Dell 5100cn Color Laser Printer - Manual (Page 72)

7. Insert the controller card into the printer.
8. Tighten the three screws on the controller card from the back side of the printer. The two screws on the upper side
are different in shape from the one on the lower side. Be careful not to confuse them.
9. Reattach the paper tray cover to the back of the printer.