As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CLT - FLT 729 - DURING CLIMB-OUT WITH ONE CSD ON MEL AND THE APU RUNNING, APU EXPERIENCED AN OVERSPEED AND SHUTDOWN. FLIGHT RETURNED TO CLT AND LANDED WITH NO FURTHER INCIDENT. MAINTENANCE REPLACED THE MULTI-SPEED ELECTRONIC SWITCH. (X)