PA34 ON VISUAL APCH HAD LTSS FROM DEPARTING GS. SYS ERROR.

Narrative

I CLRED PA34 FOR VISUAL APCH TO RWY 22 AT APF. I SWITCHED FREQS AND TERMINATED RADAR WITH HIM. RELEASED G2 OFF OF RWY 13 REF THE PA34. LOA WITH APF TWR ALLOWS THEM TO USE VISUAL SEPARATION FOR ARRS/DEPS (THEY HAVE NO RADAR/BRITE). I OBSERVED THE PA34 NE OF APF AND HE APPEARED TO BE HIGH (2000 FT). I CALLED APF TWR AND INQUIRED OF PA34'S INTENTIONS; THEY SAID THEY DID NOT KNOW AND THE G2 WAS ROLLING. I CANCELED PA34'S APCH CLRNC AND ISSUED HDG 130 DEGS AND CLB TO 2000 FT. APPARENTLY APF TWR RELEASED G2 WITHOUT ESTABLISHING VISUAL SEPARATION WITH PA34. IT APPEARED TO ME THEY MAY BE A POSSIBLE MIDAIR CONFLICT; SO I BROKE OUT THE PA34. HE RPTED CLBING TO 2000 FT AND WAS OBSERVED AT 2900 FT. THE G2 DEPARTED AND I BELIEVE THE PA34 MAY HAVE HAD INVALID MODE C BECAUSE HE APPEARED TO CONTINUE CLB UP TO 3700 FT. HE RPTED CLBING TO 2000 FT. I BELIEVE THIS SIT OCCURRED BECAUSE VISUAL SEPARATION WAS NOT APPLIED REF OUR LOA WITH APF (PER 7110.65) AND DUE TO (POSSIBLE) ERRONEOUS MODE C READOUT ON THE PA34. I TOOK CORRECTIVE ACTION TO AVOID WHAT I THOUGHT MAY BE A POSSIBLE COLLISION.