Can't reduce the field size with the table in the horizontal position

Ultranet: Can't reduce the field size with the table in the horizontal position See long description. With the table in the hoirzontal position the collimator will auto collimate properly. If you try to reduce the size the lateral blades will not stay in the reduced position and when it resets to the auto mode, the long blades will also reset. With the table in the vertical position the collimator works normally. The FE replaced the RF Positioner I/O, the collimator servo boards, and the collimator. It works normally to the wall bucky. Also, check the SID pot, for noise and no dead spots. And check the feedback pots from the collimator and the cassette tray, in the vertical and horizontal positions.