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Makergear M2: Z Endstop Crashes Firmware

From a discussion on the Makergear 3D printer forums

A Makergear M2 user reassembled his printer, only to encounter a problem:

As soon as my z endstop triggers, the firmware resets

The Z endstop cable is plugged backwards into the RAMBo socket.

The RAMBo socket has three pins: [+ – S].

The two-wire switch cable ends in a three pin connector shell (*) with one empty contact. Unfortunately, the cable connector is not symmetric, not keyed to fit the socket latch, and easily fits into the RAMBo socket either way.

Plugged correctly, the two switch wires go to the [- S] socket pins, putting the [+] socket pin in the empty contact.

If the cable is plugged backwards, the two switch wires go to the [+ -] pins, putting the [S] pin in the empty contact.

Plugged backwards, when the switch trips, it shorts the power supply to ground. Unpleasant consequences ensue.

(*) I’d be unsurprised to discover a machine with a two-wire switch cable ending in a two-pin connector shell. Those must plug into the [- S] pins, leaving the [+] pin waving in the breeze.

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