A B737-200 FERRY CREW IS SO ABSORBED IN AN ACFT EQUIP PROB THAT THE PIC OVERLOOKED A NAVIGATIONAL ERROR AND RPTED IN TO ATC OVER THE NEXT CHK POINT 8 MINS EARLY WHILE ON FREQ WITH COMMERCIAL RADIO; SFO; CA.

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WHILE ENRTE; BTWN COMPULSORY WAYPOINTS; MY FO AND I BECAME DISTRACTED DUE TO MULTIPLE ACFT SYS PROBS. THESE PROBS HAD THE POTENTIAL TO ADVERSELY AFFECT THE COMPLETION OF OUR FLT. BECAUSE WE BECAME SO PREOCCUPIED WITH OUR SYS PROBS; WE DID NOT REALIZE THAT WE WERE GOING TO ARRIVE AT OUR NEXT COMPULSORY WAYPOINT EARLY. AS WE CROSSED THE WAYPOINT; WE REALIZED THAT WE HAD ARRIVED 8 MINS EARLY DUE TO AN INCREASE IN OUR TAILWINDS. WE FAILED TO GIVE ATC VIA COMMERCIAL RADIO; PRIOR TO REACHING THE FIX; AN AMENDED ETA. (THE FO WAS HAND FLYING THE ACFT WHILE I WAS TROUBLESHOOTING THE SYS PROBS.) I PROMPTLY GAVE MY POS RPT TO COMMERCIAL RADIO; BUT WAS LATER QUESTIONED ABOUT THE 8 MIN DISCREPANCY. ATC VIA COMMERCIAL RADIO ASKED US IF WE HAD INCREASED OUR SPD. I RPTED; NEGATIVE; BUT WE HAVE PICKED UP SOME GOOD TAILWINDS. I REALIZED LATER THAT THE 8 MIN DISCREPANCY HAD ACTUALLY BEEN A 5 MIN ERROR DUE TO A CALCULATION ERROR I HAD MADE. IN CONCLUSION; THE SYS PROBS IN THE ACFT HAD DISTRACTED US SO MUCH THAT WE GAVE LESS ATTN TO OUR NAV AND TIME. ALSO; THE ACFT SHOULD HAVE BEEN PREPPED BETTER FOR THIS FERRY FLT.