Yep, it started on Tyros2 ...follow link below, and click on Specs.http://usa.yamaha.com/products/musical-i...os2/?mode=model
It 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.