:null:
Donate & Support PSXDEV.NET

We have been operating since 2012 providing users with a place for free information, free downloads & zero ads.

It has always been a safe and clean forum with no spam for other members interested in the PlayStation 1 to meet and make new friendships.
It's a place for those who are interested in learning about programming, reverse engineering and experimenting with hardware/software for the console.

We have never asked for donations before but it has reached the point where the server costs are becoming too much for us.
We would like to politely ask that if you use this site that you donate any amount you can to show your support to assist with the hosting fees in order to keep PSXDEV.NET alive.

Users who donate will be rewarded with a new profile rank on their account badge ;)
Just be sure to include your handle/alias when sending the donation or message me here with your BTC address.


Bitcoin: 1GqS7rr8jYPzT4Lp9Uua3D5thUH8ZnWyD8

Thank you for your contribution :praise
:null:

ROM replacement chip for SCPH-9002

Post a topic about yourself to let others know your skills, hobbies, etc.
Post Reply
dikdom
What is PSXDEV?
What is PSXDEV?
Posts: 4
Joined: Apr 07, 2023
PlayStation Model: SCPH-9002
Location: Hungary

ROM replacement chip for SCPH-9002

Post by dikdom » April 7th, 2023, 1:28 am

Hi,
I got two faulty consoles recently, none of them boots properly (one shows a simple black screen, the other one shows the first boot screen, but with garbled sound/noise and doesn't proceed from there).
I watched a ton of YT videos and read a few articles and I came to the conclusion that this second console probably has the 'faulty BIOS chip' syndrome. (I already reflowed the pins of IC102 - the BIOS ROM chip - no change).

So here are my questions:
- in theory if I replace the original BIOS ROM chip with another, working SCPH-9002 console's BIOS chip, should it work? I mean isn't there any serial number check, or something?
- In theory if I replace the original BIOS ROM chip with a substitute using a 3.3V, 8bit EEPROM/flash chip (and flash it with the original BIOS content), should it work?
- I checked the SST39LV040, PLCC32, that would be lovely, the downloaded ROM file could fit in the 512kB chip. But. According to the schematics of the console there are A0-A19 address lines of the chip, which means the console could address 1MB - not 512kB. Where is the rest of the BIOS file?

Last one:
- if I already 'reflashing' my PS1, is there a BIOS variant for my console that enables it to load backed up games? Or some extra mods always required for that? ...


Thanks in advance,
dd


I know there is such a replacement kit readily available, but that would cost more that these two consoles (+2 faulty slim PS2's...)

PhyChris
Interested PSXDEV User
Interested PSXDEV User
Posts: 7
Joined: Apr 12, 2015

Post by PhyChris » April 7th, 2023, 7:25 am

bad caps are also something to think about with hardware this old :)

dikdom
What is PSXDEV?
What is PSXDEV?
Posts: 4
Joined: Apr 07, 2023
PlayStation Model: SCPH-9002
Location: Hungary

Post by dikdom » April 20th, 2023, 8:09 pm

Okay,
first, I somehow mixed things up and write BIOS ROM chip instead of BOOT ROM chip. I meant BOOT ROM chip in the original post.
Secondly, I replaced the 220uF caps, no change on the half-booting PS1
Thirdly, I found a blown fuse in the blackscreen PS1 (it was on the 3.3V line), replaced, that PS1 is fixed. It boots properly, I could play with it.

So let me focus on the faulty PS1. I designed a small PCB for socketing a SST39LF040 flash EEPROM chip. That is a 512kB EEPROM while on the boot IC there are A0-A19 address lines, which makes 2^20 = 1MB capacity. The backed up boot rom images are 512kB. So that is confusing... I hope the A19 line is not used because I didn't use it either (not connected on my pcb).

What I plan to do is to
- remove BOOT ROM IC
- prepare and solder in my PCB
- solder in the SMD socket of the SST chip (unfortunately when the PLCC socket is soldered onto the PCB, it cannot be soldered to the motherboard... yeah, this is a tricky part)
- write the EEPROM with the 9002 (PAL) BOOT ROM content
- put everything in place
- hope the best

As a cherry on the pie I added some pads for the MM3 (12F629 smd) chip (power is connected, two wires less to be connected)

User avatar
nocash
Verified
PSX Aficionado
PSX Aficionado
Posts: 487
Joined: Nov 12, 2012
Contact:

Post by nocash » April 22nd, 2023, 9:13 am

The A19 line is don't care for 512Kbyte ROMs. For ROM replacements, I would solder a ribbon cable on top of the old ROM chip (and deactivate it's chipselect pin), and then install the put the FLASH/EPROM socket somewhere where you have enough space.

Going by your description, I am not too convinced that you have a broken ROM... Problems with SPU, RAM, or with one of the various power supply voltages might be more likely... The ROM contains 3 code sections: One kernel section executed in ROM, another kernel section relocated to RAM, and the Boot GUI section self-decompressed to RAM. And they are apparemtly all intact enough to display the <S> logo.

dikdom
What is PSXDEV?
What is PSXDEV?
Posts: 4
Joined: Apr 07, 2023
PlayStation Model: SCPH-9002
Location: Hungary

Post by dikdom » May 30th, 2023, 1:25 am

Thanks for the reply and sorry for not being too active lately.

This is what I did yesterday:
IMG_20230527_153521_HDR.jpg
IMG_20230527_164209_HDR.jpg
IMG_20230527_172530_HDR.jpg
IMG_20230527_191818_HDR.jpg
IMG_20230527_193812_HDR.jpg
IMG_20230527_194115.jpg
In the middle of the operation (before socket was soldered on red PCB) it turned out that D1 doesn't arrive to GPU, so I added a patch wire. Finished the operation, socket is checked, IC is burnt, test... black screen..

This morning I had an idea and I was right: some socket lines are shorted with the red PCB's side contacts - of course with wrong lines.
So tonight I have two options: redo everything and put back the original ROM (with patched D1 line) or resolder the socket with properly insulated PCB underneath...

(edit: the flash chip is SST39LF040 - 55ns. Or at least it should be 55ns, it arrived from Aliexpress)
You do not have the required permissions to view the files attached to this post.

dikdom
What is PSXDEV?
What is PSXDEV?
Posts: 4
Joined: Apr 07, 2023
PlayStation Model: SCPH-9002
Location: Hungary

Post by dikdom » May 30th, 2023, 6:12 pm

After an hour of struggling with the shorts I decided to put back the original ROM. Lo and behold, the PS1 is alive again: boots properly, starts game CDs. (only one pad was torn during removing my custom PCB...)
IMG_20230529_210716_HDR.jpg
IMG_20230529_212438_HDR.jpg
IMG_20230529_213148_HDR.jpg
I feel a bit sorry that finally my custom EEPROM solution didn't go that well as I expected (I didn't have any kepton tape at home)..
I thought I could fire it up using my flash chip and write programs and ... nah, I wouldn't write anything for PS1.

Anyway, thanks for the support!

dd
You do not have the required permissions to view the files attached to this post.

Post Reply

Who is online

Users browsing this forum: Google [Bot] and 1 guest