Z2 Motor is not registering end stop - on the odd occasion

I’m having an issue where the Z2, on homing doesn’t seem to register the Endstop and then falls and keeps trying. I have successfully cut previously the struts and some other bits, and even 5 minutes before having this issue going on to another cut…

I’m also running SKR Pro 1.2 with dual Endstop.

I noticed when I do the M119 the Z2 max is not actually triggered.
When I unplug the end stop it is always triggered.

This would usually mean my wiring may be faulty, however When I have Z2Max plugged in and click it I get the red LED coming on on the SKR board near the driver (as do the other end stops) - does this mean that the wiring is intact fine??? Or can the led not necessarily mean everything is working fully…

Any guidance on this would be awesome.

Thanks again guys!

I cannot say if this is your problem, but there is a known issue with some SKR pro boards. In fact the LED circuit is the source of the issue, and the LED can come on, but at the same time, the endstop not be registered by Marlin. The LEDs are pulling down the voltage so that the circuit no longer reads HIGH when the endstop is open. If this is your problem, your choices are:

  • Get a replacement SKR Pro board
  • Disconnect the endstop LEDs
  • Add a pullup resistor between the ‘s’ pin and the ‘+’ pin for each endstop (or at least the one that is failing).

Adding a 1K or 1.5K pullup resistor can be done non-destructively, or you can solder them in like the image where you started to post before. Disconnecting the LEDs is a destructive operation.

Here is the topic where the issue was first explored and solutions proposed. There are several other topics on the forum concerning this issue.

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Yes, the LED can seem to be “working normally” regardless if the MCU pin is getting the proper voltages for reliable operation. As Robert mentioned there’s a fundamental design flaw on the SKR Pro, which fortunately can be somewhat easily fixed by removing the endstop LEDs. You can add resistors instead, but IMHO that requires more skill vs LED removal.

Without getting into the electrical theories that explain why this happens… a new SKR Pro may end up behaving the same (or one that works at first may develop issues later on). So I’ll go as far as to say it is best practice to remove all endstop LEDs on new SKR Pro boards before operation. This will guarantee that the design flaw will not be an issue now or in the future.

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Cool thanks guys. I just tried homing again and it worked. And then failed. Letting it drain power for a while and booting it up again, it homes fine, and then not after that. So I’m thinking this is the fix I need.

I have some 1K resisters for another project. Would these be suitable or am I way off base? Matching the brown end to the brown in the other post?

And then secondly to go down the tear off the LEDs approach - do you mean literally pull off the tiny led that is between the plugs (therefore severing the connection?)

Thanks guys! :pray:

Those resistors will do the job. You don’t have to match the brown ends since direction does not matter with resistors. Also, you don’t have to solder them in to the bottom of the board in order to test if this fix is going to work. The resistor just needs to connect the S and the VCC pins somehow.

As for removing the LEDs, based on my limited experience with other projects, I’d be reluctant to rip them off because I might pull the trace off the board as well. I don’t have an SKR Pro to examine, but in other projects, I’ve used a rotary tool to cut the trace, or I’ve desoldered the component.

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OK that makes sense. Thanks for helping out a noob haha.

I might try crimp the resistor into the JST connector then and then give it a shot (making sure to connect the correct wires. :wink: Thanks!

Thanks a tonne Rob and Kev.

This specific solution did fix the issue for me and the machine is now running flawlessly (touch wood/sawdust).

I ended up decided to solder on the transistors on the back of the board as per the other thread being careful not to damage anything.

Not the prettiest solder in history, but would be my better work :stuck_out_tongue:

Thanks again for the help.