As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE OPERATING THE APU WITH THE NR 1 GENERATOR PLACARDED INOPERATIVE, THE APU AUTO SHUTDOWN WHEN CLIMBING THROUGH 28,000 FEET. THE APU WAS RESTARTED AT 26,000 FEET AND THE AIRCRAFT LANDED WITHOUT FURTHER PROBLEM. THE APU FCU WAS FOUND LEAKING. THE APU FCU WAS REPLACED IAW MM 49-30-01. LEAK AND OPERATIONAL CHECKS WERE PERFORMED WITH NO FAULTS NOTED.