What was found
EICAS MSG.-DATALINK LOST DISPLAYED VHF DATALINK LOST ACARS NO COMM DEBRIEFED CREW AND WAS TOLD 1.5 HOURS INTO THE FLT GOT AN INTERMITTENT DATALINK EICAS MESSAGE BUT THEN THE DATALINK WENT OFFLINE COMPLETELY WHILE OVER THE NORTH ATLANTIC. ACARS MESSAGES MADE NO SENSE. AT THE GATE ALIGNED & WAS ABLE TO INIT ACARS & SEND MESSAGES TO TOMC WHICH WERE RECEIVED. WAS NOT ABLE TO RECEIVE MESSAGES BACK. REF FIM 23-22 FAULT TREE 858. COMPLETED FIM 23-22 TASK 858. NO DEFECTS NOTED. PERFORMED FIM 23-12 TASK 802 AND FOUND NR 3 VHF TRANSCIEVER WOULD NOT TEST. NO LIGHTS, NO RESPONSE. R & R NR 3 VHF TRANSCIEVER IAW AMM 23-12-01. OPS CHKD GOOD.