What was found
CLT - FLT 1750 - EN ROUTE FROM PVD TO CLT, AIRCRAFT EXPERIENCED AN UNCOMMANDED ROLL IN CRUISE AT FL350, MACH .75. WITH B AUTOPILOT AND AUTOTHROTTLE ON AND UNAV AND LNAV ENGATED, THE YAW DAMPER DISENGAGED AND THE AIRCRAFT ROLLED 15-20 DEGREES LEFT. THE AUTOPILOT KICKED OFF AND THE CREW STABILIZED THE AIRCRAFT. CREW ATTEMPTED TO TURN THE YAW DAMPER BACK ON WITH AUTOPILOT OFF, BUT AIRCRAT ROLLED LEFT AGAIN. CREW THEN ATTEMPTED TO TURN ON BOTH A/B AUTOPILOT WITH YAW DAMPER OFF AND AIRCRAFT ROLLED AGAIN TO THE LEFT. CREW DID NOT DETECT ANY RUDDER MOVEMENT IN RUDDER PEDALS. CREW REQUESTED A LOWER ALTITUDE AND PROCEEDED ONTO CLT WITHOUT INCIDENT. NO EMERGENCY WAS DECLARED. MAINTENANCE FOUND THE RUDDER POWER CO