Unplug ALL CORDS from this Board.
Power the system DOWN and then back up.
Take a KNOWN WORKING PHONE back to the control unit and test each port.
I suspect you will find that each port works ok.
NOW, One at a time, re-plugin the CORDS and test each phone.
I suspect you will find that one PHONE (OR WIRE TO THAT PHONE) will cause the board to fail.
When you figure out which phone/cord does that, then you will know who your "BAD BOY" is.
At least that's my theory......
-OR-
YOu simply have a bad board, but I doubt that....