ZLA CTLRS EXPERIENCED OPERROR AT FL230 AS RELIEVING CTLR ISSUED DSCNT; NOT OBSERVING CONFLICTING TFC WITH LIMITED DATA BLOCK.

Narrative

E120 WAS NOT DISPLAYED ON SCOPE DURING RELIEF BRIEFING AND NOT KNOWN AS TFC. I ASSUMED POS AND DSNDED A318 AND DID NOT SEE ANY TFC AS A FACTOR. THE LIMITED DATA BLOCK WAS NOT SEEN; BUT THERE. THE CONFLICT ALERT ALERTED AND BROUGHT UP THE E120 DATA BLOCK AS TFC. I ISSUED A TURN TO THE A318 WHO THEN INFORMED ME HE WAS RESPONDING TO RA AND CLBING. THE E120 WAS NOT BRIEFED AS TFC; NOR DID I OBSERVE THE LIMITED DATA BLOCK. THE CTLR BEING RELIEVED TOOK OVER THE D-SIDE POS SINCE THE E120 DATA BLOCK WAS NEVER DISPLAYED ON THE SCOPE DURING MY BRIEFING. I DID NOT SEE THE TFC. SUPPLEMENTAL INFO FROM ACN 671290: A CTLR IN TRAINING WAS ASSIGNED TO THE RADAR POS THAT COULD NOT WORK THE POS BY HERSELF. I BRIEFED HER ON THE POS AND THEN MOVED TO HER ASSISTANT OR D-SIDE POS. I HAD SOMEHOW INADVERTENTLY TAKEN THE DATA BLOCK OFF ONE OF THE AFFECTED ACFT (E120) OFF OUR SCOPE AFTER THE NEXT SECTOR HAD ACCEPTED THE HDOF. WHEN THE RADAR PERSON DSNDED THE A318; CONFLICT ALERT ACTIVATED AND FORCED THE DATA BLOCK OF THE E120 BACK ON OUR SCOPE. THE R-SIDE TURNED THE A318 20 DEGS TO THE R; BUT AT POINT THE ACFT WERE SIDE-BY-SIDE WITH APPROX 34 MI SEPARATION.