Mach3 Help required

[cropwell]

Actually, I believe it's the inputs that require the 12V-24V. The outputs should work with just the USB cable connected. At least that's how the one I have worked.

That doesn't quite make sense Gerry! The inputs are connected to the computer and require 5v/gnd to drive the buffer circuit. If the optocouplers have no buffering then the 5v is unnecessary as the LED in the opto is driven directly from the signals and ground connections in the D25 cable. You will then need 5v to bias the photo transistor in the output stage, which should be derived from a power source other than the computer 5v in order to give the galvanic separation.
The USB socket on this board connects through to two terminals labelled PC 5v and PC GND and these I just connect to the power supply 5v/GND - it works.

I probably have a spare one of these boards and if I find it I will have a poke round it with a meter.

I may not be 100% correct, but it ain't worth a dick slapping contest.

[Clive S]

For the sake of clarity for the op (Barry) the board need 5v and 12-24V with the grounds connected together to the BOB in order for the inputs and outputs to work. The USB is better not being used.