Hello
The pin of X-,X+,Y-,Y+,Z-,Z+ on the RAMPS 1.6 board are no voltage or low voltage(0.28V), that cause the endstop to fail. When the motors are back to origin, the motor moves a small distance in the positive direction instead of moving in the negative direction. And the LCD12864 display "Endstop X/Y/Z". Does it mean that the main control chip is broken? The fact is the same, after I replaced the new atmega2560 board, the endstop was normal. If it's not a atmega2560 chip problem, which part should I replace? Thank you.

Endstops are often 2 pins... signal and gnd signal is pulled high when not grounded (you have to enable ENDSTOPPULLUPS)

moving the wrong direction a little then stopping... means the end stop is already triggered.

Use M119 manually trigger X enstop, send M119 note what it says. release X endstop Send a new M119 if it changes but is inverted, you just need to invert the Axis X_MIN_ENDSTOP_INVERTING

If it doesn't change. Its something else.

Also there is an entire section dedicated to ramps, you might want to use that section as this has nothing to do with printing. [reprap.org]

Edited 2 time(s). Last edit at 08/13/2022 10:11AM by Dust.

Hi
Whether the X endstop is triggered or released, it shows "x_min: TRIGGERED" when send M119 note. Maybe this pin is broken. Thanks.

... could be, the I/O-pin is not correct assigned or defined (pull-up or -down).

For working without homing you have to invert the signal polarity (so it's not triggered anymore) and avoid homing/referencing ...

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Viktor
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I have found out the cause of the problem. The chip of the board is broken.