As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEVEL AT FL 310 IN SMOOTH CONDITIONS, EXPERIENCED A THREE LIGHT TRIP. RAN QRH PROCEDURES, UNABLE TO RECOVER BTB, G/B OR FIELD. FREQS/VOLTS ON NR 2 GEN WERE ZERO (OFF SCALE LEFT). NO LIGHTS ON ELEC FAULT PANEL ILLUMINATED. NR 2 CSD WAS DISCONNECTED. AIR TURNBACK. UNABLE TO POWER NR 2 AC BUS. REMOVED AND REPLACED NR 2 CSD IAW 727-200 M/M 24-10-011-4 AND REMOVED AND REPLACED NR 2 GEN IAW 24-20-001-4 OP AND LEAK CHECKED GOOD.