Although mine was a toy (a Casio SK-1) that I got in elementary school. It did have a full modeling synth feature built into it.
It was almost as bad a moving patch cables. You would enable the synth mode, and it would play a pure sine tone. Then you could use the first several keys to select the waveform you wished to use. The usual suspects were available, square, sine, triangle, sawtooth. Then the upper keys would pick the frequency of that component. Up to 4 waveforms could be combined. There was an envelope select button so you could modify the different parts of the ADSR. Then you'd press the Synth button again and could play your newly created "patch". When you turned keyboard off, you'd lose the work.
