As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING NR 2 ENG START RIGHT BUSS TIE TRIPPED. LOST LOWER EICAS, RIGHT BUSS OFF LIGHT ILLUMINATED. REPLACED NR 2 GCU, NO HELP. BPCU BITE SHOWS RIGHT BUSS FAULTS "BTB WIRING GCU". NEW BTB IN COCKPIT. REPLACED RT BTB, OP CHECKS GOOD PER MM.