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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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2011 27" iMac screen is black, backlight is on.

Hello all! I’ve come across MANY posts of the same issue. Mine really isn’t much different. A little background.

I got this 2nd hand from a co-worker who’s son went off to college long ago. It was his sons, and he had it sitting in a spare room. He said if I could fix it, I could have it. He was going to toss it because the screen wouldn’t work. I have an electrical/PLC programming background, so I said “Sure”.

Well when I got it, the screen was working for me. So I went ahead and formatted/restored it to default. During that process the screen did go black, but came back after about an hour. I finished the restore. There were a couple more instances where it would go black, but then come back on, and now it has finally went off for good (I think).

Now, I went through the deep dive suggestions that another poster had put up:

I am at step 7, “Replace Display Port Cable.”

I just wanted to ask if there were any recommended checks, or just order a cable and test (they are cheap enough). Something to add, when I remove the Display Cable and try booting, the fan (GPU I think) goes to full 100% speed. When I reattach the cable, it goes back to controlled speed. Also, I witnessed the screen go black once, and it had a half screen of vertical colored lines, and then all went black.

Thanks again for any help! I purchase quite a few parts from here and follow a lot of the guides when repairing my family’s Apple products.

(Below is the Deep Dive list I came across)

Deep Dive

1. Verify boot chime present and fans running when computer powered ON. (Reset SMC and clear PRAM if necessary for proper boot up.)

Yes Power on self test OK.

Go to step 2.

No Go to Won’t Start Up symptom flow.

2. Verify if image is visible on built-in LCD panel, with adjustable backlight level.

Yes Video present. Verify system functionality and return to user or go to appropriate troubleshooting flow.

No Go to step 3.

3. Connect supported external display. Verify if image appears on external display when system is booted.

Yes External display detected by system. Video circuitry on logic board functional.

Go to step 4.

No Go to No Video symptom flow.

4. Verify if LCD backlight is ON by looking for faint glow from display when viewed in darkened room with brightness set at maximum.

Yes LED backlight is functioning.

Go to step 7.

No Go to step 5.

5. Shine bright (low heat) flashlight onto front of LCD. With computer powered ON verify if a faint image is visible.

Yes LCD panel functional but backlight is missing or dim. Remove LCD panel and inspect and reseat the

following cable connections:

-Backlight power cable

between backlight board and LCD panel.

-Vertical sync cable between backlight board and LCD panel.

-DC power cable to backlight board and power supply.

Replace any damaged cable.

Reinstall LCD panel and go to step 6.

No No image or backlight.

Go to step 7.

6. Power ON system. Verify if image is now visible on LCD panel with correct backlight level.

Yes Issue resolved.

No Replace LED backlight board.

Retest. If issue persists, go to step 7.

7. Inspect and reseat internal DisplayPort cable (between logic board and LCD panel).

Power ON system. Verify if image is visible on built-in LCD display.

Yes Issue resolved.

No Replace internal DisplayPort cable.

If issue persists, replace LCD panel. Run Apple Service Display Utility to verify the resolution of intermittent display flickering symptoms. If the Apple Service Display Utility fails, contact Technical Service Provider Support

Anything after that, you'd have to measure some voltages on your logicboard.

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Well did you go through that check list, especially the one on hooking up an external display?

This model has a repair program for the GPU (which, of course has now expired). If you determine the GPU has failed, I have had good luck (75%) doing a hot air work station reflow of the GPU.

https://9to5mac.com/2013/08/16/apple-ope...

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Yes, the external display does work when hooked up. I was at the point of trying a display cable. But just asked if there were any further tests before ordering a cable, then an LCD.

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Well, my serial # did not fall within the range of faulty GPU's, but that doesn't mean it's not the issue. I tried a replacement cable, with the same results. I've purchased a used LCD panel matching the exact LG model and rev. I will see if that takes care of it.

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I've had some success with disassembling the LCD panel, getting out the board that is connected with 2 flat cables. I wanted to replace it, but when I saw I had the wrong replacement, I put the original board back, closed it all up, put back all of the black tape and hooked it back up. Result : the lcd panel works again, as if by magic. I suspect it's the connection of those flat cables that are the problem after 7 years of heat cycling. It's still working, and only switched off because the automatic brightness control put it on full brightness, and the temperature went up too much. I could feel the heat coming off of the left/bottom side of the lcd panel, and of the backlight board on the left edge. It's fine now, I turned off the automatic brightness.

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Yes removing the cable from the LCD will cause the fans to rev up to max. This is because the cable also support the temp sensor. Without that sensor it jacks up the RPM to the max.


It definitely sounds like the LCD itself is starting to go bad. I’ve seen a bunch of LCDs that have the backlight fail and less that only has a working backlight. It is very possible though.

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Is there anything at the board level on the LCD itself that I can check? Like the TCon board or anything else?

Before I see what prices are on LCD's. Thanks!

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Joe will be eternally grateful.
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