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Repair guides and support for 21.5" Intel iMacs by Apple.

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Black screen after resetting PRAM

Hello

I have iMac 21" 2011, it is working fine till yesterday. I was trying to boot it from USB but failed. After that I went to try a lot of options and read a lot of articles. One of them suggested resetting PRAM. I did reset PRAM and that was the end of my iMac. After resetting PRAM I only get black screen. I hear the startup chime and the keyboard is functioning and I hear sound when I click on it.

What to do now, I never though that resetting PRAM can destroy then device

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Is very odd the PRAM reset killed your machine. What was the exact procedure you have done? In which way the boot from usb failed?

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Please give us the model number and EMC number located on the botton side of the iMac stand.

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Please give us the model number and EMC number located on the botton side of the iMac stand. Hook it up to an external monitor and see if the GPU is generating a video signal. Why were you trying to boot from an external USB, what was going wrong?

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Hi everyone

EMC 2428

Model 21" mid 2011

I went for a workshop. The guy said it is GPU issue and he fix it using heat treatment .

Now the system is loading but after the loading page it goes to black screen

I just got fed up and for proving it, I asked him to do PRAM setting and after that the issue returned

My conclusion is that I need to buy new one instead of fixing it

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Mine is a 21.5" mid 2011 iMac A1311 EMC 2428 as well with the AMD 6750M 512MB GPU.

During bootup, mine was showing "stripe" lines with led me to believe that the GPU was going bad. I reflowed it in the oven for 9 minutes at 200C (~400F) as recommended by a youtuber.

After putting it back together and rebooting, the lines disappeared but the screen would go black again when trying to load the MacOS system. As a last measure, I reset the PRAM and that "killed" the GPU again.

So I'm guessing I need to find a new GPU.

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