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Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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No power to LCD, black screen failing GPU

Hi all you smart iMac enthusiasts I also have a 2011 27” (2429) iMac with no display fault (black screen).

After reading so many threads on iFixit and beyond I would like some help in getting up and running with the least amount of cash investment.

I bought this iMac second hand for $100 AUD knowing full well that it was faulty but i couldn't help myself as it came with 16gb ram and the i7 variant but no hard drive.

The symptom described to me were of graphical artifacts on the screen and that years ago apple had replaced the GPU, my guess is that this second 6970m 1024mb was also now failed.

So upon taking the glass off I noticed only 4 screws holding on the lcd which had been stripped a bit (uhh ohh i thought) but upon removing the 4 cables i was presently surprised to see that they looked in good condition, the vsync cable did seem to slide in and out easy.

I put in a 2.5” hdd that has high Sierra.

Booting with the screen connected i get boot chime, no display, no sign of image on screen under torch light, 1,2 and 3 diagnostic LED are solid green.

My next step was to go out and buy a mini display to HDMI, i come back and boot it up connected to my TV and get to the blurred out log-in screen. After powering off and disconnecting the LCD i rebooted and get the visible log-in screen and start using Safari to download a fan controller.

Graphical glitches start with pixelated cubes until soon after the mac locks up.

So I know that i need to replace the GPU (i will try baking it first) but what is everyone's take on the LCD?

I’m wondering if it will will work once I replace the GPU?

I’m hoping its not this issue as solved by Yako ( link deleted so the iFixit robot diesn’t delete my post) Google yako ifixit post, its in regards to a blown ferrite chip which is responsible for the 12v on LCD Display port.

If it was the backlight strip faulty should i see a faint image under torch light?

Any suggestions and comments welcome.

Thanks,

Croupier

Update (02/05/2021)

Ok so thermal paste came but no thermal pads yet. I couldn't help myself so i stripped the iMac down and reapplied to cpu first, might as well yeah.

Removed the gpu and gave it a good scrub and ethanol bath and decided to bake it now in preparation for the thermal pads hopefully arriving on Monday.

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I was listening to music and having a few g&t's during the teardown enjoining tinkering preheated the oven to 200c and popped the card in, I hey googled a 10 min timer not realising it didn't go through and got onto cleaning out the fans.

Finished the fans and went to get another drink, opps, completely forgot about the gpu while in fan clean mode ? oh well 25 minutes, well done instead of medium rare. I'm curious to see if I completely stuffed the card so decided that ill put it all together without paste or pads for a quick 1 minute test.

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Mmmm toasty

I hook it up to the tv via mini port/hdmi without screen and boom, perfect working order, no glitches log in everything is hunky dory.

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Shut down and install lcd screen, same same, no sign of life no image under torch.

Ok well at least the gpu is good move on to stage 2, cables? Backlight board? What else.

Out if curiosity i tried hooking up my 2010 lcd, the one compatible cable from backlight board, as i expected no sign of light.

Whats do you think i should try next?

Cables look good some im leaning towards backlight board.

Is there anyway to test it with a multimeter before buying a replacement?

Cheers all.

Note: I posted this as an answer because my comments are apparently too long to post.

EDIT: Hey im thinking that my working 2010 backlight board work in the 2011?

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Will it?

EDIT 2: Yes indeed it will. Even though the boards look different component/screw and rubber mounting-wise the are interchangeable between 2010 and 11.

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I put my 2010 backlight board in the 2011 but still a dead screen while my 2010 now enjoys a upgrade 2011 backlight board and is alive and well.

So we are narrowed down to 2011 LCD cables/backlight strip or 2011 MOBO issue?

Any suggestions iFixit peeps.

Cheers, pretty sloshed now but had fun, time to crash.

Croupier

Update (02/05/2021)

Connecter looks good, what do you think?

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I'm no expert on iMac repair like Dan is, but the one experience I have from Mac screen issues was because the contact pins for the motherboard ribbon socket had shorted and actually had burned away. I'd make sure to very closely inspect the motherboard socket to make sure that isn't part of the problem.

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@reedcrosby - Yes a cable incorrectly inserted can damage things! I also find people pull a bt too much on the cables when taking the display off which can pull the logic board connectors damaging them.

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@croupier - You only need the TIM on the GPU chip, the person who serviced it before over did it! The Thermal pads are only needed on the VRAM chips.

The connecter looks OK, but let's take a look at the cable end. Keep in mind the LVDS cable only deals with the LCD, the other cables are used (LED backlight driver & vertical sync cables).

I would place a flashlight against the screen to see if you can see the faint image of your desktop and icons. Do you?

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@danj

Couldn't see anything with a flashlight but i will try again

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No way!!! I’m so happy. I have a working 2011 27” i7 imac with 16gb ram for $76 USD plus paste and pads.

It must have been the LVDS flex cable. By fully removing it from the lcd panel for the photos and then putting it it back I reinstalled the panel and was going to do the flash light test on the desktop when to my delight a white screen ?

I have had that panel in and out so many times but had never full removed the flex cable, maybe it was loose at the connection to the lcd but it looked sweet and taped down ECT. If this problem persists I'll buy a new cable, until then im happy mac'n.

Thanks for everyone's input and i hope this might help others in the future.

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Focus on the GPU board, your screen is likely OK. But you hit a wrinkle! It does sound like the systems firmware was not updated to the newer version which supports APFS boot volumes. Your SSD with High Sierra was upgraded to APFS during the install process (the firmware would have been as well) on the system which you had it installed. As the current firmware on this system can only hand HFS+ bot volumes.

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Waiting on thermal paste and pads, will then try the bake and report back.

Hey Dan, do you know if i can plug and play with my 2010 imac gpu without removing it from the heatsink? The only difference I can see is the screws mounting to the board are front accessed.

Cheers.

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If the replacement comes with the heatsink mounted you could swap out the full assembly. Rarely do you find them with the heatsinks.

If you are trying to take the GPU board out to given it a broil (pun), you'll need to first remove the full assembly then you take the board off the heat sink and fully clean it of anything that would melt.

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LCD side

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MLB side

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I appreciate the help, thanks everyone, keep the suggestions coming.

EDIT: looks like maybe some pulling on the back of the MLB side connector?

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It would be nice if they sold an adaptor to go from 2010 to 2011 connected type, wishful thinking.

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EDIT: logic board socket

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Jesse será eternamente grato(a).
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