What was found
AIRCRAFT WAS GROUNDED: IN LEVEL FLIGHT AT 17,000 FEET, 290 KNOTS, WITH RIGHT AUTO PILOT ENGAGED, THE STABILIZER OUT OF TRIM LIGHT ILLUMINATED. PER QUICK REFERENCE HANDBOOK, YOKE ELECTRIC TRIM WAS INOPERATIVE. MANUAL TRIM UNUSUALLY DIFFICULT TO MOVE BUT WAS OPERABLE. FLIGHT AND LANDING UNEVENTFUL. EMERGENCY DECLARED. RETURNED TO PHL. REMOVED AND REPLACED STABILIZER TRIM MOTOR IAW AMM 27-41-71.