As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AT FL 230, NR 1 CONSTANT SPEED DRIVE LOW OIL PRESSURE LIGHT ILLUMINATED. FLIGHT ELECTED TO RETURN DUE APU ELECTRICS WERE UNRELIABLE. REPLACED NR 1 CSD AS PER WORK CARD 1182-1. APU AND NR 1 CSD CHECKED SERVICEABLE DURING GROUND RUN.