A B737-300 MAINT CTLR ALLOWED DEFERRAL OF THE TFC COLLISION AVOIDANCE SYS. RESULTED IN ATC XPONDER FAILURES.

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I RECEIVED A CALL FROM MAINT THAT ACFT X NEEDED 2 MEL'S FOR REPEAT PROBS. THE MECH I WAS DEALING WITH IS VERY KNOWLEDGEABLE AND TOLD ME TCAS AND GPWS WERE INOP AGAIN. HAVING ALWAYS HAD A GOOD WORKING RELATIONSHIP WITH THIS MECH; I ISSUED AN MEL FOR GPWS AUDIO INOP. I THEN ASKED ABOUT THE SECOND MEL AND HE SAID A REPEAT ON TCAS INOP AND THE BITE ON THE BOX SHOWED UPPER AND LOWER ANTENNAE FAULT. HAVING PULLED UP HISTORY; I CONFIRMED THE REPEAT WRITE-UPS FOR BOTH PROBS. WHILE ISSUING THE TCAS MEL; THIS MECH SAID HE HAD TO GO AND TURNED THE LOGBOOK OVER TO A DIFFERENT MECH; ONE I ALSO KNOW AND IS VERY KNOWLEDGEABLE IN AVIONICS. I ISSUED MEL 34-40 FOR TCAS WITH SP2 TO PULL THE CIRCUIT BREAKER. THE MECH QUESTIONED PULLING THE CIRCUIT BREAKER BUT DID NOT QUESTION MY REPEATED COMMENT OF TCAS INOP MEL 34-40. THE ACFT DEPARTED AND ENRTE TO ZZZ1; AND SHORTLY AFTER DEP; THE CREW CALLED DISPATCH TO RPT THAT ATC COULD NOT GET AN IDENT ON THEM AND THAT THEY THOUGHT ONE OF THE MEL'S WAS INCORRECT. DISPATCH CONTACTED ME AND THROUGH ACARS; I DETERMINED THAT MEL 34-40 SHOULD BE 34-18 FOR ATC. I INSTRUCTED THE CREW TO RESET CIRCUIT BREAKER FOR #1 ATC THAT THE MECH HAD COLLARED; WHICH THEY DID; BUT THE ORIGINAL PROB REMAINED; #1 ATC INOP; #2 ATC INTERMITTENT. THE ACFT CONTINUED TO ZZZ1 WHERE OUR MAINT WAS SENT TO CORRECT THE PROB. MY FAILURE IN THIS WAS NOT FOLLOWING OUR READBACK PROC. THE MECH'S FAILURE WAS NOT RECOGNIZING A TCAS MEL BEING ISSUED FOR AN ATC PROB. THE FLT CREW AND DISPATCH FAILED TO RECOGNIZE THE SAME THING. THE FIRST MECH HANDING OFF THE LOGBOOK IN THE MIDDLE OF THE DEFERRAL MAY HAVE HAD AN EFFECT. THE MECH BLAMED NOT HAVING A PAPER COPY OF THE MEL FOR REF.