Nozzle crashes into print bed during calibration

Snapmaker 2.0
1

Hi,

I have a Snapmaker 2.0 A350T with the original single nozzle print head.
I’ve been printing with it without issues since january 2022.

I do a bed calibration every now and then (typically before each large print).
Haven’t had any issues, until today:

  • Upon the first calibration point, the print head moves down,
  • The proximity sensor light switches on,
  • But the print head just keeps on moving down,
  • So it just crashes into the print bed.

Nothing was changed mechanically, not even a bed swap or a toolhead swap as I have only ever used the machine for 3D printing until present.

What I’ve tried so far:

  • Update firmware,
  • Adjust the sensor height wrt. the nozzle,
  • Flip the print surface plate

It didn’t resolve the problem, which does not really come as a surprice as the sensor light has always been switching on correctly.

So I assume there might be some electrical connection fault either in the print head or the print cable.

Is there a way to read the level sensor status in Luban or through some G-code?

Or: is there a way to check the sensor ouput with a multimeter?
Based on this post it seems that the proximity sensor has no dedicated pin?

I’ve also been looking into swapping the print head cable, but I don’t seem to have a spare one. It seems not all cables are the same (not all have the same amount of pins).

Is the print head cable identical to those between the controller and the Y and Z cable splitters?

Any other suggestions?

Thank you,

2

I took the proximity sensor out, and the output connects to ground when metal is detected, which is consistent with “NPN normally open”.

So it seems the sensor is working.

So should I conclude that the print head PCB is broken?

3

The M119 G-code can be used through Luban’s command Console to check the status of the various switches, including the z-probe, and the filament runout sensor.

https://snapmaker.github.io/Documentation/gcode/M119

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4

@Mxbrnr Thanks, I had seen “M119 - Endstop States” in the list, but I had not realized that the proximity switch is also considered an ‘endstop’.

So I checked with M119 and that worked well, and then I reassembled the print head.

Strangely enough the calibration now automagically works again…

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