PlayStation 1: Done bios swap and modchip

Vendest

Krauser's Shoe Shiner
Joined
Jun 23, 2016
Posts
240
I'd like to share about an interesting mod for the PS1 which consist of replacing the bios and installing a modchip.
My PS1 is plagued with a native JPN bios which does not allow region mod thru modchip.
Documentation seems scarce even on PS1 dedicated forum however it was good enough to get me started.

1. Removed the OEM bios entirely although the bios can be disabled by desoldering /OE and /CE
2. Hardwired a socket for PLCC32 with wires long enough for the chip to sit in a convenient and accessible location
The PLCC follows almost the same pinout as OEM bios
/WE is unused and must be kept high with pull up resistor (10kohm)
3. Burnt a SST39VF040 with US region bios (AM29LV040B is also suitable)
4. Burnt a PIC chip with Mayumi v4 (JP) code

And here we go, the PS1 can load disc from any region and I finally got to try some real game play of RE1.5.

Nothing fancy nor too complicated but that did the trick for me.

https://imgur.com/a/qfKbR1q
 

GohanX

Horrible Goose
20 Year Member
Joined
Sep 28, 2001
Posts
12,490
Man, that's a whole lot of tiny wires to solder for that bios, you must have steadier hands than me! Good job getting it working, a chipped PS1 is a neat thing to have.
 

JoeAwesome

I survived Secret Santa, It wasn't Easy.,
Joined
Feb 19, 2016
Posts
3,116
I'd like to share about an interesting mod for the PS1 which consist of replacing the bios and installing a modchip.
My PS1 is plagued with a native JPN bios which does not allow region mod thru modchip.
Documentation seems scarce even on PS1 dedicated forum however it was good enough to get me started.

1. Removed the OEM bios entirely although the bios can be disabled by desoldering /OE and /CE
2. Hardwired a socket for PLCC32 with wires long enough for the chip to sit in a convenient and accessible location
The PLCC follows almost the same pinout as OEM bios
/WE is unused and must be kept high with pull up resistor (10kohm)
3. Burnt a SST39VF040 with US region bios (AM29LV040B is also suitable)
4. Burnt a PIC chip with Mayumi v4 (JP) code

And here we go, the PS1 can load disc from any region and I finally got to try some real game play of RE1.5.

Nothing fancy nor too complicated but that did the trick for me.

https://imgur.com/a/qfKbR1q

I just played around with RE 1.5 two weeks ago! Froze on me a ton, but it's possible to warp out on some occasions.
 

SpamYouToDeath

I asked for a, Custom Rank and, Learned My Lesson.
15 Year Member
Joined
Oct 3, 2005
Posts
6,059
The PS1 shadows the BIOS in RAM, right? (I think I've read about games patching it on startup.) If so, you could probably accomplish this with a cartridge on the parallel port too. It could just stomp the entire BIOS with a new one when it boots.
 

Vendest

Krauser's Shoe Shiner
Joined
Jun 23, 2016
Posts
240
Man, that's a whole lot of tiny wires to solder for that bios, you must have steadier hands than me! Good job getting it working, a chipped PS1 is a neat thing to have.

Thanks man, I didn't take close up pictures because the soldering is not that clean but overall I'm happy with it.

I just played around with RE 1.5 two weeks ago! Froze on me a ton, but it's possible to warp out on some occasions.

Did you use the latest patch? It didn't freeze although the game is obviously having a lot of issues with pre rendered textures and collisions.
Walking thru dining table or other obstacles, saw zombies across the walls...

The PS1 shadows the BIOS in RAM, right? (I think I've read about games patching it on startup.) If so, you could probably accomplish this with a cartridge on the parallel port too. It could just stomp the entire BIOS with a new one when it boots.

Thanks for the tip I didn't know that however I can now change the bios anytime without getting a gameshark for the I/O parallel port.
 

JoeAwesome

I survived Secret Santa, It wasn't Easy.,
Joined
Feb 19, 2016
Posts
3,116
Did you use the latest patch? It didn't freeze although the game is obviously having a lot of issues with pre rendered textures and collisions.
Walking thru dining table or other obstacles, saw zombies across the walls...

I doubt it. I think the image was from 5 years ago. No one walking through objects, but in some rooms, movement was at a snail's pace.
 
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