Hi
I have not-so-random shutdowns problem with my 2014 Retina 27" iMac. When i try to install a fresh install of Catalina from USB onto the internal Apple SSD, first stage of the install works fine then at the installation after the first reboot when the ETA bar is shown it will reach the end but i get kernel panic when it's done and it reboots by itself. Then i am stuck in this loop forever, ETA-->reboots-->ETA-->reboots......
Trying to install Windows 10 is pretty much the same, first sage of the install works fine then after it reboots and installs hardware stuff it reboots and then installation gets corrupted.
I searched for problems on these iMacs on the internet and random shutdowns problems seem frequent with these models. Most of the time the solution is to replace the power supply. There are 2 manufacturers for the PSU: Delta and LiteOn. If one is better than the other is not clear, the problem seems to happen with both anyway. So i purchached a LiteOn one from ebay thinking that i might have a Delta brand inside but it was a LiteOn inside my iMac. Anyway the new power supply did not change anything, still getting these annoying shutdowns. Either the new psu has the same defect or the problem is not the psu. Also, most of the posts i saw had to unplug the iMac from AC to do a SMC reset to be able to start the mac again, not me. The iMac just reboots out of nowhere and almost never gets to the desktop.
List of things i tried:
- Resetting the PRAM a million times.
- Resetting the SMC less than a million times but not far from it.
- Running the diagnostics: it found nothing wrong (can it find anything at all anyway...)
- Running EtreCheck. I see people using that often to troubleshoot. Did not find anything anyway.
- Re-installing OS from Internet Recovery. It installs but still gets stuck in a shutdown reboot loop with ETA progress bar...
- Removing the Apple SSD in case it is causing the issue. Did not help...
- Booting already installed OS (Big Sur beta, Catalina) from USB hard drive: gets to the desktop, no graphical glitches or anything weird, freezes after 1 min max and reboots.
- Booting in Safe Mode works and seems to last for a long time without locking up.
Now after replacing the psu and seeing that the iMac was still shutting down i thought that it must be a GPU failure or a bad capacitor feeding the gpu like the 2011 15" MacBook Pros. A lot of 2009-2011 iMacs have faulty gpus that freeze when initialized during boot sequence but these iMacs can still get to the desktop when booting in safe mode albeit really slow.
So one last thing i tried yesterday:
I booted in Safe Mode and quickly changed the resolution to 2560x1440 (low resolution not scaled) instead of the native 5120x2880 and rebooted normally. The iMac has been running fine for more than 2 hours yesterday and still works fine this morning without any shutdown issues. I ran Cinebench, Geekbench, Unigine Heaven (in 1080p) and it is stable. I pushed the iMac a little more by setting the resolution to 3200x1800 and ran Unigine Heaven windowed in 720p while watching temps and other sensors in iStats and it froze 1 min or so after starting the benchmark. So my best guess is that it really is a Power Supply problem and i just bought a used one that has the exact same problem.
Here are the stats just when it froze in case you can find something strange. PSU is rated for 300W, 174W should not be a problem...
I have not-so-random shutdowns problem with my 2014 Retina 27" iMac. When i try to install a fresh install of Catalina from USB onto the internal Apple SSD, first stage of the install works fine then at the installation after the first reboot when the ETA bar is shown it will reach the end but i get kernel panic when it's done and it reboots by itself. Then i am stuck in this loop forever, ETA-->reboots-->ETA-->reboots......
Trying to install Windows 10 is pretty much the same, first sage of the install works fine then after it reboots and installs hardware stuff it reboots and then installation gets corrupted.
I searched for problems on these iMacs on the internet and random shutdowns problems seem frequent with these models. Most of the time the solution is to replace the power supply. There are 2 manufacturers for the PSU: Delta and LiteOn. If one is better than the other is not clear, the problem seems to happen with both anyway. So i purchached a LiteOn one from ebay thinking that i might have a Delta brand inside but it was a LiteOn inside my iMac. Anyway the new power supply did not change anything, still getting these annoying shutdowns. Either the new psu has the same defect or the problem is not the psu. Also, most of the posts i saw had to unplug the iMac from AC to do a SMC reset to be able to start the mac again, not me. The iMac just reboots out of nowhere and almost never gets to the desktop.
List of things i tried:
- Resetting the PRAM a million times.
- Resetting the SMC less than a million times but not far from it.
- Running the diagnostics: it found nothing wrong (can it find anything at all anyway...)
- Running EtreCheck. I see people using that often to troubleshoot. Did not find anything anyway.
- Re-installing OS from Internet Recovery. It installs but still gets stuck in a shutdown reboot loop with ETA progress bar...
- Removing the Apple SSD in case it is causing the issue. Did not help...
- Booting already installed OS (Big Sur beta, Catalina) from USB hard drive: gets to the desktop, no graphical glitches or anything weird, freezes after 1 min max and reboots.
- Booting in Safe Mode works and seems to last for a long time without locking up.
Now after replacing the psu and seeing that the iMac was still shutting down i thought that it must be a GPU failure or a bad capacitor feeding the gpu like the 2011 15" MacBook Pros. A lot of 2009-2011 iMacs have faulty gpus that freeze when initialized during boot sequence but these iMacs can still get to the desktop when booting in safe mode albeit really slow.
So one last thing i tried yesterday:
I booted in Safe Mode and quickly changed the resolution to 2560x1440 (low resolution not scaled) instead of the native 5120x2880 and rebooted normally. The iMac has been running fine for more than 2 hours yesterday and still works fine this morning without any shutdown issues. I ran Cinebench, Geekbench, Unigine Heaven (in 1080p) and it is stable. I pushed the iMac a little more by setting the resolution to 3200x1800 and ran Unigine Heaven windowed in 720p while watching temps and other sensors in iStats and it froze 1 min or so after starting the benchmark. So my best guess is that it really is a Power Supply problem and i just bought a used one that has the exact same problem.
Here are the stats just when it froze in case you can find something strange. PSU is rated for 300W, 174W should not be a problem...
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