What was found
CAPTAIN REPORTED AHRS 1, 2 AND 3 BASIC MODE LIGHTS TURNED ON. AHRS 1, 2 AND 3 BREAKERS WERE RESEATED AND AHRS 1 AND 2 WORKED CORRECT BUT AHRS NR 3 FAILED, SO IT WAS DEFERRED IAW MEL 34-38. AIRCRAFT WAS DISPATCHED BUT RETURNED TO PLATFORM DUE TO THE SAME FAILURE. THE FLIGHT DIRECTOR BARS WERE CHECKED BEING CORRECT AND AIRCRAFT WAS DISPATCHED WITH THE 1, 2 AND 3 AHRS´S IN BASIC MODE. DURING OVERNIGHT CHECK, WIRING WAS CHECKED, BREAKER B10-407 AND RELAYS R20-92 AND R20-91 WERE REPLACED IAW WDM 34-24-01 AND TESTED IAW MM 34-24-00, ALL CORRECT.