Gator,
Glad to hear you have what you need. I'm of the same thought as Len and SEC. Check the teeth in the wheel of the DDD (distance direction detector). If the light from your emitting diode does not reach the photo transistor your pulse is lost. It will more then likely show as a large gap in the count comparison of AVP16 and POS16. Just a heads up there is an 18v battery backup on the DDD board.