What was found
WHEN A/C WAS AT THE GATE AND PASSENGERS WERE DEPLANING CREW RECEIVED A SMOKE IN CABIN MESSAGE ON EICAS. THE CREW REPORTED THAT AFTER GROUND POWER WAS APPLIED AND RECIRCULATION FAN WAS TURNED ON, HAD SMOKE IN CABIN. EXTERNAL POWER WAS REMOVED AND ALL SYSTEM WERE SHUTDOWN AND REMAINING 4-7 PASSENGERS WERE RUSHED OUT OF AIRCRAFT. EMERGENCY WAS DECLARED. MAINTENANCE FOUND EXTERNAL POWER MODULE BURNED AND DEFERRED THE EXTERNAL POWER SYSTEM PER THE MEL AND RETURNED AIRCRAFT TO SERVICE. THE EXTERNAL POWER MODULE WAS REMOVED AND REPLACED.