ROM replacement chip for SCPH-9002

[dikdom]

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]

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

[dikdom]

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)

[nocash]

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]

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)

[dikdom]

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