As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF, THE CREW ADVISED BOTH THE CAPTAINS HSI AND RMI INDICATORS ROTATED NORMALLY AND THEN FROZE ON A 185 DEGREE HEADING (AT 700 FEET AGL). AN EMERGENCY WAS DECLARED AND THE ACFT LANDED BACK AT DEPARTURE WITHOUT FURTHER INCIDENT. MX WOULD TROUBLESHOOT ACFT AND DUPLICATED PROBLEM. FOUND INOPERATIVE HSI. REMOVED INOPERATIVE HSI AND INSTALLED SERVICEABLE HSI IAW MM 32-40-00. OPS CHECKS WERE GOOD.