What was found
APU FAULT LIGHT ILLUMINATED ON START ATTEMPT AND FAILED TO START, PERFORMED APU BITE REF FIM 49-60 TASK 801 SHOWS FAULT MAINT MSG 49-41012. PERFORMED FIM 49-40 TASK 803 NO CURRENT FAULTS SHOWN ATTEMPTED APU START FAULT LIGHT ILLUMINATED AND NO APU START. APU BITE SHOWS NO ROTATION SHUTDOWN MAINT MSG 49-41012 AND MAINT HISTORY MAINT MSG 49-41297 START POWER UNIT SHOWS INTERNAL FAILURE. GROUNDED - YES. REMOVED AND REPLACED APU STARTER GENERATOR PER AMM 49-41-21. LEAK AND OPS CHECK GOOD. REMOVED AND REPLACED START POWER UNIT PER AMM 49-41-71 SPU INSTALLATION TEST GOOD.