As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE ENROUTE, NR 2 RADIO DISPLAY UNIT FROZE AND CREW WAS UNABLE TO CHANGE COMM 1 OR COMM 2 FREQUENCIES USING RDU 1 OR RDU 2 AND STANDBY OR FMS TUNE BUTTON. CREW WAS ABLE TO STAY IN CONTACT WITH ATC USING 121.5. CREW ELECTED TO DIVERT. ACFT LANDED UNEVENTFULLY. MX FOUND NR 1 RADIO MANAGEMENT UNIT TO BE CAUSE OF DISCREPANCY. NR 1 RMU WAS REPLACED. OPERATIONALLY CHECKED SATISFACTORY AND ACFT WAS RETURNED TO SERVICE.