Chosen Solution
Model - iMac 21.5 4k 2017 3.0Ghz i5 So I replaced the CPU with Intel i7-7700, I’m sure I followed the instructions carefully. After putting everything back the machine won’t power on, only 1 LED on the logic board came up. Tried a new power supply on, still doesn’t work. Tried changing the CPU back to the original one, still didn’t work I took it to diagnose at an Apple Authorized Service Provider and they told me that the power supply was non functional, used KGB PSU to test, and logic board did not respond. Any solution for this? Would appreciate any kind of help. At this point I don’t mind using the old CPU, just want the machine to work again.
It sounds like you damaged the logic board or the CPU housing. You should try to purchase a logic board with an i7 cpu and not upgrade.
Inspect the socket pins I’m suspecting you damaged a few (shorting)
The exact same thing happened to me last night. Only to find out after hours of rechecking everything that I forgot to plug in the tiny cable on the left side of the power board. It’s for the power switch. No wonder nothing happens when I press the button.
When you replace the CPU or GPU or PCH, you need to rebuild the firmware and the PCH timing need to reset. Once you tried to boot up, the machine goes haywire because it doesn’t recognise the CPU. It got nothing to do with power supply or logic board. There are very few people can build the firmware and according to Dan, Louis Rossmann may be able to rebuild it. I am not a celebrity so I only do the work for people who know me and trust me for what I do. If you are in California SF Bay Area, I can do it next day service but if you are from other part, you need to figure out a way to get it here.
