What was found
DURING CRUISE FLIGHT, THE INSTRUMENT COMPARATOR LIGHT CAME ON IN FLIGHT WITH A 10 DEGREE SPLIT BETWEEN RMI'S. WHEN SWITCHING TO CAPTAIN'S OR FIRST OFFICER'S RMI HAD A 90 DEGREE SPLIT. AIRCRAFT RETURNED TO MSP AND LANDED WITHOUT INCIDENT. REPLACED THE INSTRUMENT SWITCHING UNIT, CONNECTOR D4883, SLAVING AMPLIFIER AND NR 2 RMI AND NR 1 DIRECTIONAL GYRO. OPERATIONALLY CHECKED NR 1 AND NR 2 COMPASS SYSTEMS, CHECKED OK.