What was found
THE PILOTS REPORTED HEARING A C-CHORD CHIME AND THE NR 2 CHANNEL PITCH AND ROLL 'OFF' LIGHTS ILLUMINATED ON THE AUTOPILOT STATUS PANEL. THE PILOT ALSO NOTED THAT THE ESSENTIAL POWER 'ALTN' LIGHT FLICKERED WHEN THIS OCCURRED. MAINTENANCE SUSPECTED THE NR 1 AC BUSS VOLTAGE/FREQUENCY SENSOR FAULTY. THE DISCREPANCY WAS CONFIRMED AND CORRECTED BY REPLACIING THE NR 1 AC BUSS VOLT/FREQ SENSOR.