What was found
DURING START OF NR 2 ENGINE, N2 STOPPED AT 16% FOLLOWED BY A RIGHT ENGINE STARTER EICAS MESSAGE. SECONDS LATER APU SHUTDOWN. AIRCRAFT RETURNED TO BLOCKS. LINE MAINTENANCE INITIATED DEFERRAL MAINTENANCE ITEM-38063 MEL CAT C. AIRCRAFT RELEASED TO SERVICE. WHILE TROUBLESHOOTING APU DEFERRAL MAINTENANCE ITEM-38063 LINE MAINTENANCE REPORTED, WITH RT ENG START IAW AMM 71-00-00 & PACK RUNNING, SIGNS OF SMOKE IN COCKPIT. NO DAMAGE TO LT & RT ENGINES NOTED. EVIDENCE OF SMOKE APPEARED AFTER ENG SHUTDOWN. SMOKE ISOLATED TO BLEED AIR FROM APU. GENERAL VISUAL INSPECTION IDENTIFIED APU CASE DIFFUSER DAMAGE. CONDITIONAL INSPECTION-SMOKE OR FUMES IN COCKPIT SATISFACTORY. NO ADDITIONAL FAULTS FOUND . AIRCRAFT RELEASED TO SERVICE. WORK IN PROGRESS.