What was found
PHX - ABORTED TAKEOFF - FLT 792 - DURING TAKEOFF CAPTAINS AIRSPEED INDICATOR WAS FLAGGED AND NO AIRSPEED INDICATION. ABORTED TAKEOFF AT 90 KNOTS, RETURNED TO THE GATE IN PHOENIX WITHOUT FURTHER INCIDENT. MAINTENANCE REMOVED AND REPLACED NR 1 MACH AIRSPEED INDICATOR IAW BOEING 737-300 MM 34-12-21-424-05. OPERATIONAL TESTS WERE GOOD. TEAR DOWN REPORTS THEY COULD NOT CONFIRM FAULT HOWEVER DID REVEAL INTERMITTENT FLAGS THE 'N' POINTERS. UNIT WAS OVERHAULED WITH THE A/S MOTOR, DRIVER BOARD AND NEW 'N' POINTERS INSTALLED IAW CMM 34-12-02 REV. 1