As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX- CLIMBING THROUGH 10,000 FEET, FLIGHT ATTENDANT REPORTED THAT SMOKE ALARM IN LAVATORY WAS SOUNDING AND THAT SMOKE WAS VISABLE. TURNED OFF APU IN FLIGHT AND SMOKE WAS DISSIPATING. AIRCRAFT RETURNED TO FIELD AND LANDED WITHOUT INCIDENT. REMOVED AND REPLACED APU. OPERATIONAL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.