What was found
PILOT REPORTED WHILE EN ROUTE, STAND-BY POWER OFF LIGHT ILLUMINATED. THE STAND-BY ALTERNATOR POWER WAS CHECKED AND STAND-BY POWER DID NOT COME ON LINE. MAINTENANCE WAS DISPATCHED TO THE AIRCRAFT AND CONFRIMED STAND-BY POWER FAILURE. THE STAND-BY ALTERNATOR SYSTEM WAS INSPECTED AND FOUND THE ALTERNATOR DRIVE SHAFT FAILED AT THE SHEAR POINT. THE STAND-BY ALTERNATOR DRIVE ASSEMBLY WAS REPLACED AND THE STAND-BY POWER SYSTEM WAS FUNCTIONALLY CHECKED AND NO DISCREPANCIES WERE FOUND. THE AIRCRAFT WAS RETURNED TO SERVICE.