As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
GENERATOR 1, 2, AND 3 FREQUENCY WAS 406 AND NR 4 GENERATOR FREQUENCY WAS 398. GENERATOR NR 4 WOULD NOT PARALLEL CAUSING CIRCUIT BREAKER TO POP. CREATING SMOKE IN THE COCKPIT FROM THE MAIN CIRCUIT BREAKER. REMOVED AND REPLACED NR 4 AC CONTROL PANEL IAW MM 24-5-3. OPS CHECK ON GROUND OK IAW MM 25-5-0 ENTERED ON DMI 12403 PER MEL 24-1. (M)