I pretty much had everything working, and was doing the last set of calibration runs when, through my own fault, I had a small mishap. The servo was extending , but it was too close to one of the clips holding the glass down and the switch snapped off the arm. I reverted to the original firmware, mounted the switch back in its original location and printed a new arm.

I then started the ABL process from scratch, but was unable to control the servo using the M280 P0 Sxxx command, Thinking I had damaged the servo I tested it on an Arduino test setup and it worked. Many tests later and still no response to the command; however I found it would act correctly to the M401 and M402 commands, as well as to the G28 and G29 commands. In each case the servo raised and lowered the arm correctly, but still no movement from the M280 command.

Any ideas?