2004 Haas minimill RS232 question

As the title says I have Haas mill. I have been learning how to use it, and came across a small problem with what I believe to be with the circuit board on the top RS232 connection. The machine has two rs232 ports. The issue was with trying to send a program back to the computer, it works just fine from computer to machine. I switched the top cable to the bottom port and machine will now send back to computer. Being anal like I am I would like the top port to work so I can put it back to normal. A friend suggested that the top board may have taken a voltage spike and fried part of that board. I found some NOS boards on ebay but not sure of the part number, or if they will work on my machine. Anybody have a parts manual for one of theses machines so I can get a part number?
Mike