pwm schematic help required please?

[Doddy]

Unfortunately much of what you are telling me is going over my head!
Does the fact the altering of the pwm voltage through mach3 commands makes no difference to the output from the controller board to the motor indicate a problem with the board itself?

No. In fact it's exactly as I'd expect from the information that you've supplied to date. If you was to set the speed to 10% of max (assuming you've calibrated it) then I'd expect the spindle to be OFF. And above about 25% I'd expect it to be full-on. This is simply the (wrong) application of the analogue output from the BOB to the opto-isolator input to the speed controller, which instead expects a PWM input.

Simply. Connect the BOB output pin P1 to ribbon Pin 3. Connect the Ground used for the BOB to ribbon Pin 4. There is no need for any of the resistors.

Rough-arsed sketch - the PC output pin-1 is a digital PWM output. The BOB routes this to two different outputs - the BOB "P1", which is a facsimile of the PC output - and is the signal you need. There's also an on-board (the BOB) integrator that converts the PWM to the analogue output, that you don't need. Your speed controller takes a digital PWM input and uses this either to generate the analogue drive to the onboard speed controller, or simply uses this to drive the onboard MOSFET to drive the spindle. Regardless, the important bit is that the speed controller around the pin 3/4 terminals is designed around having a Digital PWM input, and NOT an analogue input (which, confusingly, is derived from a PWM source)