What was found
UNABLE TO TRANSMIT USING HF-1 - CAN RECEIVE. RECEIVED PROLONGED TUNING TUNING TONE UPON INITIAL TRANSMISSION ATTEMPT AND LACK OF SIDE TONE THEREAFTER. GROUNDED - YES. PROBLEM DUPLICATED, SWAPPED HF R/T'S AND BOTH SYSTEMS WORKED. SWAPPED R/T'S BACK TO ORIGINAL SPOTS AND BOTH HF1 AND HF2 ETOPS GROUND FUNCTIONAL CHECKS GOOD IAW B737-800 AMM 23-11-00-710-801, OPS CHECKED NUMEROUS TIMES AND PROBLEM DID NOT RETURN. SYSTEM HAS RESET. HF1 ETOPS GROUND FUNCTIONAL CHECK GOOD IAW AMM 23-11-00-710-801.