I was able to put together a cheap PS/2-to-MSX mouse interface using an Arduino Nano. The project works by using the Arduino Nano as the bridge between a standard PS/2 mouse and the MSX mouse port.

The design is based on denjhang’s MSX Nano Mouse 2025 repository, which provides both the Gerber files for the PCB and the firmware source code. Having those files available made the build straightforward and inexpensive: I could order the board, assemble the small set of components, flash the Nano, and connect a PS/2 mouse.

After some initial setbacks, we are finally making progress with the Omega MSX.

The first problem was a defective Yamaha 8139 chip, which prevented the system from booting at all. Once that was resolved, we were able to get the machine to display C-BIOS and its diagnostic screens.

That revealed a second fault: capacitor C64 was measuring only 68 µF, rather than its specified 220 µF. This was responsible for a strange yellow ghosting effect on the display.