As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON DESCENT DURING APU START THE APU RPM INDICATED 116 PERCENT, THE APU "FAIL" ANNUNCIATOR ILLUMIATED, THE APU EGT INDICATED 24 DEG C AND THE APU MASTER CIRCUT BREAKER POPPED. THE APU WAS DEFERRED IAW MEL PROCEDURES AND THE TRIP CONTINUED. UPON RETURN, THE FAULT WAS TROUBLESHOT TO A DEFECITVE APU ELECTRONIC CONTROLLER. THE CONTROLLER WAS REPLACED AND CHECK IAW MM 49-40-00 AND THE ACFT WAS RETURNED TO SERVICE.