As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT DIVERTED TO JFK DUE TO NR 3 ENGINE GEN BUS TIE OPEN, FIELD OFF LIGHT ON. ZERO VOLTAGE ZERO FREQS. THEN NR 4 BUS TIE GEN OPEN FIELD OFF LIGHT ON, VOLTS AND FREQS NORMAL. REPLACED NR 3 GCU AND REPLACED THE RT BPCU BOTH ENGINES, OPS CHECKED OKAY AND ALL PARAMETERS NORMAL.