What was found
ELECTRICAL BURNING ODOR IN COCKPIT, FIRST AND BUSINESS. BURNING SMELL WAS CAUSED BY FAILED ROTOR SPIN BEARING IN COCKPIT STANDBY ATTITUDE INDICATOR (SAI). SHOP CONFIRMED SAI HAD OVERHEATED ROTOR BEARING. STATIC INVERTER (ON E1-4 SHELF) ALSO WAS FAILED. UNCERTAIN WHICH FAILURE OCCURED FIRST, BUT IT IS LIKELY THAT OVERHEATED SAI RESULTED IN FAILED INVERTER. SHOP HAS ONGOING PROJECT (BY ATTRITION) TO UPGRADE SAI'S BY REPLACING SPIN BEARING AND REDUCTION GEAR ASSY WITH MORE DURABLE CERAMIC MATERIAL. OVERHEATED SAI WAS NOT UPGRADED BEFORE FAILURE.