This is a glitch/random bend by Finlay Shakespeare http://www.futuresoundsystems.co.nr .
The mod was originally done on the casio sa1 but it should work with all the sa-serie.
Here is another random/glitch mod I found in a couple of forums:
Doing some circuit bending on my casio keyboards I collected some useful schematics to “safe-bend” the casio sa serie (sa 1 2 5 8 10 20 etc).
The main mod is the one from Casperelectronics that adds interesting bends as the “glitch/randomizer” , “feedback” , “5th add”, “pitch shift” and the classic “power crash”.
In the forum www.circuitbenders.co.uk I found another scheme based on the casper mod but with some adds.