As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF, THE CREW REPORTD THE FO EHSI AND THE CA RMI FROZEN AT 320 DEGREE HEADING. THE CREW PERFORMED AN AIR-TURN-BACK. MECHANIC INSPECTED THE AC BUT COULD NOT DUPLICATE THE PROBLEM. MECHANIC REPLACED THE NR 2 DIRECTIONAL GYRO FOR TROUBLESHOOTING AND RETURNED THE AC TO SERVICE. (K)