Dual End stops not functioning

Mostly Printed CNC - MPCNC Troubleshooting
1

Hello Everyone,
Done putting together my MPCNC PRIMO with an skr pro 1.2 board, which I got in November 2024. movements on all axis are fine but, I can’t get the end stops to work.

M119 always Displays
X_min: Open
X2_min: Open
Y_min: Open
Y2_min: Open
Z_min: TRIGGERED

I have tried the following but it still doesn’t change;

  • Disconnected all switches
  • Connected one at a time
  • Removed spade connectors and soldered wires to terminals (C and NC)

IMG_20250218_223718
IMG_20250218_2237181920×1440 95.5 KB

IMG_20250218_223904
IMG_20250218_2239041920×1440 215 KB

IMG_20250218_224259
IMG_20250218_2242591920×1440 115 KB

2

The limit switches are only querried when homing the machine, so, other than the LEDs changing on the board, the limit switches don’t do anything when just moving around. Do the LEDs chnge when you depress the levers? Are you homing when you run the tests?

There is a known issue with some SKR Pro boards where the LED lights on the board change but the homing does not stop. This issue is rare. To test, start homing and while looking at the LEDs for the endstops on the control board, then press a lever. If the LED changes state but the motor tied to the endstop does not stop running, then you have this issue. If so, let us know, and we can give you a list of workarounds.

3

Thanks for replying…

I did all the tests during homing.
The LEDs don’t change state (remains ON) and motors don’t stop moving.

4

Something is strange here. Can you provide a picture of the endstop block on the control board? I just want to make sure you have them wired correctly. In particular, you want to avoid the voltage pin in each plug:

image
image142×147 14.9 KB

Also, I assume you are using the bare limit switches and not the ones on the circuit boards.

Though this would not account for the behavior you describe, be aware the switches need to be wired normally closed.

Note if you have any wire with Dupont connectors on the ends, you and manually trigger an endstop as indicated by both the LED and an M119. You want to short/unshort the GND and the signal pin on any connector. This eliminates the wiring and the switches and specifically tests the control board.

5

Here are pictures of end stop block.
Yes, I am using bare limit switches.

Shorting and unshorting the GND and signal pin still gives same output as before.

IMG_20250224_053827
IMG_20250224_0538271920×1440 164 KB

IMG_20250224_053900
IMG_20250224_0539001920×1440 176 KB

IMG_20250224_053910
IMG_20250224_0539101920×1440 185 KB

6

If the LED are changing state when the wires are shorted, but the M119 stays the same, then this is a hardware issue with the SKR Pro board. This is a known potential problem with the SKR Pro.
Your choices are:

  • Replace the board

  • Disable the LEDs by removing them or cutting the traces going to them

  • Wire in a pullup resistor for each endstop.

Typically, a pullup resistor is directly soldered to the board, but it is possible to wire pigtails to plug into endstops that will accomplish the same thing.

If the LEDs are not changing state, then you have some other issue and we need to dig deeper. Typically, I’ve don’t see this issue happening to all the endstop connections, so I lean away from this being the SKR Pro hardware issue.

7

Or, you can make pigtails so you don’t have to mess with modifying your SKR board.

The quotes below are a re-paste of previous threads FYI.

MakerJimGuidance Counsellor

Dec 2024

There’s a chance you have an SKR pro with a known issue.

Here’s the thread where it was first identified:

Here’s a thread showing how this can be fixed by soldering on resistors:

Here’s a thread showing how this can be fixed by making a wiring pigtail adapter with integrated resistor:

EDIT: Fixed my links (I think)

1 Like