What was found
FLT 1402, AUS-SFO, CLIMBING THRU FL 280, BLEED 2 LEAK AMBER EICAS MESSAGE ILLUMINATED (ENGINE BLEED SYS-SINGLE-NO ICING). RETURN TO AUS DUE NR 1 BLEED ON MEL. REF FIM 36-21-00-810-804A. REMOVED AND REPLACED BOTH AMS CONTROLLER PROCESSOR MODULES (CH A&B) AS PER AMM 21-00-01/401 MESSAGE CLEARED. NO FAULTS NOTED, RAN NR 2 ENG WITH BLEED AIR ON. NO EICAS MESSAGE NOTED. OPS CHECK OK.