For a complicated description of a treadmill PWM (Pulse-Width-Modulation) controller you can visit http://www.freepatentsonline.com/6731082.html
You can visit wikipedia for a better definition of PWM. http://en.wikipedia.org/w/index.php?title=Pulse-width_modulation&oldid=71190555/
But basically (as best I can understand) it's an efficient speed controlling circuit that pulses the Voltage and the width of the signal to the motor off and on thousands of times per second. This transfers more power to the load and wastes less power to heat than a resistive type speed controller.
PWM style controller Trim Pots- located near one of the edges of the board.Each Set for specific motor MIN
(Minimum speed-Touch if you dare) adjusting MIN Trimpot may affect MAX, may be necessary to adjust both until desired levels are achieved MAX
(Maximum speed-Touch if you dare) Note that MAX adjustment may affect MINIR COMP
(Inrush compensation-Don't touch)Improves load regulation by providing minimal speed fluctuation due to changing loads. If the load presented to the motor does not vary substantially,the IR adjustment set at a minimum level. Excessive IR comp will cause control to become
unstable causing motor cogging. CL
(Current Limiting-Don't touch)The CL Trimpot sets the current which limits the maximum current to the motor. Also limits the AC line inrush current to a safe level during startup. ACCEL
(Acceleration Time Period, 0-full speed in seconds)I've never seen one on a treadmill circuit card, only on commercial PWM DC motor controllers. There must be something on the treadmill board that sets the time value..resistor perhaps?