The project of upgrading Yamaha YIS805 to MSX2+ has been started. The upgrade will be reversible. So far it looks like that:
Gotek works way better than the real floppy. The computer now has 256kb of RAM and special jumpers to control the amount. The CPU and BIOSes have been moved to sockets. Next to do - upgrade VDP and BIOSes.
The model of the slot cover is here: https://www.thingiverse.com/thing:3816802
Using it since a year. Wonderful thing!
The machine now works in MSX2+ mode. I've found the way to install BIOSes and Subrom without any changes to the board and the chips. Next is the VDP change and FMPAC+F4 installation.
The upgrade is almost complete. The v9958 chip has been installed and the sync circuit has been updated to match the one on YIS503. The machine is being correctly identified by the software as MSX2+ with 256kb of RAM, v9958 VDP and FMPAC (which is physically not there yet):
There are some minor issues. The vertical scrolling is not as smooth as it could be, we will see what could be done to fix this.
Next phase - the creation of the special adapter board to install the RBSC's internal FMPAC+F4 combo board as well as the assembling of the board itself.
Here's the archive with all files that are needed for the upgrade. The files from 1.rom to 5.rom are ready to be put into W27c512 EEPROM. The numbering starts from the chip closest to the front panel. The jumpers J303 and J304 need to be soldered to configure the FMPAC BIOS. The 1N4148 diode at D301 is necessary to expand the slot 0 for FMPAC.
The adapter board for F4/FMPAC installation into YIS805 is ready and has been sent to the factory.
Instead of F4/FMPAC this board can also host the 2mb memory mapper board created by Andrey Koryakin. So this adapter board is usable in the original YIS805 as well as in the upgraded to MSX2+ version. You just need to install the socket for Z80 and you all set. The subslot for the mapper may be chosen between 3.0 (instead of Painter in Russian MSX) or from a few subslots in the expanded slot 0 for the original Japanese versions of this computer.
The F4/FMPAC for upgrade is ready. I didn't install the BIOS chip because it's already installed into the empty socket on the motherboard. Now I just need to wait for the adapter boards from China and I can do the final assembly.
I still have a few bare boards for sale, so please contact me if you are interested. This board is also suitable for Yamaha YIS503 and CX5MII computers.
We are currently designing the new video board for Yamaha YIS805 and similar computers. This board will have color composite video as well as S-Video (that is as good as RGB quality-wise). The new board will have the option to get the 3.58MHz directly from the main board, without the need for the special clock generator for NTSC. So far it looks like that:
The adapter boards for FMPAC installation have arrived. Those adapters will be installed on the special 3d-printed holders, that would be glued to the motherboard with a 2-sided tape and secured with screws or 3d-printed pins. I plan to install the adapter during the weekend.
