Treadmill (Vision Fitness T8500) turns on, motor doesn't run...

Open motor shroud and inspect all connection on the motor control board see if all LED 's are lit except that light up when incline motor is moving up or down. then check the two connector coming from the drive motor to the board sometime over time the two connector will have a cold soldier I would move them to see any excessive movements of the pins then hit start and see if there is any belt movement. Last but not least unplug unit and check the motor brushes if they are less than 3/8 in in length replace them. Call them @ 1-800-335-4348 they under their parent corp. Johnson fitness.

I had the same problem. I even ordered a $300 controller board. The new board didn't work either. That's when I started checking voltages from the control board to the motor. That was good. Lastly I checked the brushes. Almost nothing left. . . The motor started working again after I put everything back together. I need to order new brushes and return that contoller board.

You can get new brushes here
http://www.partsfortreadmill.com/parts-for-treadmill/treadmill-motor-replacement/treadmill-motor-brushes-20x9x22-h-mm.html

and you can check here for treadmill help in general
http://www.treadmillsrepair.co.uk/
http://www.partsfortreadmill.com/repair/repair.htm