What was found
APU FAULT LIGHT AND MAINTENANCE LIGHT. ACFT GROUNDED. R & R THE APU STARTER GENERATOR UNIT REF AMM 49-41-21. ETOPS SIGNIFICANT ITEM PART VERIFIED. NO FIX, PROBLEM REMAINS. APU STARTER GENERATOR STILL REQUIRES AN OPS CHECK AND LEAK CHECK. PLEASE PERFORM AMM TASK 49-41-21-710-001 FOR START/ GENERATOR INSTALL TEST AND LEAK CHECK. TROUBLESHOT FURTHER REF FIM 49-40-806, SUSPECT FAULTY APU START CONVERTER UNIT, REPLACED STARTER CONVERTER UNIT. FOR CONVERTER UNIT PN 1152466-250, SN 1152466-00767, REF AMM 49-41-61. NO FIX. REINSTALLED STARTER CONVERTER UNIT, SN 1152466-01564. REPLACED APU START POWER UNIT REF MM 49-41-71. APU WILL NOT START. APU BITE SHOWS MAINTENANCE MESSAGE 49-41244, "GENERATOR DIODE FAIL SHUTDOWN". ACCOMPLISHED RESET FOR FAULT 49-41244 IAW FIM 49-40, TASK 806, PARA A5 AND PERFORMED FAULT ISOLATION IAW PARA F. ACCOMPLISHED TEN START/SHUTDOWN CYCLES WITH NO FAULTS. IAW FIM PARA F 2, D, 8, FAULT 49-41244 IS NOT ACTIVE. PERFORMED STARTER-GENERATOR INSTALLATION TEST IAW MM 49-41-21-400-801. OPS NORMAL, NO LEAKS NOTED. PERFORMED START POWER UNIT INSTALLATION TEST IAW MM 49-41-71-400-801. OPS NORMAL. PERFORMED APU OPS TEST IAW MM 49-11-00-710-801, ALL TESTS PASSED.