EE WAS INSTALLING REPAIRED LIFT CYLINDER ON A 750 JOHN DEERE TRACKHOE HE POSITIONED A LADDER AGAINST THE BOOM OF THE EXCAVATOR AS THE CYLINDER WAS LIFTED UP AND CLOSE ENOUGH FOR HIM TO REACH THE LADDER STARTED TO SLIDE ALONG THE BOOM OF THE EXCAVATOR HE THEN LOST HIS BALANCE AND FELL AND STRUCK THE REAR BUMPER OF SERVICE TRK RESULTING IN PAIN TO LEFT SHOULDER