What was found
(CAN) AFTER #2 ENGINE START THE #2 STARTER GENERATOR CAUTION LIGHT ILLUMINATED AS WELL AS THE D.C. BUS FAULT. CREW TRIED TO RESET BUT TO NO AVAIL. #2 ENGINE WAS SHUTDOWN. GROUND CREW APPLIED EXTERNAL POWER AND SMOKE BEGAN COMING FROM #2 ENGINE. #2 ENGINE STARTER CONTACT RELAY REPLACED DUE TO BEING ARCHED IN THE CLOSED POSITION. ALSO #2 ENGINE STARTER GENERATOR REPLACED DUE TO 2431-K2 RELAY BEING STUCK IN THE "START" POSITION CAUSING THE STARTER TO OVERHEAT. ENGINE GROUND RUN SERVICEABLE AND AIRCRAFT RETURNED TO SERVICE.