AN ACR CREW DISCOVERS THEIR COMPASS SYS TO BE UNRELIABLE. WITH ATC ASSISTANCE; A NORMAL ARR IS COMPLETED AS WX IMPROVES.

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FLT FROM RDU TO DTW. ON CLBOUT; OBSERVED 7-15 DEG DIFFERENCE BTWN CAPT AND FO COMPASS SYS. XCHKED STANDBY COMPASS AND FO'S SYS SEEMED OK. CAPT'S SYS OFF. FO COMPASS SYS. DRIVES CAPT HSI SO NO PROB FLYING ACFT. HDG DIFFERENCE FLUCTUATED ZERO-20 DEGS OUT IN CLB AND CRUISE. APPROX 100 NM E OF DJB; CLE CTR GAVE DIRECT TO DJB. IN TURN; WE OBSERVED FO HSI (CAPT'S RMI) LOCKED UP; THEN JUMPED L WHILE IN A R TURN. CAPT RMI (FO HSI) FROZE ON A 315 DEG HDG. CAPT HSI READ 290 DEGS; BUT STANDBY COMPASS SHOWED 220 DEGS. WE ADVISED CLE OF UNRELIABLE COMPASS SYS AND REQUESTED GYRO OUT PROCS. CONTACTED OUR AIRLINE DISPATCH AND MAINT CTL ON COM #2 TO ADVISE OF PROB. DTW HAD BEEN 2000 FT OVCST 1 1/2 SNOW. CMH WAS 6000 FT OVCST 10 MI VISIBILITY. DISPATCH ADVISED THAT DTW WAS IMPROVING -- 4000 FT OVCST 4 MI VISIBILITY; ALSO DTW APCH AGREED TO TAKE US ON GYRO OUT. WE AGREED TO CONTINUE TO DTW FOR 1 ATTEMPT. THEN MISSED APCH TO CMH (ALREADY OUR ALTERNATE; FUEL ON BOARD WAS MORE THAN SUFFICIENT). DTW WAS 6000 FT OVCST 10 MI VISIBILITY BY THEN; AND APCH WAS UNEVENTFUL. EXCELLENT COOPERATION AND COORD BY CLE ATC AND DTW APCH ALLOWED US TO COMPLETE THE SCHEDULED FLT SAFELY. ACFT WAS WRITTEN UP AND GNDED IN DTW. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE ACFT WAS TAKEN OUT OF SVC. IT HAD A PREVIOUS HISTORY OF SIMILAR PROBS THAT RESULTED IN MAINT REPLACING SOME WIRING AND FERROUS RIVETS AND SCREWS NEAR THE R FLUX VALVE. THIS FLUX VALVE WAS REPLACED AFTER THIS INCIDENT; AND THE ACFT RELEASED FOR SVC. SIMILAR PROBS CONTINUED TO OCCUR FOR THE NEXT MONTH WHEN TECHNICAL SPECIALISTS WERE CALLED IN TO DEMAGNETIZE OR REPLACE MORE RIVETS. PROBS CONTINUED UNTIL IT WAS FOUND THAT THE L FLUX VALVE WAS OUT OF ADJUSTMENT. AT THE TIME OF THE CALLBACK; THIS APPEARS TO BE THE FINAL FIX.