As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 1 THRUST REVERSER UNLOCK WARNING ILLUMINATED SHORTLY AFTER TAKEOFF. STAYED ON APPROXIMATELY 15 MINUTES THEN EXTINGUISHED. THE FLIGHT RETURNED TO MSP AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED THE REVERSER UNLOCK SWITCH. SUBSEQUENT FUNCTIONAL TEST WAS SATISFACTORY.