What was found
EN ROUTE SFO-FRA, CREW RECEIVED ADVISORY: BACKUP ELECTRICAL SYSTEM FAILURE. RETURNED TO SFO. *S/D* BOTH BACKUP GENERATORS FAILED. ORIGINAL GRIPES INDICATED INTERNAL ELECTRICAL FAULTS TO THE BACKUP GENERATORS. THEN, THE RIGHT BACKUP GENERATOR INDICATED A SHEARED SHAFT. BOTH BACKUP GENERATORS WERE REPLACED. THE MEL ACTION CONCERNING THE AD AGAINST A BACKUP GENERATOR SHEARED SHAFT WAS FOLLOWED. THE FINDINGS FOR THE BACKUP GENERATORS ARE AS FOLLOWS: (UAL P/N MR24250-506 AND MR24250-379 OR MFG P/N 20VSCFGEN01). 379 MAIN ROTOR ANTI-DRIVE END BEARING SURFACE FAILED. 506 THE EXCITER ROTOR LEAD WIRES BROKE ON THE MAIN ROTOR. COMPONENT TOTAL TIME AND CYCLE ARE NOT AVAILABLE FROM UNHI.