Help with a usb BOB Spindle problems

[Doddy]

I'm inclined to agree with Jazz on this one...

From this image...,



The "10V" terminal looks to be the (input) supply to a charge-pump (simple RC) circuit, with the cap discharged through the switching of the local opto-isolator. There's a trace through a transistor that drives the AVI signal. My bet - this speed control is electrically isolated from the rest of the main board, and the ACM (gnd) AVI (0-10V output) - connect to the Spindle controller AVI (input) and 10V (*** INPUT TO THE BOARD ***) which needs to be connected to the 10V reference on the spindle controller.