Danny,

In 1981-83 there were only a few Yamaha portable arrangers, and, of course, they were based somewhat on bits of the Electone Technology.

1981: PS-10, PS-20, PS-30.

1982: PS-30B, PS-3(I), PC-100, PSS-30, MP-1 (had a music score printer built in), PS-300.

1983: PC-50, PS-35, PS-35S, PS-55 (PCM drums), PS-55S, PC-1000, MK-100

The PS-6100 came out in 1984, and was pretty cool for the day. It used the current at the time FM synthesis to make the preset sounds and also, like the earlier PS-55, had PCM drums.

The PSR-500 didn't come out till 1991, and the PSR-410/510 in 1993.

Quite a few of the earlier Yamaha and Casio keyboards became popular with the "circuit bent" crowd, and were modified in all kinds of cool (and strange) ways.

What we play today is pretty amazing, considering their origins.

Ian