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.
I sell MM3 modchips in my store.
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 pin three connects to the left contact on the middle resistor, and pin six connects to the top contact on the left capacitor.
Here are some tips I have for you when you are soldering your chip into the PU-23.
- Cut your wires to be as short and direct as possible.
- Don't connect pin two of the chip to anything.
- Pin 4 can either be connected to the pin 4 location in the diagram, or pulled high by connecting it to pin 1 on the chip.
- 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).
- Placing the chip where the pin two circle is, or below it, seems to be the ideal location for placing the chip.
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 is an installation I have done on a PU-23 board. I used some alternative points for the power and ground connections (pins 1 and 8) for a cleaner installation. Pin 6 is also different but is connected to the same place.