MD83 CREW DEVIATED FROM THE LAX SEAVU ONE STAR AFTER A RWY CHANGE AND DIFFICULTY WITH THE FMC ACCEPTING THE NEW RWY INPUT.

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DURING SEAVU ONE ARR (TNP TRANSITION) WE WERE CHANGED FROM RWY 25R TO RWY 24R. I WAS FLYING; SO COPLT ATTEMPTED TO CHANGE THE RWY. WE HAD DIFFICULTIES WITH THE ARR FUNCTION DURING PREFLT (THE ARR SECTION WHEN THE DEP/ARR BUTTON WAS DEPRESSED WOULD NOT COME UP); SO I WAS ANTICIPATING DIFFICULTIES WITH THE RWY CHANGE. COPLT ENTERED THE CHANGE AND ASKED ME TO VERIFY WAYPOINTS. I WAS FLYING AND TRYING TO STAY AHEAD OF TURN REQUIREMENTS; TOOK A QUICK SCAN OF THE STAR (A VERY BUSY STAR) AND I MISSED THE WAYPOINTS HE HAD ENTERED (WHICH; IN RETROSPECT; WERE CORRECT) AND STATED I THOUGHT THEY WERE INCORRECT. HE PROCEEDED TO REENTER. I WAS BEHIND THE ARR AND THOUGHT WE WERE STILL BEFORE THE TURN AT MINZA AND CHANGED FROM THE ILS BACK TO POM 278. BOTH COPLT AND APCH QUERIED MY COURSE AND ALT. APCH TURNED US BACK TO 180 DEGS FOR INTERCEPT OF RWY 24R; LEVELED US AT 7000 FT AND THEN CLRED US FOR THE APCH UPON INTERCEPTING. LNDG WAS UNEVENTFUL. I CALLED TRACON. SUPVR RPTED NO CONFLICT/NO PROBS WITH OTHER ACFT. LOTS OF REAL POTENTIAL FOR SERIOUS CONSEQUENCES DURING MY LOSS OF SITUATIONAL AWARENESS. I AM REEVALUATING PRIORITIES; NAVAID BACKUP; ADVANCED THOROUGH STUDY OF APPLICABLE STARS AND POTENTIAL CHANGES; ALTS DELINEATED BY BALL NUMBERS AND BRIEFING MY PARTNERS TO ABANDON DISTRACTING PROGRAMMING OF FMS IF IT JUST ISN'T WISE FOR THE SITUATION.