I usually post finished circuit-bent creations, but here's a work in progress and some documentation. The Yamaha PSS-270 is a FM keyboard with a multitude of cool presets and an analog chorus. Here's the first round of discoveries: an octave drop, randomize function, chorus depth, chorus morph feedback, overdrive, and a sustain twister. The connections are marked with colored circles, with an explanation of the connection provided for each color.
I found a chorus speed modification and added it to the diagram above. A randomize function was also added, as well as information on limiting resistors. Limiting resistors are placed in the circuit between the potentiometer and the contact points to protect the circuit. They are also used to tune control ranges.
New controls fitted to the hand-painted faceplate
BaumDerProllige says similiar chorus modifications also work with the Yamaha PSS-570.