I need to track down a few of these Yamaha CS series synths. I’ve always been interested in the CS-01 and way back when I was in Junior High, I took a music class where they had a CS-15 and a blue faced ARP 2600 in a backroom somewhere. I used to call the ARP a “scoreboard” since I had no clue what it was back then. The music teacher didn’t know how to use it and it was missing the controller keyboard, but I had tons of fun messing around on the CS-15. From what I recall, they were in brand new condition and the best I can figure is that they were donated by a music store that closed or something as a tax write off.