I recently got a SK-60, I hear I am lucky, since they are rare in the USA!
The sound quality is wonderful, but as others have said here, the only reliable bends seem to deal with
the sampling functions only, but power supply mess should do something!
Luckily, it uses an external ram; 1 pin is clearly R/W select, all the others are data lines!!
If you slow the clock speed down, you can get longer sampling times than 6 seconds, but it sounds crap, in a good way
I was able to get at least 20 seconds out of it this way, and the lower clock makes the KB sound cooler!!
Will post sounds when I have time...