PHL CTLR PROVIDING OJT EXPERIENCED NEAR LOSS OF SEPARATION WHEN STUDENT FAILED TO COMPLY WITH BOUNDARY SEPARATION REQUIREMENTS.

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I WAS TRAINING ON 3 POS COMBINED. TRAINEE WAS CLOSE TO CERTIFICATION THROUGHOUT TRACON BUT THIS WAS HIS FIRST HRS ON THIS POS. ACFT X CAME OFF OF RWY 9L AT PHL AND WAS CLBED TO 12000 FT. ATTN WAS THEN FOCUSED ON A DIFFICULT SITUATION 40 MI AWAY ON THE OPPOSITE END OF OUR SCOPE. ACFT X CLBED QUICKLY AND WAS TURNED R ON COURSE ABOUT 15 MI E OF PHL. THIS IS ON THE EDGE OF OUR BOUNDARY WITH ZDC. THEY HAD STARTED AN EWR/LGA ARR DOWN EARLY TO 12000 FT. SO THEY WERE ON THE EDGE OF THEIR SPACE AND WE WERE ON THE EDGE OF OURS. ACFT X HAD A TCASII 'ADVISORY' NOT AN 'RA' ON THE TFC. SEPARATION WASN'T LOST BUT IN ANOTHER MIN IT WOULD HAVE BEEN. I ALSO DIDN'T SEE THE LIMITED DATA UNTIL LATE BECAUSE WE HAD MY DEVELOPMENTAL'S 'PREFERENCE SET' UP ON STARS. MY LESSONS: CHK ALL 'PREFERENCE SETS' BEFORE TRAINING. DON'T TRAIN COMBINED EARLY IN HRS. DON'T FEEL CONFIDENT BECAUSE DEVELOPMENTAL IS CONFIDENT ON OTHER SECTORS. SCAN MORE. FINALLY ISSUE INSTRUCTIONS THAT CAN'T BE AFFECTED BY CLB RATE OR WIND DIRECTION. ALL THINGS I KNOW OR SHOULD HAVE KNOWN. ALSO; I DIDN'T SLEEP WELL LAST NIGHT AFTER A QUICK TURN. I SHOULDN'T BE TRAINING WHEN I'M NOT 100%.