Hi There.....check that lower motor control board for bulging or domed capacitors. If these large black capacitors are bulged up they are bad, and will cause less and less drive to that motor circuit, and more and more current to try to spin that motor, overworking the FET and other parts. You can contact jatinahATrocketmailDOTcom for repairs. Good luck!

Can be the motor or the motor control board faulty. You have to check the motor brush if it's OK the you should go for a new Motor control board.
if you wish to get some more details about treadmill repair then check the following link.
http://electro-medical.blogspot.com/