You have a short in something.
Disconnect the motor wires.
Start The treadmill, if the fuse stays something is wrong with the motor or motor wires. If the fuse blows your may have a bad lower board.
When the fuse blows does the display stay lit.
How do you know the motor brushes and lower board are good ?
You can e-mail me at markepeterson@austin.rr.com
this may take a while.
Mark Peterson
April 2008