As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE OPERATING WITH AN IDG 2 INOPERABLE MEL APPLIED, APU GCU DISABLED AND APU GEN WAS NO LONGER TO POWER AC BUS 2. SINGLE GEN OPERATIONS. ELECTED TO AIR RETRUN. APU GCU RE-ENABLED ITSELF PRIOR TO LANDING. AIRCRAFT REMOVED FROM SERVICE. R & R APU GCU, IAW AMM 24-11-07. OPERATIONS CHECK GOOD. P/N: 720846D, S/N OFF: 4268, S/N ON: 4216.