As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PER SEAMC ACARS MESSAGE RECEIVED INDICATING POSSIBLE MALFUNCTION OF HF1 AND HF2 SYSTEMS. GROUNDED-YES. ACCOMPLISHED OPERATIONS CHECK OF NR 1 HF AND NR 2 HF AND FOUND NR 1 HF NOT TRANSMITTING OR RECEIVING. NR 2 HF OPERATIONS CHECK GOOD, REF B737-900 AMM 23-11-00. REMOVED AND REPLACED NR 1 HF ANTENNA COUPLER, REF AMM 23-11-61. OPERATIONS CHECK GOOD WITH NO FAULTS FOUND. GROUND VERIFICATION TEST SUCCESSFUL.