What was found
UNCOMMANDED YAW AT FL300, MACH .835, SMOOTH AIR F/O FELT RUDDER PEDALS MOVE WE WERE IN CRUISE FLIGHT AUTOPILOT ENGAGED. TROUBLESHOT IAW AMM 22-11-005-1 AND R & R LOWER YAW DAMPER RUDDER POWER UNIT COMPONENTS, HYD TRANSFER VALVE, HYD SOLENOIDE VALVE, TRANDUCER PER AMM 22-11-031-2, YAW DAMPER COUPLER PER AMM 22-11-121-4, LOWER RUDDER HYD PRESSURE SWITCH PER AMM 27-20-145. R & R UPPER YAW DAMPER RUDDER POWER UNIT COMPONENTS, TRANDUCER AND HYD SOLENOID VALVE PER AMM 22-11-031-2, CHECKED FOR HYD LEAKAGE, CHECK OK. TESTED SYS PER AMM 22-11-006-5 AND AMM 22-11-131-4, ALL TEST PASSED, A/C OK FOR SERVICE.