What was found
HF RADIO SIDETONE CUTS OUT INTERMITTENTLY DURING TRANSMISSION AIRINC REPORTS TRANSMISSIONS CUT OUT OCCASIONALLY PROBLEM EXISTS FROM BOTH AUDIO PANELS AND BOTH HF RADIOS. VHF RADIOS HAVE NO PROBLEM. OPS CHECK OF HF NR 1 AND NR 2 GOOD WITH POSITIVE SIDE TONE ON BOTH. NOTICED NR 1 SIDE TONE WEAKER. REPLACED REU OPS NORMAL. SIDE TONE ON NR 1 AND NR 2 MUCH BETTER. DUE TO HISTORY REPLACED NR 1 HF COUPLER. ALL OPS NORMAL. REF MM 23 51 01 23 11 61 000 801. ALSO REPLACED NR 2 HF COUPLER REF MM 23 11 61 000 801. GROUND OPS NORMAL.