The last version of the original PlayStation 1 design was the SCPH-900x. Most of these consoles have PU-23 boards inside. The most notable difference between the 9000 series and earlier consoles is that Sony removed the parallel IO port on the back. They also shrunk down the size of the board significantly.

For more information about MM3 chips click here, for more information about PS1 modchips click here.

PU-23 MM3 modchip installation diagram

Above is the diagram for the PU-23. Pin four is located towards the top left side of the board.

Since the diagram isn’t the clearest I’d like to mention that the second pin connects to the top most pin on the left row of pins on the chip. Pin three connects to the left contact on the middle resistor, and pin six connects to the top contact on the left capacitor.

Installation tips

Here are some tips I have for you when you are soldering your chip into the PU-23.

• You don’t need to connect pins four and two.
• Pin 3, and 6 can be tricky. Don’t push on the components with your soldering iron or they might get knocked off the board. You can use tweezers to carefully solder them back on one side at a time, the orientation doesn’t matter.
• Make sure the wire on pin 3 and 6 don’t come into contact with both sides of the component (this is especially common if you run the wire directly on top of the component).
• Don’t apply too much solder to pin 2 or you’ll bridge the pins on the chip.
• Placing the chip where the pin two circle is, or below it, seems to be the ideal location for placing the chip.

Diagram success rate

Here’s a list of people who have successfully modded their console with this diagram. Leave a comment and I’ll add you to the list.

1. William Quade (me) (I’ve used this diagram many times and haven’t had any problems with it)

Example installations

This section has photos of some successful installations which you can use to get a better understanding of how everything is wired and positioned.

Here are some installations I’ve done on some SCPH-9001’s:

This first image shows a cleaner way to install the chip with six wires. I probed the board with a multimeter to find alternate points to solder the wires to that are much closer together. I use the capacitor to the right to get the VCC and GND (pins 1 and 8) connected to the chip with really short wires.

Below  are a couple of messier 8 wire installs I did using points on the diagram This installation works, but the wires are much longer than they really need to be.