First try turning power to the No. 40 OFF, disconnect then reconnect the existing comms cable between the No. 40 Audio and Video processors, and power the No. 40 ON. If this does not help try a different comms cable, this is a straight through 4 conductor cable with a 4 pin connector on each end. If replacing this cable does not help contact one of our authorized service centers for repair assistance – their contact information is under the SUPPORT tab on the Mark Levinson website.