I have been using DC42's Mini Differential IR height sensing board successfully for a while but yesterday I did some maintenance on my printer and the probe no longer works correctly.
I get the 4 flashes on startup but the sensor readout on the Duet 2 board stays at 456 for the z probe readout, the LED lights when I put a surface close to the probe but the readout stays the same. Any ideas"

M558 P1 X0 Z0 F120 T6000 ; Set Z probe type to modulated, the axes for which it is used and the probe + travel speeds

G31 P500 X11.0 Y5 Z0.6

Bob

Most likely the wire between OUT on the IR sensor and the IN pin on the Duet Z probe connector has broken.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].