Chosen Solution
I swapped the screen (lower resolution, glossy) on my Mid 2012 Unibody MacBook Pro with a screen from the 2011 model, which is the high resolution, anti-glare one. Everything works fine except the laptop no longer sleeps when I close the lid. I put the old screen back on and the functionality is working again so I assume it is something to do with the new screen. I was led to believe this swap would work, are the magnets not in the same place?
Too much coffee or tea for your system! There is a Magnet in the lid that meets up with a Hall sensor within your system. You may need a new HD SATA cable assembly which holds the Hall sensor as well MacBook Pro 15" Unibody (Mid 2012) Hard Drive Cable Following this guide MacBook Pro 15" Unibody Mid 2012 Hard Drive/IR Sensor Cable Replacement But! Before we go down that path Let’s make sure the magnet is present and in the correct location! You need a steel paper clip and a small earth magnet use the paper clip to locate the magnet sliding it along the face the the display bezel space along the side. Once you find it carefully fold the display down so you can locate the mating surface (don’t fold it down to far!) I use a china marker then with the system running slide the magnet across the case slowly passing across the space did the display turn off? If not slide the magnet up and down for that location did you find the sensor? If not then we know the sensor has failed. If the location is different then we know someone replaced the LCD panel and the magnet was incorrectly placed or maybe they forgot the magnet!
