Adjacent to the disk drive cable, unplug a 2nd flat cable from the main board, as seen here.

Also unplug the 3 miniature connectors shown in the photo.

Also on this end of the board, unplug the two miniature connectors going to the keyboard, shown circled in this photo.

On the opposite end of the main board, unplug a 3rd flat cable, seen here.

Also unplug the adjacent power supply connector.

Here, the two connectors are unplugged.

Forward from the power supply is the small, after-touch board.  Unplug its connector.

In this photo, you can see one corner of the main board, on the left.  Note where a mounting screw has been removed.

Here you see the board with the mounting screw still in.

It's one of 3 screws you must remove from the front edge of the Printed Circuit Board (PCB).

Also, unplug the miniature connector next to this screw.