Yamaha CS80

>> 1)Suboscillator does not work: no matter what waveform selected, there
>> is no modulation on either VCO, VCF or VCA. Speed does not do
>> anything. As a consequence the corresponding aftertouch features do
>> not work either.  Routing Noise to the parameters mentioned above does
>> result in (some) effect. Any ideas?
>
>Bad VCO chip?  Looks like IC5 on the SUB board:
http://d.yimg.com/kq/groups/13287191/or/1278022767   

That's my guess also. 

JH.