CMH CTLR DESCRIBED SUSPECTED ACFT XPONDER FAILURE DUE TO LACK OF BEACON TARGET BUT CONFIRMED OTHER LCL RADAR WAS DISPLAYING TARGET.

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I WAS WORKING THE N RADAR ACFT X; A PA34/I; WAS HANDED OFF TO ME APPROX 15 NM SW OF CMH AT 7000 FT. S RADAR ADVISED THAT THE ACFT'S XPONDER HAD BEEN INTERMITTENT. THE ACFT'S RTE WAS DIRECT GVQ; WHICH PUT IT ON A NORTHEASTERLY TRACK THAT WOULD TAKE IT NEARLY DIRECTLY OVER CMH. UPON INITIAL CONTACT THE PLT INQUIRED AS TO HOW HIS XPONDER APPEARED. I ADVISED THAT THERE WAS NEITHER MODE C ALT NOR A XPONDER BEACON RETURN DISPLAYED. ALL OTHER TRACKED ACFT ON OUR STARS DISPLAYS; WHICH UTILIZES OUR CMH ARPT SURVEILLANCE RADAR (ASR-9...MODE S); APPEARED JUST FINE. HOWEVER; HAVING EXPERIENCED INTERMITTENT XPONDERS IN THE PAST; I ALWAYS MAKE IT A POLICY (NOW THAT WE HAVE THE CAPABILITY WITH OUR STARS EQUIP) TO SWITCH TO THE LONDON OHIO AIR RTE SURVEILLANCE RADAR (QWO ARSR) TO COMPARE. IF BOTH SHOW A PRIMARY TARGET ONLY; I CAN STATE WITH ABSOLUTE CERTAINTY THAT THE ACFT'S XPONDER IS INOP. HOWEVER; OFTEN I OBSERVE A DISPARITY; SUCH AS I DESCRIBE HERE. WHEN I SWITCHED TO QWO; ACR X MODE C ALT AND BEACON RETURN WERE DISPLAYED JUST FINE. UPON SWITCHING BACK TO OUR ASR-9; THE ACFT WAS A 'SKIN PAINT' TARGET ONLY. FOR THE NEXT 40 MI OR SO; I NOTED THAT ACFT X XPONDER APPEARED TO WORK VERY INTERMITTENTLY WHEN USING OUR ASR-9; YET EVERY TIME I OBSERVED IT USING QWO; THE XPONDER REPLY APPEARED ROCK SOLID. BACK IN THE MID 90'S; WHEN WE FIRST SWITCHED TO MODE S; WE EXPERIENCED THIS PROB WITH A HIGH PERCENTAGE OF GA ACFT.