The request for this mod was to stack another BIOS on top the existing BIOS on a SEGA Dreamcast, and add a physical switch to enable either of both BIOSes to boot from. The instructions for this mod can be found in the Wayback Machine as the website no longer exists. The instructions cover both VA0 consoles and VA1 – VA2.1 motherboards. The console I was sent was a VA1, and already had an HDMI mod installed, a PicoPSU and a Noctua fan mod too.
The customer provided a new flash chip from RetroSix. On disassembly, it was clear that the BIOS had already been changed, which meant that the instructions in the website didn’t quite work anymore as they assumed a stock BIOS which doesn’t require extra wiring (namely, they stock BIOS doesn’t have a RESET pin, but the newer BIOS has a RESET pin that need to be connected to Pin 23 to enable the chip from working). I decided to attempt the mod anyway, looking at chip pinout diagrams and
Stacking the second BIOS was relatively tricky because the pin legs wouldn’t touch, so bridging the pins with solder wasn’t easy and I had to do without flux and test the connection. I also added a ON-ON switch, meaning it has two positions that enable either pair of pins to be bridged.
Unfortunately I could never the console to boot with the switch in either position. I tried to vary the design, connecting the RESET pin separately, but nothing worked. So I had to abandon the mod and put everything back as it was.
I did however had a change to clean and retrobright the console. The bottom part was particularly yellowed
First I had to completely disassemble and wash the shell. The I put it around 12 hours in the retrobrigthing chamber and it came out perfectly white.
Note how the modem couldn’t be retrobrighted in this occasion as the shell is difficult to disassemble. I also printed a new support for the Noctua fan as the one that was in there came broken
