This is a controller keyboard specifically for the Yamaha CX5M Music Computer. It is in mint working condition, and complete with its original packaging. Here's a quick description...
 
Yamaha YK‑10 Music Keyboard
The Yamaha YK‑10 is a dedicated music keyboard controller designed for Yamaha’s CX‑series music computer systems and FM sound modules. Released in 1984, it was created to provide an intuitive, piano‑style playing interface for Yamaha’s pioneering FM synthesis platforms, including the SFG‑01 and SFG‑05 FM Sound Synthesizer Units. 
Purpose‑Built FM Controller: Developed specifically for use with Yamaha CX‑series MSX music computers, the YK‑10 allows direct performance control of Yamaha’s early FM synthesis engines. 
Full‑Size Keyboard Layout: Features approximately four octaves of full‑sized keys, providing a comfortable playing experience for melodic and harmonic input when composing or performing. 
Proprietary Direct Connection: Connects via Yamaha’s 20‑pin IDC connector, designed to interface directly with compatible FM sound synthesiser units without the need for MIDI. 
Designed for FM Programming & Composition: Commonly paired with Yamaha music software cartridges, the YK‑10 was widely used for FM sound creation, sequencing, and performance control within the CX5M music computer system. 
Robust Vintage Construction: Built in Japan with a lightweight but solid chassis, the YK‑10 reflects Yamaha’s durable 1980s hardware design ethos.
Highly Collectable Peripheral: Now a sought‑after accessory for completing original Yamaha CX‑series setups, the YK‑10 is valued by collectors, FM synthesis enthusiasts, and vintage computing fans. 
 
The Yamaha YK‑10 represents an important piece of Yamaha’s early digital music ecosystem, offering hands‑on performance control during the formative years of computer‑based music production.