MAIN RADIO FAILED ON A ZID SECTOR AND BACKUP RADIO UNUSABLE. SUPVR RELEASED EQUIP TO MAINT WITHOUT FIRST INSURING ALL TFC WAS OFF THE FREQ.

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FREQ PROBS WITH 128.77 MAINS RELEASED TO AIRWAYS FACILITIES. WHEN OPENING NEW SECTOR; NEW CTLR ADVISED 128.77 STANDBYS NOT WORKING -- CONSTANT STATIC. BACKUP EMER COM WOULD ONLY COME ON 3RD PRIORITY AND DID NOT WORK IN THIS CASE. BECAUSE I WAS TOLD THAT 128.77 STANDBY WAS NOT WORKING; I RELEASED THE FREQ TO AIRWAYS FACILITIES. I FAILED TO ENSURE THAT WE TRIED TO GET THE ACFT OFF OF THAT FREQ. AS A RESULT; ACFT X AND ACFT Y WERE TFC ON A CONVERGING COURSE AND THE CTLR COULD NOT COMMUNICATE WITH EITHER ONE. ACFT X WAS EVENTUALLY RAISED ON 121.5; AND THROUGH ANOTHER ACFT THAT WE SENT OVER TO THE FREQ AND TURNED. BOTH ACFT Y AND ACFT X SAW EACH OTHER AND HAD TCASII. SUPPLEMENTAL INFO FROM ACN 578644: CTR FREQ LOST. ALL BACKUPS TRIED TO NO AVAIL. FINALLY CONTACTED ON EMER 121.5. ACHIEVED INITIAL VECTOR ACFT AND SIGHTING PRIOR TO RA. SUPPLEMENTAL INFO FROM ACN 578645: CTR FREQ LOST. TRIED ALL BACKUPS. FINALLY REACHED ACFT ON 121.5 BEFORE TCASII WENT OFF. ACFT ADVISED TFC IN SIGHT. ACFT DSND AND TURNED. SUPPLEMENTAL INFO FROM ACN 579094: INDY CALLED US ON 121.5 WITH TURN TO 250 DEG HDG. I SAW ACFT X ON TCASII AND VISUAL. HE WAS IN A L TURN DSNDING. I WAS IN A L TURN WHEN I GOT RA CLB. STOPPED CLB AT FL394. WENT BACK TO FL390. ACFT X HAD VISUAL ON US ALSO. SUPPLEMENTAL INFO FROM ACN 579237: AS A LINE CHK PLT ADMINISTERING TRANSOCEANIC OPERATING EXPERIENCE TO ANOTHER CAPT; NEW TO THE INTL FLYING CATEGORY; I HAD LEFT THE FLT DECK FOR A BRIEF REST BREAK IN THE CREW REST. WHEN ALMOST ASLEEP; I NOTICED AN UNUSUALLY QUICK THRUST REDUCTION; DSCNT; AND L TURN. UPON RETURN TO THE FLT DECK; THE OTHER CAPT ADVISED THAT ZID HAD EXPERIENCED A COM FAILURE ON THE PRESENTLY ASSIGNED FREQ. DURING THE PERIOD OF NO COMS; A TCASII RA RESULTED FROM PROX TO ANOTHER ACFT. THE RA DSCNT COMMAND WAS FOLLOWED AND THE TA'S TURN COMPLIED WITH. CREW WAS VISUAL ON CONFLICTING TFC THROUGHOUT MANEUVER. FLT RETURNED TO ASSIGNED ALT AND CONTINUED TO DEST WITHOUT INCIDENT. THANKS TO THE TIMELY RESPONSE OF THE CREW IN RESPONDING PROPERLY TO THE TCASII COMMAND; AND MONITORING OF GND FREQ (121.5) ON A SECONDARY RADIO; A MORE SERIOUS SIT WAS AVERTED.