Do me favor and ohm out your working DB-9 to see if there are any shorts between any two pins that may not be service affecting. I picked up shorts on many of the max chips leads prior to doing any soldering and i didnt use flux yet, my bad but in my defense i was doing it on the dashboard of my truck on my lunch break, soldering iron plugged into 70W inverter :-)
On that schematic, i dont know where the lines go to once they leave the chip. Potential designed shorts on mobo?