I have the Allister 3000 and needed to replace the photo sensors across the garage door opening. They appear to work fine when the beam is broken. The wiring is to terminals B & C on the P4 board as per the wiring drawing, but the door will not close when the beam is not broken, just starts to close and re-opens.
I don't see a use for the A terminal on the P4 board. Prior to getting the new photo sensors I shorted A to B to be able to operate the door.
Any suggestions would be appreciated.