PU-23 PsNee modchip installation diagram

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 PsNee modchips in my store.

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

PU-23 PsNee modchip installation diagram

PsNee ATtiny45 pinout

Arduino pinout:

  • Pin VCC - VCC
  • Pin GND - GND
  • Pin 3 - Debug TX
  • Pin 4 - BIOS A18
  • Pin 5 - BIOS D2
  • Pin 6 - SQCK
  • Pin 7 - SUBQ
  • Pin 8 - DATA
  • Pin 9 - GATE_WFCK

PU-23 PsNee installation diagram

PU-23 PsNee installation diagram, alternative points

Above are some diagrams for installing the PsNee into a PU-23. The first diagram shows the pinout of the ATtiny45, the second shows the installation diagram (including pin numbers for Arduino users), and the third shows some alternative points. Click on an image to open it in a new tab where you can zoom in to get more detail.

Let me know if any of the points aren't clear, I can clarify them for you.

Installation tips

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.
  • You don't need to connect pins one and two of the ATtinyX5 chip. Just desolder the wire.
  • Use a multimeter to probe around for alternative VCC and GND points closer to where you position your chip for a cleaner installation.
  • For DATA, be careful not to bridge the connection to the other resistor next to the one you are soldering to.
  • Don't apply too much solder to SQCK, or you'll bridge the pins on the chip.
  • For the wires that go into the holes, or vias, of the board: it's easiest to stick a small 30 AWG wire through the hole, then heat the wire and hole while adding solder.
  • Placing the chip on top of the chip above SUBQ and SQCK is a good spot.

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.

  1. William Quade (me)

PU-23 PsNee example installation

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January 19, 2019 9:56 PM

I hope it helps someone:
If you want to use an arduino nano, you have to erase the bootloader. To erase the bootloader you have to write the code with an isp if not it is not going to work.
i'm leaving on this link some pics of te instalation i made
link: https://mega.nz/#F!DGIygCbD!hTUX5TXdciOeCU9eNkX5hw

May 11, 2019 5:32 PM

Elsalas55 thank you!

June 8, 2019 4:32 AM

I accidentaly remove the resistor on data connection... anybody knows the value for him?

July 10, 2019 11:16 AM

Do you have any idea why can't read my scph-9002 any NTSC game? It just stuck on the second screen. My another scph-7502 with psnee plays any of these disks. And It can't be nor laser or disk problem because it is reading easily crappy audio discs and I played some PAL games on it without any problem. I've used the same psnee code on both of them with an arduino mini.
Thank you for any advance!

July 22, 2019 6:17 AM
Reply to  William Quade

I'd done checking, and It didn't change on anything, but at least I did an acceptable job first time. I think the problem is the laser. I don't have oscilloscope to adjust the laser. I think it is also pointless because after 55xx series the laser can adjust it self if I'm not wrong. I could be wrong but I can't explain why it can't read some games from the same type of medium quality verbatim disc. It can't read any low quality maxell only recognize it audio disc. Some game (RE I (original us version), Medievil I (us)) disc… Read more »

July 26, 2019 7:42 PM

Heres a pic of my install

December 2, 2019 10:23 PM


Just wanted to say thanks for the excellent documentation. PsNee'd my own ATtiny85 and installed using this guide and magnet wire. Worked first attempt on PU-23 board.


March 10, 2020 3:17 PM

Thanks; worked fine for me. Photos of the installation here: http://thp.io/2020/psnee.html

April 21, 2020 10:07 AM

Excellent work on the guide. I've got a PU-23 board which I'm trying to mod, but the GATE_WFCK pad is missing, are there any alternatives, apart from the leg of the IC?

July 29, 2020 9:29 PM

I'm having some confusion about the images above. On the first image indicating solder points, VCC and GND are at the bottom of the board. On the subsequent image of the finished install, the VCC and GND appear to be soldered directly under the chip location. Please clarify.

August 28, 2020 7:21 PM

For board 9001 is there a alternate data (yellow) solder point? I am traumatized with them small ass resistors. 😀

Daniel Lepore
Daniel Lepore
September 22, 2020 7:09 PM

Hi, I'm using an Arduino uno and I beilive i"m doing everything correctly and cant get it to work, ive tried every version of psnee i could find and no dice. Any tips?