What was found
AIR TURN BACK, ON CLIMB OUT, EN ROUTE, RECEIVED ADR NR 1 FAULT MESSAGE, SWITCHED TO ADR NR 3 AND LOST NAV DISPLAY AND PRIMARY FLIGHT DISPLAY INTERNAL REF INFO, TURNED BACK FOR REPAIR. MAINTENANCE REMOVED AND REPLACED NR 1 AIR DATA INERTIAL REFERENCE UNIT (ADIRU) IAW T/C R2A34304, OPERATIONAL CHECK WAS GOOD. FUNCTIONAL CHECK OF ADIRU S/N 2540 CONFIRMED FAILURE OF UNIT, PERFORMED THERMAL CALIBRATION AND ACCOMPLISHED SB 101-34-56 REPLACING THE PCB ASSEMBLY LOW VOLTAGE POWER SUPPLY AND MONITOR. TESTED IAW CMM TP1011, REV. 23.