in today’s episode of “el stupido stupids around”, our hero wants to look up something on a MBP 15 2015 (retina). problem is, there’s already a 2010 (fatso) occupying space on the desk. is hero gonna move fatso aside to achieve said goal? 'course not, close fatso and place the retina on top. haha look at my lazy ass being expeditious!
power on the retina and… black screen. no idea what’s going on as there are no status lights - thanks apple… is the battery empty, dead, wtf, no way, how can this be? bring over Magsafe 2 charger, plug in, try now… same thing. what the fuck, it’s dead? maybe open it and disconnect the battery and try with magsafe only…
in a rare flash of mindfulness hero unstacks the laptops and… there we are, screen lights up, plymouth’s decrypt screen is visible and all is good!
what happened is macbooks detect the screen is closed by way of magnets. so, a reed relay closes, SMC says “ok we closed, turn off screen”. since there was another macbook beneath it, its magnet array got detected and retina’s screen was turned off.
I was all ready for a tale of woe, with too much presure or heat breaking the screen of the lower one. Thanks for the laugh, and congratulations for working it out before breaking out the screwdriver.
I recently noticed the same phenomenon with Thinkpad T14 laptops. Took me a while to realize it was the magnets.