What was found
ON TAXI IN, STARTED APU BOTH ENGINES RUNNING BATTERY DISCHARGE LIGHT ILLUMINATED FOR 30 SECONDS. DURING START SEQUENCE THE WENT OUT. ALSO OCCURRED IN GATE WITH GROUND POWER CONNECTED DURING START SEQUENCE. ACFT GROUNDED. UPON START, FOUND THAT BATTERY DISCHARGE LT ILLUMINATED MOMENTARILY, ALSO FOUND FAULT CODE 49-41250 ON CURRENT STATUS IN CDU, START CONVERTER UNIT SHOWS START SYS INOPERATIVE. R & R STARTER GENERATOR, REF MM 49-41-21. OPS & LEAK CHECKED GOOD. ONCE APU WAS STARTED NO BATTERY DISCHARGE LT AND CDU SHOWED FAULT CLEARED & NO FAILURES IN CURRENT STATUS.