The t9500 treadmill will slow down in speed and increase in incline. i unplug it then it will behave for awhile, then it starts doing the slowing down and increase the incline.

https://www.youtube.com/watch?v=GAolnpKK3yM
The most likely cause for the motor to speed up and slow down is a dry or worn walking belt or walking board. Lift the walking belt and feel underneath for worn spots on the board. ... This mode also allows the technician to calibrate the speed and incline of the treadmill whenever a major electrical component is replaced.

Treadmill console needs to be replace

Hi, It's probably the speed censor. Clean it up and should be good to go. When you disasemble it clean all other parts and put back togeather. Good luck

This may well be either the
Console
LCB
Post wire

It sounds like you have a membrane issue. There are a number of different T9450 models and they all have slightly different consoles. You'll need your serial number to help pinpoint the parts you need. Your best bet is to go through the manufacturer (johnsonfit.com) and have them help you get the correct membrane and overlay.

http://www.youtube.com/watch?v=-oeXTKqWECw&feature=related

http://www.youtube.com/watch?v=GPI6dFJCUA4

http://www.youtube.com/watch?v=AZSMLpXm-tA&feature=related

Please see this videos and make this.Finally you have very strong 2 possibilty:1)Main motor 2) Control Board motor.

see the block diagram attached, and see how the main controller board has 90% aprox function of any treadmills. sincerely. G-d bless you

ernesto cuadra
managua, nicaragua. c.a

abrupt shutdown of the belt as the motor control detect a sharp increase in drive
current and inmediately stop driving belt.Some situation as jamming the belt may cause this error.Without such abuse should be a cause for extreme care and analysis for some Tech.

2 reason:

1) Motor drive; possible faulty(Test)

2) motor control board : possible faulty(Test)

Watch this videos tips:
http://www.youtube.com/watch?v=qgb2TY3WCkg&feature=related
http://www.youtube.com/watch?v=-oeXTKqWECw&feature=related
http://www.youtube.com/watch?v=GPI6dFJCUA4
http://www.youtube.com/watch?v=bF3OyQ3HwfU&feature=related
http://www.fixya.com/support/r10724803-measure_voltage_in_transforme_fitness
http://www.fixya.com/support/r10786838-test_procedure_dc_motor

Unplug unit remove motor shroud then start calibration procedure.
Press the Stop and the Speed Up keys down while inserting the safety key. If you cannot get into calibration then upper console needs to be replaced.
Press the Stop key one time. The Time window should read EP:2P. Some newer models may also say FP, Pass, or the like. This means that it passes the EPROM test. At this point if it show 2F FF or Fail then upper console needs to be replaced.
Press either incline key and the incline will calibrate automatically
BE CAREFUL, THE TREADMILL WILL RUN AT FULL SPEED IN THIS NEXT MODE! DO NOT STAND ON WALKING BELT.
Press the Speed Up key and hold it down until 85 is shown in the Distance window (some models may show the 85 number in another window).
If the top speed of the treadmill does not match the displayed speed on the computer console, adjust the max speed potentiometer (pot) on the motor control board. This is the board that the red and black motor wires connect directly into in the motor area. The Max Speed pot is clearly labeled.
The max speed potentiometer is a small square with a mobile center and is located in one corner of the board and is labeled MAX SPD. It is near the harness that carries the speed signal labeled H,W,L. Using a small insulated screwdriver adjust this potentiometer clockwise to speed up and counter-clockwise to slow down the max speed of the treadmill. A tiny turn of this potentiometer will make a big difference in speed so be careful when making adjustments.
It is not important to get the speed set exactly at the max speed of the treadmill but do make sure to get the speed within .2 MPH of the max speed of the treadmill. For instance if the max speed of the treadmill is 10 MPH, make sure to have the speed set between 9.8 MPH and 10.2 MPH. Some models have a 12 MPH top speed, so please check your manual if you aren’t sure.
After completing calibration of the speed, press the Speed Down key. The treadmill will automatically return to 0 MPH. Please allow the unit to stop completely before continuing.
Press the Stop key once and remove the safety key.

first thing to do is to enter the calibration mode. First remove and replace the safety key. Press and hold the elevation up and the speed down buttons until the machines beeps at you 3 times consecutively. You should also see either the model "9450" or the software code which varies from machine to machine. You should now see one of two things - "eng1" may be displayed in which case just use the elevation keys to get to "eng4" and hold enter for 3 seconds - then press start - this will calibrate your machine and confirm if there is any speed reading issues.

If your machine displays more numbers as it would on the deluxe and premier consoles of this brand then you should see the model of your treadmill at the top left. hold enter from here until "eng1" appears and the perform the steps as above. If the speed is not calculating properly during the calibration the magnet or the speed sensor may have been moved or the magnet could have gone bad - usually slowing to one speed and not changing is the sign of a bad speed sensor. If the control board had any irregular voltage it would shut down as a safety precaution.