The long opto runs the width of the machine nearly down the middle where the green mist is on the PF. The right side is the white transmitter. The left side is the black receiver. Make sure those two are in perfect alignment. Take the mist ball out while in switch test mode and swipe your hand through the invisible opto beam. You should hear the game detect your hand as if it was a ball and go "beep", triggering the long opto.