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 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.
- 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.
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.
- 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 images show 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 bottom to get the VCC and GND (pins 1 and 8) connected to the chip with really short wires.
Successfully completed. Hardest part is of course not bridging the pins on the IC. I did bridge the first two pins, and used a piece of solder wick with a chisel tip iron and a bit of fresh solder [on the iron] to pull the bridge from the pins. Be sure to check with a multimeter after removing the bridge to be sure you got it all. IIRC, there was in the megaohms of resistance on those first two pins. Also, use your meter to check the pins on the PIC 12C508 after installation to ensure no pins are shorted.… Read more »
Hi William, I cant thank you enough for all the work you did here on your site, I do appreciate it. I had the choice of modding my original 1001 or a 9001 which I know to be a little tougher so not wanting to touch my baby (the 9001) I went for it on the 9001 and it booted up first time no problems thats to you awesome and straight to the point diagrams. Cheers mate!! Curtz – I think I may have purchased the chip from you as well, any recommendations for a similar chip that will allow… Read more »
You can actually directly boot game backup discs on the Dreamcast, no need for a chip.
There are also mods for the Dreamcast that allow you to boot game backups over something like an SD or CF card.
William,
I recently purchased and installed a chip for my 9001. After installation, when I put in a disk it tries to spin for around two seconds and then stops, remaining on the main menu page. It isn’t the drive motor or laser as I have already tried putting in a different optical lens/laser drive assembly. I was curious if you had any ideas as to what could be the issue.
Thanks
It could be that the laser is worn out, or it could be a bad installation (if the wires are too long, or run over noisy components they can pick up noise and make the system have problems booting). Send me a picture of your installation and I’ll let you know if that’s the problem.
Thanks for the prompt reply! So I took out the modchip and it still won’t read audio CD-Rs. I just put a new laser and drive motor assembly because I also thought that could be the problem. The drive spins the disk twice like it is attempting to read it but then gives up. If you have any insight on why the unit won’t read audio CDs even without the chip installed let me know!
Can it still play genuine copies of games? If it can’t play audio CDs then that would mean that the laser is worn, and would be the reason why backups don’t work.
Hi William,
I’m having problems with my instillation. I’ve tried the discs on other systems and they play perfectly and official PS discs play fine after the install. I don’t see anything bridged, Can I send you pics somewhere and maybe you can tell what I have done wrong?
You can send me an email: liam@quade.co
I just installed a 12C508A into a model 9001 / PU-23 and I tripple checked my wiring which seems good and followed this “dummy proof” guide. However, when the PlayStation powers on, the cd drive keeps spinning. Disc or no disc it just jeeps spinning… so the question. what Did I do wrong???
Thanks
Could you post some links to pictures or your installation, or email them to me: liam@quade.co
Just wanted to say thanks I bought youre chip off eBay and installed it using this guide and it worked fine first go and this was my first big solder job. Just had to practice soldering to the small surface mount parts on an old non working psone. Great job with everything keep up the good work
What is the point of connecting pin 2 in the images if you go on to say that you don’t have to connect pin 2?
It’s an optional pin. It’s just in the original diagram to be complete.
Thanks for this guide, it works with my scph9002. One question for you: why we don’t need to connect pins four and two? What are they for? I have soldered pin4, but pin2 is very hard…
Pin 2 is for the clock line, and is only used for Mayumi chips. Pin 4 is used for the mode selection using the reset button, but isn’t needed because the MM3 supports every game already (some older chips had a disable mode so that games that had anti-modchip code could be played).
Hi William, I have a model scph-9001 console with a PU-23 motherboard. My original laser assembly was broken and i replaced it with a model scph-5501 laser assembly. Would the MM3 work with this installation diagram? Thank you.
Yes, because you still have the PU-23 main board from the SCPH-9001.
Thank you very much.
Installed yesterday, just needed a reminder on where pins 5-8 on the MM3 PIC were. Thanks.
Installed it in my 9001 and it works great. Also the can you explain if pin 2 and 4 hurts to have them hooked up?
Pin 2 for the MM3 does nothing. Leaving it connected likely won’t cause any problems.
Pin 4 is used to switch between operating modes using the reset button, so leaving it connected is not a problem.
Hi william, i’ve just install the mm3 modchip now, i’ve much experience in soldering, i Made a good clean job. But there si 2 strange things that i’ve ti notice, i hope you can help me: 1) i burn Moto Racer 2 EUR with cue file, the playstation read the disc like a music disc, start the media player software and not the game, i used imgBURN at 10x becouse the disc minimum speed is 10x… 2) i tre ti play ah original disc, it load, but sems that the down button is ever pressed and i can’t do nothing… Read more »
Elder Bog,
Not to jump in place of William. Try cutting your wires shorter.
Thanks for your efforts mate 🙂 Good resource. I just installed an mm3 in an Australian PAL 9002 unit. It would not work without pin 4 being connected though. Didn’t need pin 2.
man i love you easy install with your picture much appreciated works flawlessly
Successfully assembled! The schedule works fine but i would appreciate a better image quality. There should also be a ~100 nF capacitor between the power pins on the PIC.
Hello, long time ago i had a PS1 with PU-18 and 12C508A modchip, but it stopped working at one point through the years. I had bought me a year ago another ps1 with pu-23 but it did not had a modchip. I have tried now to transfer the modship in the new ps1 with pu-23 with the help of the diagrams on the webpage here, unfortunately now it does’nt play anything at all anymore? it always transfers directly to the main menu. i’ve checked the wiring couple of times but can not find any fault in it. Checked with a… Read more »
Are you sure the chip is an MM3? There were a lot of modchips that can use the 12C508A.
I don’t know much about it i’m afraid, this picture shows the chip as it was installed in the first PS1 (and always worked very well till the laser was worn out)
https://ibb.co/qN3ccFY
Yeah, that’s definitely not a MM3. It’s a classic 4 wire chip. You might be better off just getting a new modchip (the older chips don’t support anti-modchip games). Here’s a 4 wire diagram I have for the PU-23:
Thanks for the information. i have tried it with the new wire diagram, but no luck, same result.
Also removed the chip completely again, and also same result, doesn’t play any disc anymore now, so i messed it up probably.
But thanks again for the information and your help.