 3, 4, 5, 6, 7 while the extruders are numbered 2, 3, 4, 5, 6.

    The PWM outputs on the Deux5 board are numbered 1, 2, 3, 4, 5 but they use the signal lines for heaters 3, 4, 5, 6, 7.

    To use a PWM output you first need to prevent the needed signal line from being used for a heater.

    The M307 command takes care of that: M307 H# A-1 C-1 D-1

    The # will be the heater number 3, 4, 5, 6, 7 which match up with PWM outputs 1, 2, 3, 4, 5.

    The M280 command will then control the BLTouch: M280 P# S###

    The # will be heater number 3, 4, 5, 6, 7 - the same number used in the M307 command.

    The ### is the "servo position" that the BLTouch responds to for a given operation.

    For example using 160 will clear an alarm condition in the BLTouch.


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