What was found
APU GENERATOR OVERHEAT WITH AUTO SHUTDOWN. SPARKS CAME OUT OF TAIL EXHAUST. SMOKE CAME OUT OF COMPARTMENT VENT AND GENERATOR VENT. MAINTENANCE INSPECTED APU COMPARTMENT FOR SIGNS OF HEAT DAMAGE. NONE NOTED. NO APU FIRE WARNING DETECTED ON FIRE DETECTION PANEL. FOR TROUBLESHOOTING PURPOSE, REMOVED AND REPLACED APU DC GEN IAW AMM TASK 27-33-06-00-801 AND 24-33-01-400-801. C/W OPS TEST OF APU 28U DC GENERATION SYSTEM IAW AMM TASK 24-33-00-710-801. OPS TEST GOOD. NO OTHER DEFECTS NOTED. AIRCRAFT RETURNED TO SERVICE.