It could be a couple things. first I'd check and make sure you have propper alignment of the rpm sensor and that it's actually functioning. There should be an LED on the lower board that should light up every time the magnet on the front roller passes by the sensor. If that's good it could be your motor brushes but make sure you unplug the unit before checking. They should have atleast 1/4" left and that would even be low. Those sound like the first possible causes as the lower board is trying to turn the motor so it doesn't sound like a board issue. I'm at fitfix&shaw.ca if you need more help.
Jamie
November 2009