SCT CTLR DESCRIBED AN INCIDENT WHEN FREQ WAS TEMPORARILY LOST; CAUSING A POTENTIAL CONFLICT ON FINAL FOR LAX AND RESULTED IN A GAR.

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WHILE WORKING DOWNE RADAR POS; I WAS RESPONSIBLE FOR ABOUT 4 ARRS TO LAX. I LOST USE OF THE PRIMARY FREQ 124.9 AT APPROX XA45. THE LAST CTL INSTRUCTIONS I ISSUED PRIOR TO RADIO FAILURE WERE TO ACR X TO FLY HDG 330 DEGS; DSND AND MAINTAIN 5000 FT. THIS IS BASICALLY A BASE LEG HEADING FOR TFC TO THE S COMPLEX AT LAX ARRIVING FROM OVER SLI VOR. THE HDG AND ALT PUT THESE ACFT IN CONFLICTION WITH ARRS THAT ARE STRAIGHT IN TO THE N COMPLEX. MY NEXT XMISSION FOR ACR X WAS TO TURN L HDG 280 DEGS; INTERCEPT RWY 25R LOC; DSND AND MAINTAIN 3500 FT. THIS INSTRUCTION WOULD HAVE BEEN A PRELUDE TO THE APCH CLRNC AND ALSO PROVIDED FOR SEPARATION WITH TFC ON THE N FINAL. NO RESPONSE FROM ACR X SO I SAY AGAIN. NO RESPONSE AGAIN. I TRY ANOTHER ACFT AND AGAIN NO RESPONSE. I NOTIFY THE OTHER FINAL CTLR WHO ISSUES INSTRUCTIONS TO CONFLICTING ACFT ON HIS FINAL TO EXPEDITE DSCNT WHICH ESTABLISHES SEPARATION BTWN THE TWO. MEANWHILE I UTILIZE THE EMER RADIO (ECVS) AND TURN ACR X TO INTERCEPT FINAL. NOW HE IS TOO HIGH TO COMPLETE THE APCH AND RESULTS IN A GAR. I ASKED THE SUPVR TO INCLUDE ON THE FACILITY LOG THAT THE REASON FOR THE GAR WAS BECAUSE OF THE RADIO FAILURE. THE FREQ WAS OUT FOR ABOUT 25 MINS TOTAL. MAINT TOLD THE SUPVR THAT IT WAS BACK BUT WHEN I TRIED IT I HAD THE SAME PROBS. 5 MINS LATER IT WAS BACK COMPLETELY. WE HAVE HAD NUMEROUS EQUIP ISSUES AT LAX AND SCT. I NEVER GOT AN ANSWER TO MY QUESTION ABOUT WHAT CAUSED THE FAILURE IN THE FIRST PLACE EXCEPT THAT A TECHNICIAN WAS OUT AT THE SITE WORKING ON A UHF FREQ AND PROBABLY FLIPPED THE WRONG SWITCH.