What was found
(CAN) PRIOR TO DESCENT THE FLIGHT CREW REPORTED THE LOSS OF DIRECTION INFORMATION ON THE NR 1 HSI. FLIGHT CONTINUED TO DESTINATION WITH USE OF NR 2 HSI INFORMATION AND LANDED WITHOUT INCIDENT. MAINTENANCE WAS DISPATCH TO THE ACFT AND PROCEEDED TO TROUBLESHOOT THE NR 1 HSI SYSTEMS. HSI NR 1 AND NR 2 WERE SWAPPED AND THEN RETURNED TO THEIR ORIGINAL LOCATION AFTER THERE WAS NO CHANGE TO THE FAULT. THE NR 1 AND NR 2 DIRECTIONAL GYROS WERE THEN SWAPPED AND THE FAULT MOVED TO THE NR 2 POSITION. RETURNING THE DIRECTION GYROS BACK TO THE ORIGINAL POSITIONS AND THE FAULT ONCE AGAIN RETURNED TO THE NR 1 POSITION. NR 1 DIRECTION GYRO WAS REPLACED WITH A O/H UNIT AND WAS FUNCTIONED CHECKED SERVICEABLE IAW AMM, CHAPTER 34. ACFT RETURNED TO SERVICE.