As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ETOPS FLT 478 KOA-OAK. AFTER THE NR 2 HF PASSED THE FLIGHT VERIFICATION FROM FLIGHT 477 (PREVIOUS FLIGHT LEG), THE NR 2 HF LATER BECAME UNABLE TO TRANSMIT DURING CRUISE FLIGHT. CREW CONTINUED TO OAK WITHOUT FURTHER INCIDENT. MAINTENANCE REMOVED AND REPLACED THE NR 2 HF COUPLER PER AMM 23-11-61-4 AND COMPLETED OPERATIONAL CHECKS. AIRCRAFT WAS RETURNED TO SERVICE AND PLACED ON FLIGHT VERIFICATION. AIRCRAFT PASSED FLIGHT VERIFICATION.