iMac 2011 21.5 inch only 1st led ON

Question

iMac Intel 21.5" EMC 2428 Mid 2011

Model A1311 / Mid 2011 / 2.5 & 2.7 GHz Core i5 or 2.8 GHz Core i7 Processor

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Shovelcheco @shovelcheco

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crwdns2931729:0crwdne2931729:0: yesterdayMaw 7, 2025

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iMac 2011 21.5 inch only 1st led ON

Hi!

I have one (well... now almost 2) iMac's 2011 21,5". I bought the first one with windows running on it due to a faulty GPU. So i decided to make it run like a charm and also make some upgrades.

I've bought a WX4150 4GB and 32gb of compatible ram 1333 mhz, but in the first build i kindda broke a capacitor on my new GPU, got electrocuted and made the PSU smoke a little.

So i ordered: a new MOBO, GPU and PSU. Put everything together carefully, but only DX LED 1 lights up. I have another identical iMac that i bought trying to use the better looking case, so i have 3 mobos, 2 PSUs, and basically spare parts for everything else.

I've tried:

Booting with and without mobo battery
Using both CPUs (were working on windows)
Replacing power cables (outlet-psu and psu-mobo)
Booting with and without RAMs (with originals and the ones i boght)
2 power buttons (were working on windows) and jumping power pins
With and without SSS/HD

I know ill have to flash my GPU, but i dont know if my DX LEDs should only light 1st one before this flash happens. Can someone help me please?

Tomorrow ill get a macbook borrowed in case any solution needs some bootable made from a mac (whis is my plan for the headless flashing aswell)

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score 0 · Answer 1 · 2025-07-08T05:16:28-07:00

Yes you need the proper version of macOS to run this system if you want to run Mac Apps. The highest version I would install to start with would be Sierra (10.12.x) as you will need to fully wipe the drive to rebuild the GUID/Journaled file system (HFS+) in the process the recovery partition will be created. Then later you can upgrade to High Sierra (10.13.x)which will convert the systems firmware to support the newer file system APFS. then using a shim service like What is OpenCore Legacy Patcher? Guide #01 you can run still newer macOS's!

So using the working Mac create a bootable OS installer with Sierra onto a USB thumb drive so you have a working macOS to even try booting the system.

One of the risks in this series is trying to find replacement MXM GPU boards as they are getting quite hard to find that are still working as both AMD & Apple tried to hide a chip failure then to compound things people out stretched what this GPU could support for Apps without melting down! So you have less than a 50/50 chance getting a working board. The next hurdle is finding an alternative board that Apple supports with there OS drivers that limits you or you get a better board that only runs in compatibility mode not gaining the full ability of the better board.

And yes, you may need to fix the boards firmware so the system accepts it.

So with the proper RAM and a working drive (either a HDD or SSD in the primary drive bay) as well as the needed and working PRAM battery and the display fully connected and the created USB thumb drive connected. You should be able to boot the system getting into the onboard diagnostics using the startup D key. Given the fact the GPU is Blown you will need to run the system in Safe Mode to bypass the loading of the GPU driver.

Mac startup key combinations

The system board also offers a set of diagnostic LEDs. But you need to have the display connected via a set of extension cables or carefully holding the display away so you can spy them. Be very careful! As the cables are not vers long and when display drops the force tends to damage either the logic board connector's or the cables them selves.

iMac Intel 21.5" EMC 2428 Mid 2011

iMac 2011 21.5 inch only 1st led ON

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