2011 iMac restarting during macOS setup
Recently got hold of a 27" 2011 iMac. I have installed a blank SSD and using a bootable USB stick I went through the process of wiping the SSD and installing macOS High Sierra. I've done this a few times before on other 2011 iMacs and it went fine on this model.
However, when booting into the actual SSD, the mac randomly restarts once you get to the High Sierra setup page. Sometimes it'll let you get a couple of steps through it (choosing language, getting past accessibility) but after a few mouse clicks it'll black screen and restart itself, with no error messages.
It is worth noting the guy I bought this off said he experienced the same issue with the installed High Sierra he had on the old HDD - it would get to login, or sometimes to desktop and then crash as above.
Things I have tried:
Resetting SMC and PRAM, no changes.
Using the bootable to install HS on a different drive (a second USB): this produced exactly the same results, the install went fine (albeit slower obviously) but then booting into the second USB to setup High Sierra crashed in the same manner above.
Skipping the High Sierra step and going straight for Monterey. I have done this before and everything went perfectly from my 12,2 USB, going through the multiple expected restarts and progress bars, until I actually got to the Monterey setup page, and only then the iMac exhibits the same behavior as above with High Sierra. I did leave the initial Monterey setup on screen for a while to see if it would crash without me doing anything, and it seemed to be ok. However once I attempted to get through some of the steps, it crashed as above.
My troubleshooting so far:
I suspected a RAM issue. The RAM in the machine is 2x4gb DDR3 1333mhz but not OG apple. I have tried a few other sticks and the same thing happens, but the only ones I have lying around (that I know work) are 1066mhz or 1600mhz speed and so I could just be recreating the same issue. I have also tried using each of the RAM sticks individually - this actually results in the iMac crash happening earlier, during the Apple logo loading bar, and generates a jagged weird screen artifact just before it restarts. Occasionally while trying the different RAM combinations, I would get the three beeps of failed memory integrity, but a restart would solve this often without actually changing the sticks from whatever combination I was trying that time.
I have, sadly, tried the RAM into another iMac, and that one does work :(
As for the usual culprits of power supply and GPU, I have seen failed GPUs before and the fact that this mac is able to display recovery and setup perfectly fine leads be to believe the GPU is ok. Similarly, the initial installs from the bootable USBs took a while, leading me to trust that the PSU is not being temperamental.
Given all the above, my question is: what could cause a crash restart, but ONLY in macOS setup (or login screen, if my seller is to be believed)? Why was the iMac perfectly fine to do the bootable USB install, both from HS and Monterey, but then dies during setup? Does setup begin to utilise RAM, provoking the crash?
Any help appreciated
Earlier Mac models
