As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
JUST AFTER TAKEOFF THE APU OVERSPEED LIGHT CAME ON AND THE APU SHUTDOWN. THE AIRCRAFT RETURNED AND LANDED, WITH NO FURTHER INCIDENT. REPLACED THE APU ACCESSORY UNIT AND THE THREE SPEED SWITCH. GROUND OPS CHECK GOOD AND AN OVERWEIGHT LANDING CHECK WAS COMPLETED. THE AIRCRAFT WAS RETURNED TO SERVICE.