As promised, this is an extra step for the sound and On/off ribbon. Be sure to get a very slim blade to take it off (not so sharp to avoid cutting the ribbon).
Of course, be sure to slide it in running along the metal (black). Otherwise, the blade will separate the buttons from the ribbon.
Lift it up gently to get the connector of the ribbon out. If you fold the ribbon in this operation, it will not work correctly. It is best to order one with the touch screen (2 US $ more or less).