Sleep Mode
When the lid is closed the device goes to sleep mode normally. If this is not working properly, check the magnets on the LCD mod, bezel, or back cover.
These magnets come within close proximity to a sensor on either the motherboard or the daughterboard. If the magnets are not in the correct orientation or polarization it will fail to trigger the sensor and the device will not go to sleep. Usually flipping the magnets can resolve this issue.
For example, the Acer R721T has thin magnet on the right side of the LCD module. This magnet triggers sleep mode when the lid is closed and comes in near contact with the daughterboard.
If flipping the magnets does not work, the issue might be with the motherboard or daughterboard.