B737-700 FLC; DURING LAS IDALE RNAV DEP; HAS HDG DEV DUE TO AN FMC ANOMALY.

Narrative

CLRED LAS TO LAX RNAV IDALE 1 DEP. THE FO AND I VERIFIED ALL RNAV DEP PROCS ON CHKLIST COMPLIED WITH INCLUDING VERIFYING ALL FIXES; ALTS ON THE RTE PAGE OF THE CDU. DURING TAXI OUT; WE WERE CHANGED FROM RWY 19L TO RWY 25R. WE ENTERED THE NEW DATA IN THE CDU AND EVERYTHING LOOKED OK. AFTER TKOF; RNAV WAS ENGAGED AT 400 FT; AUTOPLT AT 1000 FT (CAPT FLYING). ACFT FLEW DEP NORMALLY. WE LEVELED OFF AT 7000 FT DUE TO ARR TFC DOWNWIND AT 8000 FT. THE LEVELOFF WAS BTWN ANDYY AND IDALE. XING IDALE; WE WERE GIVEN CLB TO 9000 FT AND I NOTICED THAT THE ACFT HAD ROLLED OUT ABOUT 210 DEGS. I INCREASED THE EFIS SCALE FROM 5-20 AND NOTICED THAT BOACH WAS NOT IN OUR SYS ON THE MAP OR THE CDU. I IMMEDIATELY ENGAGED THE HDG SELECT AND SET 150 DEGS. THEN I TOLD THE FO TO MANUALLY ENTER BOACH. THE SYS TRIED TO GO FROM IDALE DIRECT TO HECTOR. I DON'T KNOW WHY. ATC CALLED US ABOUT THE DEV AFTER WE HAD STARTED THE TURN TO 150 DEGS. I INFORMED THEM THAT OUR NAV COMPUTER HAD FOULED UP AND WE WERE TRYING TO RE-ENTER BOACH. THEY GAVE US A VECTOR TO JOIN THE BLD 210 DEG RADIAL. ZLA GAVE US A NUMBER TO CALL IN LAS DURING CRUISE. I EXPLAINED ALL THE ABOVE TO THE SUPVR AND HE TOLD ME THEY WERE SUBMITTING AN INTERNAL LAS ATC RPT. HE SAID THEY HAD OVER 100 RPTS GENERATED IN THE LAST 2 WKS. BOACH IS A FIX ON THE RNAV DEP NO MATTER WHAT RWY IS UTILIZED. I DON'T KNOW WHY IT WAS NOT IN OR DROPPED OUT OF OUR ACTIVE NAV BASE.