Pull straight up on the top main board and the two boards will disconnect. The connection between them is circled in light-blue. Notice the joystick controller is on the top main board.

The bottom board is still secured with one screw.

Remove one PH0 screw.

Remove the plus (+) button.

Remove the X, A, B, & Y buttons.

The bottom board can be removed as well as the last rubberized bottom three buttons.

Notice that this top main board has the same processor as the main motherboard of the left controller. It is MM32L052NT which is a ARM Cortex(TM) M0.