Touch Probe weirdness

So I finally got around to installing the touch probe over the holiday.

Wired up the probe to my 2.1 Shapeoko 3 board. GRBL 1.1 upgrade already installed, Running CM 4.0.428 on a Windows 10 PC.

With the Shapeoko powered up but NOT connected to CM, the touch probe led is green, and it turns red when I touch it with the alligator clip lead. So far, so good.

Next, I fire up CM and connect to the Shapeoko. Touch the alligator clip to the probe body, LED goes to red. Good.

Click “Initialize Machine” in CM, and it homes the gantries.
Touch the alligator clip to the probe body: NO RED. It just sits there solid green.

Shut down CM, but leave the Shapepoko on. Touch the clip to the probe, no red.

Power down the Shapeoko, then power back up. Touch the clip to the probe => RED LED.

When installing the probe, I first attached the alligator clip to the shapeoko through one of the screws at the corner of the controller pcb. When I powered up, CM could not find the shapeoko at all. So I backed that out and attached the alligator clip to the aluminum shroud around the PCB, using a self-tapping sheet metal screw.

Any ideas why the probe stops working after CM machine init?

just a guess, but maybe somehow it is no longer properly grounded when it moves to different positions?

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Is this repeatable?
Maybe a bad ground? Can you just ground the clip to the board ground? Any chance the shroud has a clear coating (non-conductive) on it?

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100% repeatable after each power cycle. 100% non-responsive after CM machine init.

Can you just ground the clip to the board ground?

Ok. Where is the board ground?
I tried attaching the lead to the mounting screw in the top right (facing the back of the Shapeoko, 2.1) of the controller board, but then CM couldn’t find the shapeoko at all.

.Any chance the shroud has a clear coating (non-conductive) on it?

Perhaps, but the screw goes clear through the sheet metal.

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Two pins to the right of the 5v pin on the ICSP header. (That’s the 6pin, 2x3, header near the power connector)

Every other pin in the row of connectors that includes the limit switches and probe.

Yours does.

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