2011 iMac shuts down after booting to desktop
Recently, iFixit had diagnosed an issue with the 2011 iMac as being the dreaded GPU fault. Instead of replacing or reballing the card, I bought another used unit and switched drives, and I was back to work. I have since replaced the iMac with a Mac Pro, sold the replacement iMac and wanted to try and repair my original iMac.
I did the disassembly and followed a guide to “bake” the video card. It seemed to work as the Mac now booted up to a stable desktop. To test the repair, I left it on for 3-4 days and it would always come out of sleep. I noticed that there was a software update, so I did the update (High Sierra 10.13.6). Since this update, the machine will boot up to the desktop, work fine for a few minutes, then get a sleep window (randomly) and turn off. Before the “bake”, the iMac would get about 50% through the startup, present a solid gray screen and re-boot automatically in a continuous loop.
Is this just a different symptom of the GPU video card or is this another isolated issue as the machine now completes the boot cycle? Any suggestions on more in depth diagnosis?