Sega Master System Dual bios mod help

[bust3dstr8]

I'm looking to install a dual region bios so I can play SG1000 and Japanese titles in my SMS Model One.

Problem is...I'm just not sure which of the three 28pin NEC chips is the bios on this model.

I think it's the one right next to the 6264 ram, but I want to be sure before removing it.

Can anyone confirm the location on this model SMS?

[ApolloBoy]

It's usually marked with a Sega part number, usually starting with "MPR-xxxx" or something like that.

[FABombjoy]

If you have the -6067 board, it's the CXK3864

If you have the -6629 board, it'll be MPR-something

On both PCBs, the 4 pads for connecting A14 are right next to the BIOS (circled and marked 128 and 64)

[bust3dstr8]

Derp....I thought the CXK3864 was a 8K*8 RAM because of the part#

Thanks FABombjoy

[FABombjoy]

Yeah, it threw me the first time, too. I assumed it was some kind of Sony-brand RAM as I didn't know they made mask ROMs

If you're burning a dual BIOS, be sure to get the proper version for the -6067 (v1.3), if indeed that is the PCB revision you're working with. The init routines were changed in later BIOS revisions and they aren't compatible with the -6067 hardware. I've tried v2.4 and v3.4 and they both crash on startup. This was using desoldered OEM BIOS chips.

[bust3dstr8]

Looking good so far...I am trying out a few different bios with a flash chip.