What was found
SEA - APU STATUS MESSAGE NOTED IN FLT APPROX 30-40, AFTER SHUTDOWN, UNABLE TO START IN FLT. ABLE TO START IMMEDIATELY AFTER ARRIVAL SEA, PLACARDED APU START SYSTEM PER MEL 49-3A AUTH 2-69D-C ENTERED TO MIC-APU TO REMAIN ON THROUGHOUT FLIGHT. REMOVED AND REPLACED APU CONTROLLER PER MM. OPS CHECK GOOD APU STARTS ELECTRIC AND PNEUMATICALLY. REMOVED PLACARD MEL 49-3A AUTH NR 02-69D-C CLEARED MIC SHEET.