This video covers troubleshooting of the Speed Sensor on the Stairmaster SC916 Stepper
Tools Needed: Multi Meter, 7/16" Wrench
A common misconception about battery powered units, it that it only requires you to step on the pedals to power the console; when in fact the speed sensor plays a major role in powering the console.
As shown in the video, if you step on the pedals and they fall to the floor due to no resistance and the console doesn't power up, you should check the speed sensor.
The speed sensor is mounted to the alternator and reads the speed sensor disc when the unit is pedaled producing an AC voltage. The voltage from the speed sensor can be tested at the connection of the speed sensor to the lower control board. The connection is a red and black wire. Using AC setting on your volt meter at its lowest range, place the red lead to the red wire and the black lead to the black wire. Make sure the leads of the volt meter are making a good connection. Now step on the unit and verify the voltage from the speed sensor. A good speed sensor will produce about 3 VAC before the console powers up.
If the voltage is not correct, inspect the adjustment of the speed sensor. It may be necessary to adjust the sensor closer to the speed sensor disc. Proper gap of the speed sensor to the disc is about the thickness of a business card.
Retest unit after making speed sensor adjustment.