The treadmill is a very popular piece of exercise equipment in the gym and in the home. Regular belt cleaning and belt lubrication will extend the life of the machine. When the belt speed begins to fluctuate or becomes erratic, there are some simple troubleshooting procedures you can perform yourself, though you may need to call a professional repairman to perform tests on the electrical components or the motor. Consult the owner's manual or the manufacturer's website for troubleshooting help.
Plug the treadmill directly into a wall power source. Do not use an extension cord, surge protector or power strip. The treadmill should not be sharing a circuit. Circuit sharing may cause inner component failure.
Disconnect the electrical power supply to the treadmill.
Clean the top surface of the belt using a nylon bristle brush and water. Dirt accumulation can rotate behind the belt, affecting the speed of the treadmill. Do not allow water to get under the belt. Allow the belt to dry completely before turning the power on.
Stand on the belt. Manually push the belt in the direction in which it normally moves. If you have difficulty turning the belt, there may be an issue with the belt/deck friction. If the belt turns freely, there may be an issue with the DC board output.
Reconnect the electrical power supply to the treadmill. Turn the power on. Watch the belt and note whether the speed fluctuates erratically (i.e., irregularly or inconsistently). If the speed fluctuates, there may be short in either the DC board or the motor. Use a multimeter to test the black and red lead wires that connect the motor to the power supply. An external power cord connects the motor the power supply.
Stand to the side of the treadmill; set the speed at 2.5mph and allow the treadmill to run. Note whether the speed is constant or if it varies. If the speed remains constant, step onto the belt. If the speed changes by slowing down or speeding up, there may be an issue relating to the output on the DC board that connects to the motor.
Check the signal generator. The signal generator is located in the upper panel. It sends a message to the lower electrical components that sets the correct speed. Increase the speed of the treadmill. Observe the speed. If the speed is erratic, there may be an issue with the signal generator.
Clean the top surface of the belt regularly to prevent dirt build-up behind the belt.