This guide is for hinge type K26. This hinge type is found on the following models:
Some colors in the pictures may differ for your model. That is fine, what matters most is the shape of the hinge piece.
The plastic hinge mechanism must be oriented as shown for it to fit onto the metal keyboard hooks. Notice the two indents on the edge of the white piece should be at the bottom.
Hook the top edge of the inner black hinge over the top two metal hooks on the base of the keyboard.
Snap the bottom of the hinge into place, one side at a time. In this example, the bottom left side is being secured first. The bottom left and right sides of the plastic hinge should be clipped under the metal notch protruding from the base of the keyboard on each side. You can now check that the hinge works by flexing it up and down; it should pivot easily at its axis.
If your keyboard is missing the rubber spring piece, place it in the center of the hinge. It will be held in place by the surrounding key and hinge.
Align the key on top of its place on the keyboard, and press down evenly. All four corners of the key should click into place.