As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BOTH UTILITY BUSES TRIPPED OFF ON SHUTDOWN. WHEN EXTERNAL POWER POWERING ACFT, DESELECTING EXT POWER TO TRANSFER POWER TO APU, BOTH UTILITY BUS TRIPS. BPCU REPLACED NO HELP. UTILITY BUS DOES NOT TRIP BETWEEN APU AND ENG GEN TRANSFERS. SUSPECT SLOPPY EXTERNAL POWER CONTACTOR. NO TIME TO T-S. IF NEEDED CONTACTOR: 563-0206. REPLACED CONTACTOR (K114) AND OP CHECKED GOOD.