Yep, it started on Tyros2 ...follow link below, and click on Specs.
http://usa.yamaha.com/products/musical-i...os2/?mode=modelIt was initially designed specifically for the Tyros2's new SA Voices, although the Combo Division, at that time, also wanted (and got) it for their Motif line.
As far as I know, the first Tyros was not made in Japan (it was made in Indo-China, I believe), and the keyboard action, although pretty good (velocity and aftertouch), was not quite in the same league as the FSX design...the latter had a deeper throw, a tad more resistance, and improved aftertouch response.
Tyros2/3/4, were all made in Japan, and I expect that's where Tyros5 will be manufactured.
I asked why the original Tyros's keyboard wasn't kept and used in the higher end of the PSR line, but no one offered any reason, so it must have been a cost issue, probably to keep price competitive with other brands, but that's just a guess.
Ian