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Model A1419 / EMC 2806 / Late 2014 or Mid 2015. 3.3 or 3.5 GHz Core i5 or 4.0 GHz Core i7 (ID iMac15,1); EMC 2834 late 2015 / 3.3 or 3.5 GHz Core i5 or 4.0 GHz Core i7 (iMac17,1) All with Retina 5K displays

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iMac not powering up. USB port powers led light.

Hi,

I have a 27” 5k iMac (late 2014, i7 4.0, 295x 4gb). Tonight, the unit froze so, I rebooted it. After I power cycled it, the power would click off after only a few seconds. I did this cycle a few times. Sometimes if I let is sit unplugged for a while, after reconnecting power, I could get it to progress to booting up into macOS. But is locks up shortly after that. When plugged in, the usb is outputting power ( I have led light that I use, powered from the iMac ). I am guessing it’s either a bad power supply or logic board.

Any advice?

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@gtesserac post a couple of good pictures of your logic board as well as your power supply. That way we can see what you see and maybe even find things for you to check Adding images to an existing question

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This symptom often leads to a logic board power issue. Likely a tantalum capacitor has failed within one of the power rails. Often times you can see visible damage in one of the caps which are in a row sizable blackish grey or yellow blocky rectangle SMD device with one side edge beveled or marked with a line to show its polarity.

Unless you have the tools and experience micro soldering its likely best to seek out someone with deeper iMac repair skills.

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