Mid-2011 iMac 27" - diagnosing black screen problem

[Locke357]

The computer boots, I hear the startup tone, but the display stays black. On occasion the display turns on for a brief amount of time, I was able to run First Aid in disk utility (nothing), and even erased the HDD and reinstalled MacOS. But before long the display went black again and hasn't turned on since. The caps lock light can turn on and off on the keyboard, but not the num lock.

I've had this computer for 10 years now and the only issue I've ever dealt with was replacing the HDD with a replacement when it died.

I know this model has a GPU with known issues (AMD Radeon HD 6970M 2gb GDDR5), and I'm still peeved I missed the recall. From the searching I've done it seems like it may indeed be the issue, I just want to be sure so I don't blow $130 on getting a replacement GPU.

Specs:

iMac 27-Inch "Core i7" 3.4 (Mid-2011)
MD063LL/A - iMac12,2 - A1312

3.4 GHz i7-2600 Quad Core
12 GB 1333 MHz DDR3 SDRAM
1 TB HDD
AMD Radeon HD 6970M 2gb GDDR5

I am the proud owner of this computer, I've nicknamed it "The Beast," and while I've since moved on to game on a PC I built, I use this computer for streaming and light gaming for my kids. I'm not ready to say goodbye yet so please help me diagnose the problem. Thanks!



If it is indeed the GPU, wdyt about these to replace it with?

K2100M
https://www.ebay.ca/itm/175395520130

K1100M
https://www.ebay.ca/itm/154448606238

 

[Nguyen Duc Hieu]

If it is indeed the GPU, wdyt about these to replace it with?

K2100M
https://www.ebay.ca/itm/175395520130

K1100M
https://www.ebay.ca/itm/154448606238

1. It is indeed the GPU, or the LCD backligkt power board.
2. I wouldn't want any of those. Search for K3100m or K4100m, a little increase in price but better performance and more "Mac native" feelings. Choose those that have been flashed with Mac compatible vBIOS.

 

[Locke357]

1. It is indeed the GPU, or the LCD backligkt power board.
2. I wouldn't want any of those. Search for K3100m or K4100m, a little increase in price but better performance and more "Mac native" feelings. Choose those that have been flashed with Mac compatible vBIOS.

Something more like this? https://www.ebay.ca/itm/385075606827

How would I troubleshoot if it was the LCD backlight instead? Thanks

 

[Nguyen Duc Hieu]

Something more like this? https://www.ebay.ca/itm/385075606827

How would I troubleshoot if it was the LCD backlight instead? Thanks

Yeah, that kind of thing.

I've read somewhere that you can use a powerful light source pointing toward the LCD panel, if only the backlight is bad, you will be able to see a part of the login screen.

I simply assemble the LCD panel to another working iMac, to check the quality as well.

 

[farscaper]

Yeah, that kind of thing.

I've read somewhere that you can use a powerful light source pointing toward the LCD panel, if only the backlight is bad, you will be able to see a part of the login screen.

I simply assemble the LCD panel to another working iMac, to check the quality as well.

Hello did you ever figure out why the LCD is randomly turning off?

Here is my experience with that

Post in thread '2011 iMac Graphics Card Upgrade' https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/post-32065871

 

[GidroGen]

Hello everyone!

I'm facing a serious issue with my iMac 27" from 2011 and can't seem to find a solution. Here are the main problems:

- All fans are running at maximum speed.

- The CPU is throttled to 1.7 GHz.

- The GPU is running at only 20% of its capacity.

- After waking up from sleep mode, everything works normally for about 10 seconds, but then the problems come back.

Here’s what I’ve already done:

- Replaced the CPU (with an i7 2600).

- Replaced the logic board.

- Installed new RAM.

- Replaced the SSD (from a Samsung 840 EVO 500GB to a Samsung 870 EVO 1TB).

- Installed a special temperature sensor for the SSD.

- Reinstalled macOS High Sierra.

- Reset NVRAM/PRAM and SMC multiple times.

I’m using *Macs Fan Control* and *Intel Power Gadget* for monitoring, but nothing changes: the CPU stays at 1.7 GHz even under load, and the GPU runs at minimal capacity.

Has anyone encountered a similar issue or has suggestions on what else I can try? I would really appreciate any advice or help! Thank you!