What was found
FLIGHT: 9148, UPON STARTING, RT ENGINE, AFTER SELECTING THE START SWITCH TO START, A LOUD SIZZLE CAME FROM THE FIRST OFFICERS SIDE PANEL, ALONG WITH A SMALL FLAME AND SMOKE. DETERMINED THAT AIRBORNE AUXILIARY POWER UNIT RELAY BOX AT FIRST OFFICERS SIDE PANEL HAD BURNED COMPONENTS, THE PROTECTION RELAY, BUS BAR HOUSING AND HARDWARE WERE REPLACED.