This morning before work I connected the driver board directly to the power supply, thus eliminating the switch and the current display. Again driving directly from the function generator it still glitched <8KHz (i.e. <1500mm/min).

I then checked the connections to the motor and they are all tight. Checked the coil resistance and they both read about 2.8 ohms. I think I read somewhere that this is OK.

I did notice that if the earth connection from the function generator is not made to the parallel port connector, (i.e. only pin3 square wave input is connected) then the stepper motors will still run. This must be earthing through the mains since the power supply and the function generator both run from the mains.

Therefore since the board can run from 24v - 33v, I'm thinking about running it from 2 small 12v batteries in series, as a test. The function generator can also run from batteries. This might tell me if there is some kind of earth loop problem, although Roy tells me that there should not be. The board is not optically isolated.

Are the other users of the DIYCNC system3 all-in-one board out there? What is your set up like?