iMac Random Shutdowns with Various other issues

A few weeks ago, I received an early-2009 24” iMac with the 2.93GHz Intel Core 2 Duo.

I don’t remember what OS was on it, but it was described to me as “overheating and shutting down randomly”. I found that it would boot to the home screen, then almost immediately shut off. One time, there was enough time to enable the “restart after power loss” option, and the iMac did not restart, meaning the PSU is fine.

By unplugging the 1TB HDD, the iMac stayed on the “?” blinking folder for over 30 minutes just fine. Once I got it home, I completely disassembled it and cleaned it, along with fresh thermal paste. I also replaced the PRAM battery with a new one as the old one was at 0.1v when I tested it with a multimeter.

At this point, I thought it was a courrupted hard drive issue, as attempting reinstall the OS from the recovery partition failed. Wiping the drive through Disk Utility did not work either. I ended up wiping the drive connected to my Windows PC, and the drive came up as healthy.

I successfully managed to install macOS Catalina, using DosDude1’s Catalina Patcher Tool, but upon completion of installation, it once again, shut down. At this point, I noted that the iMac was EXTREMELY hot, even though it was clean and all fans were spinning. I let it cool down and unplugged a temp sensor so the fans would run at full speed. Now, it refused to even boot properly, shutting down at the loading bar. After a bit more troubleshooting, the display’s colours became distorted and started flickering.

At this point, I’m thinking the motherboard has failed. I’ll replace the PRAM battery again, and try with a new SSD instead of the hard drive. Otherwise I might just part it out and make some profit that way.

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