Chosen Solution
Hello All, Bit of a strange one here, at least I think so. I have just purchased an iMac 27” 2013 model, it was sold to me as not booting.Fault finding process, Environmental, Hardware, Software or customer education, environmental and customer education ruled out. On to software; - used a known good version of 10.13.6 on a bootable Usb drive to boot the iMac - failed, normally this would prove software is not at fault, but there could be firmware issue if the iMac had a higher OS installed.- Command R / internet recovery will not load On to hardware;- Hard drive ruled out due to software fault finding- Ram ruled out, known good RAM installed still no change to fault- NVRAM reset performed, no change to fault Normally this would leave the logic board that would need to be replaced in order to get the iMac working, but here is the thing, the iMac loads into Ubuntu desktop from a bootable USB drive and using benchmarking tools I can confirm a working CPU and GPU. What would cause a Mac not to work with macOS but to work just fine with other operating systems? Thank you for your time.
You are likely hitting two different issues! Ubuntu messes with the Master boot blocks and boot loader of the drive so you can’t boot up under macOS. So you will need to nuke the drive with Mac Disk Utility and properly install a fresh macOS. But how?? You’ll need to boot up under an external bootable drive. I would start off with macOS 10.12.5 Sierra and the highest your system can officially run is macOS 10.15.x Catalina. Using another Mac download from here the macOS you’ll need How to get old versions of macOS and for example follow this guide How to create a bootable macOS Sierra installer drive make sure the USB drive has been formatted with Disk Utility with a GUID partition map and a Journaled file system. That should do it. If not leverage the Startup Manager using Option (⌥) Reference: Mac startup key combinations
