Allen-Bradley 2705-K11C1 fault and comm problem

[Bufordo 0]

Allen-Bradley 2705-K11C1 fault and comm problemHello, I have a machine that has a AB 2705-K11C1 keypad Redipanel connected to a 1771-SN scanner board. Installed on a PLC-2/02 (1772-LZ D). Problem started with a serial comm led blinking on the scanner board. The keypad display indicated no message. Green Led was on and red fault light was off. After checking continuity and also substituting another pair of wires between the keypad and the scanner board, we now have a red fault light on keypad and no serial comm led on at all. No fault led on scanner board.Backplane led on steady. The 150 ohm resistor is in place. We have substituted another keypad and scanner board and had same blinking ser. comm green led issue. Any thoughts on this ?