What was found
APU FAILED TO START ON DC POWER, WITH FAULT LIGHT. STARTS NORMALLY WITH EXTERNAL POWER CONNECTED. GROUNDED - YES. APU BITE PER FIM 49-60 TASK 801 SHOWED FAULT 49-41249 START CONVERTER UNIT SHOWS LOW BATTERY POWER LOGGING FOR EACH START ATTEMPT. ALSO FAULT 49-41297 START POWER UNIT SHOWS INTERNAL FAILURE LOGGING AS MAINT HISTORY LEVEL FAULT. T/S FOR FAULT 49-41249 PER FIM 49-40 TASK 822, BATTERY VOLTAGE AND WIRING CHECKS GOOD. REMOVED APU START POWER UNIT REF AMM 49-41-71-000-801. FOUND POTTING COMPOUND ON, AROUND, AND UNDERNEATH GROUND WIRE RING TERMINAL. CLEANED SPU RING TERMINAL AND REPLACED APU SPU PER AMM 49-41-71-400-801, OPS NORMAL.