SY22 problem/schematics

[Goddard, Duncan]

>>>He's got Yamaha SY22 recently but it has faulty key: H1 sends note
> on and velocity but no note off. Pressing some other key finishes
> it but not always the same key. Synth is otherwise in nice shape
> and no external abuse visible.<<<
> 
> 
sounds like keyboard contacts. I have the same symptoms with,
coincidentally, a p2000 sampler (another dave smith box). under each key
there are three contacts which the conductive rubber pad thing hits at
different times depending how fast the key goes down. I think the time
interval between making the first pair and then all three gives velocity
information, and note-off is generated when either/both of the note-on
contacts is disconnected from the "common" contact again. if the
disconnection of the three contacts happens in the wrong order (because the
pad is worn or something) then you don't get a note-off...... duff design.

(which got me thinking again about a more reliable, optical-based way of
deriving note-on/off, both with velocity, and aftertouch.... rather than a
simple solid vane moving between two opto-sensors, you could use something
with graded transparency..... I'd have to draw it really.)

on the other hand, it could be the keyboard controller ic. if it's the same
chip as in my p2000, then your friend is also in "chop it up and make a
rack-module out of it" territory as the I-626 chip is no longer available.
this is a bit unlikely. 
how does it behave with midi-in?


d.



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