Build a PlayStation 2 Serial Cable

This page has instructions for building your own serial cable that connects directly to the PS2's EE processor. It only needs 5 wires soldered onto the PS2 mainboard, and a simple interface circuit to convert the EE's voltage levels to the standard RS232 levels.

Because there are at least 10 major PS2 mainboard revsions, and I built my cable on a V4, there might a few differences in the location of the points you'll need to solder. The main one is the pad for +3.3V. Refer to the installation diagrams of any recent modchip (Messiah, DMS, whatever) for your PS2 version, and you should be able to find the right +3.3V pad to use. Also, my pictures of the serial pads beneath the EE might differ slightly from what you see on your mainboard. As far as I know, the serial port pads exist on all PS2s, so as long as you find the right set of pads you should be fine. 

I used the following color scheme for the wires on the PS2 mainboard and the interface circuit: 

Red - +3.3V 
Black - GND 
White - EE core voltage (Vcore) 
Blue - EE_TXD / PC_TXD 
Green - EE_RXD / PC_RXD 
First, open your PS2 and get to the mainboard. Again, use the installation instructions of a modchip to figure out how to take apart your PS2. You should be facing the side of the mainboard opposite the EE, with the A/V and optical connectors closest to you. 

Start by connecting GND, then locate your board's pad for +3.3V and connect it.

If you look at the right side of the bottom of the EE, you should see 4 square-shaped pads. You should also see a gap between the first pad and the bottom three. This is the EE's serial port. The top pad is EE_TXD. Make note of the via (the tiny circle) sitting by itself immediately above EE_TXD. That's the EE_RXD pin. The third and fourth pads are RTS and CTS, but we won't be using those for our cable.