A320 FLT CREW HAS A CABIN INTERCOM MGMNT DATA SYS (CIDS) FAILURE DURING APCH AND LNDG AT LAX.

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WE HAD AN FMC FAILURE ENRTE. WORKED THE PROB WITH MAINT OPERATING ON #2 FMC ONLY. IT TOO; HAD HISTORY OF MALFUNCTION. PER SOP; DISCUSSED PLAN B; C; D; ETC; IF LOSS OF #2 FMC OCCURRED. ON DSCNT; AFTER SEATING PAX AND PA BRIEF; NOTICED SEATBELT LIGHT ON ECAM SCREEN NOT ILLUMINATED. CHKED SCREEN AND CIRCUIT BREAKERS OK. NOTIFIED FO TO FLY ACFT WHILE I INVESTIGATED. THERE WERE NO ECAM WARNINGS TO INDICATE A FAILURE OF ANY SYS. SEATBELT AND NO SMOKING SIGNS NOT INDICATING ON; CALLED FLT ATTENDANTS TO QUESTION. DID NOT HEAR AUDIBLE 'DING' WHEN PRESSING CALL BUTTON. AFTER SHORT TIME; AS BRIEFED EARLIER WITH FLT ATTENDANTS FOR COM PROBS; I ANNOUNCED OVER PA FLT ATTENDANT PLEASE CONTACT COCKPIT. I HAD SIDE TONE BUT NO RESPONSE FROM FLT ATTENDANT. LEFT SEAT; SAW FLT ATTENDANT THROUGH DOOR; ASCERTAINED SECURITY OK; OPENED DOOR AND ADVISED COM FAILURE; BRIEF PAX; AND PREPARE FOR LNDG NOW; THERE WOULD BE NO OTHER COM. ADVISED HER TO KICK DOOR IF SHE NEEDED US. SHE SAID SIGNS WERE ON. BUSY TYPICAL LAX SWITCH RWYS AT A VERY BUSY TIME APCH. FO IN LOOP WITH FAULT. DISCUSSION IF SUB BUS FAILED WOULD WORK IT ON GND PRIORITY TO FLY AND LAND. AFTER LNDG; FLT ATTENDANT ADVISED SEATBELT SIGN OFF. NOTIFIED PAX TO REMAIN SEATED BUT PA EXTREMELY WEAK (RPTED TO ME BY AFT PAX). NEXT DAY; I CHKED MAINT ON ACFT AND SAW THAT 2 LEGS AFTER WE HAD OUR UNIDENTED FAULT; ACFT HAD CABIN INTERCOM MGMNT DATA SYS FAILURE. AT OUR WRITE-UP; OUR MECH FELT CABIN INTERCOM MGMNT DATA SYS EQUIP HAD LOST ITS PROGRAMMING AND HE RELOADED IT. SOMEHOW THIS FAULT SHOULD HAVE BEEN LISTED ON OUR ECAM. ALSO; THIS FAULT TOOK OUT ALL COMS BTWN COCKPIT AND CABIN. FLT INTERPHONE OR PA SHOULD BE SEGREGATED TO SEPARATE PWR SOURCES TO ALLOW COM. ALL SOP'S FOLLOWED AND COM WAS ESTABLISHED IN A PROFESSIONAL MANNER. EXCELLENT CLR DISCUSSION AND FLT COORD AT A VERY BUSY TIME. NO ATC DEVS; ETC. THIS IS ENTERED TO ALERT APPROPRIATE DEPTS OF ECAM FAULT NOT BEING PRESENTED; AND A NEED TO GET A DIFFERENT PWR SOURCE FOR BACKUP COM. FLT ATTENDANTS SAID THEY DID NOT HEAR PA CALL.