As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT#1621, LHR-BOS. (ETOPS) WHILE T/S FOR APU CLASS II MSG FOUND AC GEN CLASS II MSG FROM IDG 2 & HAS HISTORY; PERFOMRED TSM 24-00-00-810-829-A. REMOVED AND REPLACED GCU2 AND PERFORMED WIRING CHECKS AND ALL CHECKS PASSED. REF AMM 24-21-01 PERFORMED BITE OF GAPCU AND ALL TESTS PASSED OPS CHECK GOOD AT THIS TIME.'