I had an SY-77 lying around in my old house so I decided to take it appart just to look how it is built and what is made of. It wheighs around 15 kg and it is a very solid built. You have to unscrew at least 14 screws just to remove the underside panel which reveals the electronic guts of the instrument. There are two main boards visible. Both have countless DIP chips and some surface mount giants. Of course, it is well over me to make out what each of the chips actually do so I was just staring at them in awe.
The SY was the flagship of Yamaha back in the 90s. It had 32 voices, 16 of them where AFM (an advanced kind of DX's FM synthesis with more algorithms between the operators and the ability to feedback an operator with it's signal) and the other 16 were AWM (a PCM like sample playback synthesis method). Each voice signal could have two resonant filters and the output of the AWM voices could be used as input to an FM operator. This, if you didn't know what you were doing, was usually a noisy mess. I didn't but the guys that programmed the presets did because it has some wonderful mininoog style sounds that became very expressive with the velocity/channel aftertouch, semi weighted keyboard the SY features.
Moreover, in its FM synthesis, a different envelope (both pitch and amplitude) could be assigned to each of the FM operators so you could program some evolving sounds. Its envelopes featured repeat points and so on.
The SY also featured an on board sequencer which I didn't really like (It was the time of cubase on atari ST). But my SY grew older, some keys grew sticky, some sliders were in need of repair and it gave way to the VST stuff. The floppy drive died a horrible-sticky death (there is a rubber band that used to turn the disk but it just disintegrated in my hands leaving a sticky, tar-like residue. I cleaned it with acetone but I need to find a replacement now).
I put it back in its case, waiting for the time to move to a bigger house where it will take the place it deserves. A master controller maybe? Or maybe not?
For more pictures and closeups of the ICs you can always look here