slaved stepper problems

[Jonathan]

I am running it directly from the parallel port.

the motor will run quieter at a lower voltage, this is typical with stepper motors.

I suspected that, was just interested in checking the theory!

also you are running the 752 at 70V, this is the absolute maximum for this driver.I would advise to run it at a lower voltage.

I would advise myself that too, however I've checked it by connecting my oscilloscope to the MOSFETs (IRF540) whilst running and measuring the peak voltages at the points where it they switch under various conditions. There are no peaks above the rating of the MOSFETs, which is 100V, so I'm happy that it's safe.
That's no reason for anyone else to do the same, since each system will vary.

It looks like it must be the low voltage of your parallel port, but that still doesn't explain why the driver wouldn't work from the same pins on the parallel port that the other drivers worked with.