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

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iMac EMC2428 black screen

Hi,

I have an iMac 2011, 21,5" EMC 2428.

Right after the boot chime, the backlight goes on for a short period and then stays off forever. It seems that the LED backlight isn't working anymore, because if you use a flashlight you can see everything on the internal screen.

There is an interesting situation where a backlight appears in a short time when it is woken up.

I have opened system to check the onboard diagnostic LED’s 1 ~ 4, all are turned on.

Has anyone encountered the same situation?

Thanks.

Richard

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You’ll need to replace the backlight LED driver board iMac Intel 21.5" EMC 2428 LED Driver Board following this IFIXIT guide: iMac Intel 21.5" EMC 2428 LED Driver Board Replacement

Update (01/08/2019)

What does the NVRAM require to hold its settings?

Block Image

I would start there.

Imagem de iMac Intel 21.5" EMC 2428 LED Driver Board

Produto

iMac Intel 21.5" EMC 2428 LED Driver Board

$29.99

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Thanks for your help.

After a few day for test.The backlight if finally turned on when i reset the NVRAM.But when i restart up imac,it still back screen. is software problem or hardware???

por

Thanks very much...

Because I don't know how to fix the black screen condition. Should I try things like resetting NVRAM, running AHT...

I’ve now replaced the PRAM battery, still no changes.

I found a strange situation where the backlight is turned up to maximum and the backlight automatically option is disabled. The screen backlight is coming back on.

What happen? LED driver board error? LED Panel ?

por

Did you replace the LED driver board? Check the cable to the display (may need to be replaced). The original diagnostics was correct the LED driver board is not working correctly.

por

I had replacement it and buy it from china TAOBAO.

Maybe it used. So i need to by another.

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I think you'll need to get a new one too.

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Hello,

It’s possible that it is a bad AMD graphics chip as well. If your iMac has the HD 6970 or HD 6950 this a really common failure, Unfortunately there were never updated cards for this machine to fix the GPU defect. If there is no image it’s likely the GPU.

You should check if you have an image on the screen, by using bright light held against the LCD panel. You should be able to see something on the screen if the panel is getting an image I would definitely look at replacing either the backlight driver board.

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@brycewalter - Did you read the OP's description? "if you use a flashlight you can see everything on the internal screen."

Often times I find the thermal pads cooked on the bad graphics boards. When I talk to my customers I often find they are heavy gamers. While I'm not saying this is the cause exclusively, it's a good sign post the system was being pushed beyond what it was designed to handle vs a defective GPU chip.

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I missed that, thank you.

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Hello,

same problem here.

The iMac works with external display and also do detect its internal display. Tried to change the backlight inverter board but same problem. Now even with the flashlight I can see nothing. Can be really the GPU?

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I'm a bit lost in your condition. How about creating your own question as this one is quite old.

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