Yamaha YIS-303
This page was last modified 16:23, 16 December 2021 by Mars2000you. Based on work by Gdx and Rderooy and others.



The Yamaha YIS-303 computer is a bridled CX5 with a different color.

This model was sold without any module, the printer port and half of the RAM are missing, the access to the expansion bus slot is blocked.

It was aimed at the Japanese market and features a simple Japanese keyboard with 70 keys. The power supply is internal. Two keyboard overlays were provided, one is gray, the other one is black.

Brand Yamaha
Model YIS-303
Year 1983-11
Region Japan
Launch price ¥49,800
RAM 16kB (in slot 0)
Media MSX cartridges, side slot modules
Video Texas Instruments TMS9918A
Audio PSG (YM2149)
Chipset Yamaha YM5214
Keyboard layout QWERTY/JP50on
Emulation ROM dump needed. See this thread for details


Yamaha YIS-303 box + content
Yamaha YIS-303
Yamaha YIS-303 underside
Yamaha YIS-303 label
Yamaha YIS-303 box
Yamaha YIS-303/503 manuals
Yamaha YIS-303 left side
Yamaha YIS-303 right side
Yamaha YIS-303 back
Yamaha YIS-303 keyboard overlay
Yamaha YIS-303 PCB
Yamaha YIS-303 missing printer port
Yamaha YIS-303 PCB with RAM extended to 32kB + printer port added


The YIS-303 is a MSX1 with a Z80A from Sharp (LH-0080A). It supports all Yamaha modules, except the module HC-A602S from Victor, because the Video processor is not a TMS9928A.

To use the expansion bus as second cartridge slot, you need the Yamaha Single Cartridge Adapter CA-01.

The printer port is missing but we can add it by soldering a connector and the four chips near the cartridge connector on PCB.

We can also add 16KB RAM by soldering 4416 x2 and two 74LS244 instead the straps in the chip locations near at right. However, it is better to use a cartridge memory expansion (64kB or a MSX1 compatible memory mapper) to improve the compatibility. This prevents the main RAM from being split into two slots at address 8000h.

Slot Map

Slot 0 Slot 1 Slot 2 Slot 3
Page C000h~FFFFh RAM Cartridge
Page 8000h~BFFFh
Page 4000h~7FFFh Main-ROM
Page 0000h~3FFFh