Posted: Mar 17, 2019 3:23 pm
by The_Metatron
My mid-2010 27” iMac started blacking out recently. Random crashes to black screen, sometimes during boot, sometimes it let me get as far as logged in. I could hear the hard drive working in the background, but the screen would go black. The only recovery was a hard restart.

It seemed to me that the screen went blank whenever some new process started and made a demand on memory resources. I noticed that behavior when I could get as far as logged in to my desktop. Clicking on any icon to start a process caused an immediate screen blackout. This indicated misbehaving RAM to me.

The remedy was to reseat the four RAM chips. I suspect one of the many hundreds of contacts across those four chips went high resistance. Physically reseating them solved the screen blanking problem.