Did this get resolved? I am experiencing the same issue. The screen no longer works on my treadmill, so I've wired in a Raspberry Pi into HD2 of the mc2100. I'm generating a 20Hz square wave from the PWM of the Pi. When i turn on the signal the motor starts running smoothly and LED is flashing normally, but after 5-10secs it slows down and stops, then a few seconds later it starts up and repeats the cycle.

Moderator edit: New threaded created from this.

 

Ensure the PWM is stable, trace the signal path using the MC2100 schematic previously posted here, there are several versions of this board, although some circuit paths are identicle

 

I have just realised that the wiring doc says the PWM signal driving the motor speed should be 5vdc, but the raspberry pi is generating a 3.3vdc signal. Perhaps i need to step it up to 5v to make it work properly

 

If you mean the PWM signal into pin 4 of HD2, it is the current that you have to warch, usually a series resistor is required to limit the curent into the Opto, to <50ma.