B737-300 FLT CREW HAS AN RNAV ANOMALY DURING THE BOACH 2 DEP FROM LAS.

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FLT FROM LAS ON THE BOACH 2 DEP. AT ABOUT 300 FT AGL ON TKOF; I NOTICED THE HSI COURSE POINTER SWING HARD L. CHKING THE LEGS PAGE; BOACH IS LISTED AT THE TOP. REBEL AND ROPPR ARE NO LONGER DISPLAYED. THE WX IN LAS IS VFR AND WITH NO XING TFC; DEP CTL WAS MORE THAN HAPPY TO CLR US DIRECT TO BOACH WITH A CLB TO FL190. LATER DURING THE FLT; ZLA GAVE US THE PHONE NUMBER FOR LAS TRACON. ON THE GND IN LAX; I CALLED AND TALKED TO THE SUPVR WHOSE CONCERN WAS THAT THIS WAS THE SIXTH COMPANY FLT IN 5 DAYS THAT HAS HAD AN RNAV DEP PROB. WHILE I WAS ON THE PHONE; I HAD LAX MAINT RUN A BITE TEST TO SEE IF IT SHOWED ANY FAULTS. NONE WERE FOUND. MY FO AND I ARE PRETTY SURE WE HAD THE FMC PROGRAMMED CORRECTLY AS A SIDE NOTE; FLT TO LAS 2 DAYS AFTER THE ABOVE EVENT; ACFT ON THE GRANPA ARR. WE WERE ASSIGNED A HDG OF 180 DEGS FOR A VECTOR TO PRINO FOR THE VISUAL APCH TO RWY 25L. WHEN APCH CLRS US DIRECT TO PRINO; IT'S 'EXEC' AND AIRPLANE STARTS A HARD R TURN TO THE NW; AT LEAST THAT'S WHAT THE COURSE POINTER WAS SHOWING. I DISENGAGED NAV AND CTL WHEEL STEERING BACKWARD TO THE S. MY FO PUTS PRINO BACK AT THE TOP OF THE PAGE AND 'EXEC.' NO HELP; PRINO STILL SHOWS OFF THE NW WITH A DISCONTINUITY BTWN PRINO AND LARRE. WE TRY LARRE AT THE TOP; SAME RESULT. WE TRY RWY 25L; SAME RESULT. EVERYTHING ACCORDING TO THE FMC IS OFF TO OUR R REAR SOMEWHERE. I GIVE UP ON THE NAV AND GO VOR TO INTERCEPT THE LOC.