If you are using the fully populated cable, it is possible that a the cable has a problem.
If not it could be the port defective, I had one like that I had to switch over to the operator panel Connector instead of the Main Board connector to get it working, you really need a RS232 break out box to trouble shoot the port.
I have a Fanuc 10 RS232 manual if you need send me an P.M. with email add.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.