DUE TO DATA BLOCK OVERLAPPING; TRACON FINAL APCH CTLR FAILS TO TURN AN SF34 ONTO PARALLEL FINAL AT DFW. THE SF34 CONFLICTS WITH AN MD80 BEING WORKED BY AN ADJOINING APCH CTLR SECTOR. THE SF34'S TCASII EVASIVE ACTION ALERTS FINAL APCH CTLR; AND BOTH ACFT ARE VECTORED ONTO FINAL APCH COURSES FOR LNDG.

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ACFT X; AN SF34; NWBOUND ON MODIFIED DOWNWIND; TOWARDS FINAL. ACFT Y; AN MD80; ON FINAL TO RWY 17C AT 5000 FT. HAD EQUIP PROBS WITH ANOTHER ACFT ON DOWNWIND. WHILE TRYING TO FIX THAT PROB; I FORGOT TO TURN ACFT X TO 350 DEGS DOWNWIND HEADING. ACFT X CONTINUED NWBOUND TOWARDS ACFT Y. TCASII HELPED RESOLVE THE DEAL AFTER THE ARR CTLR NEXT TO ME; ALERTED ME ABOUT ACFT X. I COULD NOT FIND THE ACFT FOR ALL THE DATA TAG OVERLAP ON FINAL. I BELIEVE; IF WE HAD COLOR SCOPES AS REQUESTED; I COULD HAVE FOUND ACFT X QUICKER; AND TURNED HIM TO AVOID A CONFLICT. SUPPLEMENTAL INFO FROM ACN 395758: A DATA TAG ON ACFT Y WOULD NOT SWAP OVER FROM A W DIRECTION TO AN E DIRECTION. THIS WAS SOMETHING MY TRAINER AND I WERE TRYING TO RECTIFY. THE PROB WAS NOT RESOLVED. THE FREQ HAD BLEED- OVER ON THE MAIN JUST PRIOR TO THE OCCURRENCE. WE WERE TRYING TO CHK THE STANDBY FREQ FOR BLEED-OVER. THE DATA TAGS WERE OVERLAPPING CONSTANTLY; SO THE SIT WASN'T RECOGNIZED UNTIL THE LAST MOMENT. CONFLICT ALERT DIDN'T ACTIVATE UNTIL THE ACFT WERE WELL INSIDE MINIMUM SEPARATION.