What was found
AT CRUISE ALTITUDE, HEARD CLICK OR SNAP AND FELT ABRUPT JERK OF NOSE TO LT . RUDDER TRIM RAN AWAY WITH 50 PERCENT DEFLECTION AND STOPPED RETRIMMED RUDDER WITH NO FURTHER INCIDENT. CHECKED RUDDER CABLE TENSIONS AND DMU FOR A PCU FORCE FLIGHT. CONNECTED DMU AND FOUND NO INDICATIONS OF A FORCE FIGHT ON ANY PCU. REMOVED DMU AND RESTORED ACFT TO ORIGINAL POSITION CONFIGURATION. NEED TO LOCATE RUDDER CONTOUR BOARDS TO PERFORM RUDDER CONTROL SYSTEM CHECK.