Ps1 scph 1000 replacement bios

[cinderglacius]

Hello friends, I'm from Mexico.
I currently have my ps1 mod scph 9001 and it works great. But I have always wanted a ps1 model scph 1000, I am about to buy one but I know that the bios will be Japanese and if I want to play with u / c games I must replace the bios. Here in Mexico the scph 1001 model went on sale but it is extremely expensive and that is why I turn to a Japanese one. I know that this model uses PU-7 or PU-8 pcb and both have 40 pin bios.
What would be the replacement ic for this model? or is there definitely no replacement?
Thanks and excellent forum.

[TriMesh]

The mask ROMs in these old machines use a standard JEDEC pinout - so the cleanest approach is to get a 3.3V 512kbit SO EPROM like a 27V400 and just solder it in - this is an exact pin for pin replacement and will just drop in place of the ROM.

These were however never very widely used parts in that package and now seem to be almost impossible to find.

Another approach is to use a 3.3V JEDEC complaint flash part in a 44 pin SO package - something like the Intel 28F400BL/BV (not the 5V only BX part) - and solder in in with pin 3 of the part lined up with pin 1 on the PCB and then tie pins 1, 43 and 44 on the part to VCC. This isn't as tidy or elegant, but the chips are much easier to find.

Also note that depending on how old the console you get is you may not need to do this at all - the early SCPH-1000s didn't have the Japan territory license check in the ROM (well, they did, but it was bugged - so all it did was suppress that black "licensed by" screen and then proceed to boot the game anyway).

[cinderglacius]

OK thank you very much.
Personally I would like a bios of the 7xxx or 9xxx series, I suppose it should work right?
For the programming on the chip I only have to download the bios in the .bin format and enter it like this without modifying any line?
Thank you very much again

[TriMesh]

OK thank you very much.
Personally I would like a bios of the 7xxx or 9xxx series, I suppose it should work right?
For the programming on the chip I only have to download the bios in the .bin format and enter it like this without modifying any line?
Thank you very much again

Yes, you should be able to just directly program the boot ROM image to the device without any changes. I can't say for sure if using a newer version of the boot ROM on an old board will work, but I can't see any reason it shouldn't.

[cinderglacius]

I can't find the 27v400.
I found the 27c400 and the pinout seems to be the same.
Could that work?

Thank you very much

[TriMesh]

Unfortunately not - at least not reliably. The difference is the supply voltage = 27C400 = 5V part, 27V400 = 3.3V part - and the PSX is a 3.3V system

Also note that full-size DIP package won't fit on the board - the package that fits the PCB is a .525" small outline type. If you want a part that will fit on the board rather than needing to be hardwired you will probably have much more luck looking for flash parts.

[cinderglacius]

I see.
I was looking and here in my country and I did not find the 28f400, I found the 29f400, according to the pinout is the same, can I use this or will I have to order a 28f400 from aliexpress?

[TriMesh]

I think the 29F400 is a 5V part - see if you can get a 29LV400, which is the 3V equivalent.

That pinout you posted seems to be for some other device - possibly a 29F800 since it has an A18 pin...