I am searching for an answer to my question please. So far I have not been able to find any reference to the sensor board online or from Dell! The official Dell Service Manual does not even mention the device. My question: is the 10729-1 sensor board switch supposed to turn off an external monitor as well as the laptop screen or only the laptop screen? I have a dark screen all of the time but an external monitor displays video as advertised. When I place the lid magnet close to the sensor, MY external monitor momentarily goes dark but then comes right back on. I am trying to determine if my sensor board is bad or if my LCD is bad. Thank you.