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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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No video on internal and external display

Can anyone help me in solving this issue?

The iMac is starting up:

I can hear the chime

The display stays blank (it is completely off), the external display connected through thunderbolt port and hdmi cable says no signal.

I opened it:

The 1st and the 2nd led are on when the internal display is connected

The 1st, the 2nd and the 3rd led are on when the internal display is disconnected

Internal battery is 2.85V

The OS seems to start when internal display is not connected as the wireless keyboard power on and seems to be connected

The fans run full speed

An assistance manual suggests to replace the display port flat cable, or the GPU or the logic board.

Before wasting money, I would appreciate some suggestions from you.

Thanks you in advance.

Update (09/13/)

I took some pictures. They are not very clear (tomorrow I will try with a microscope) but it seems to me there is some problem on the male connector at logic board side.

What do you think about?

calbe pictures

Thanks in advance

Raffaele

Update (09/15/2015)

I finally was able to take some pictures at the microscope, I added them to the shared collection linked in the previous message.

The cable ending at board side showed a little bending which I was able to fix, the last two pictures refer to the fixed connector.

After connecting again everything it worked for a while: all 4 LEDs were on and the display showed the gray apple and the progress bar. But after a few seconds the display and the 4th led turned off again. No signal, everytime, to the external display. Should I perhaps apply any special procedure to activate the external display?

I also noticed that after a few minutes of trials, booting and shutdowning, also the 3rd led goes off. Now, whatever the display is connected or not, only 1st and 2nd led are on.

I really don't know what else doing. Please, help me.

Thank you in advance

Raffaele

Update (09/16/2015)

The 4 last digits of the Serial No. are: DHJF

Model is EMC 2428.

When I got the video signal (it was for short) the external display was connected (thunderbolt port to HDMI adaptor) but no signal was detected by external display. Moreover, with 3rd LED off or on the external display never gets a video signal.

Update (10/18/2015)

After trying a hot air reflow on my GPU, this is the updated status of my iMac:

After start up and chime sound, third led seems to be on stable over time

I can connect via ssh to the Mac, logging as root.

The content of the hard disk seems to be integer.

But the led panel is completely off.

Now that I can log into my iMac, is there anyone who can suggest me what to look for to understand why the led panel is off?

Thank you

Update (10/18/2015)

Hello everybody, I updated my post as now the iMac seems to be working but no video signal is present at all.

Answered! View the answer I have this problem too

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Can you connect an external display to see if the display its self is the issue or the GPU now that you got a video signal.

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While the cable looks OK, the image of the board connector was not at the needed angle to see the internal contacts as well as not sharp enough to tell to much. For now lets try the external with the cable disconnected.

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This system has a Radeon HD 6750M video card with 512MB of dedicated GDDR5 RAM. I don't know of any recalls on the 21.5" model. There was on the 27". Here's the Apple T/N iMac (27-inch): AMD Radeon 6970M Video Card Replacement Program.

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I checked if any recall exitsts but I only found for 27in model. Yes my GPU card is AMD Radeon 6750M. To be precise model is AMD 109-C29557-00.

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If the both the internal & external displays don't show any life and the external is correctly connected. I would say the internal display cable was put in backwards.

The diagnostic LED #3 is telling us the logic board & the graphics card are communicating so I don't understand it being off when you have the internal display disconnected. As the LED #4 is not lit that would imply the internal display can't be seen.

Yet you also tell us you can't get an image on the external. So you may have bad graphics board here as well.

Take a clear set of pictures of the cables end and the boards connector so we can see what we have here and post them in your question.

Update (09/19/2015)

At this point I think you'll need to replace the graphics card.

Here's the Apple P/N: 661-5944 AMD Radeon HD 6750M w/512MB

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Hello Dan

Thanks a lot for your attention.

I would just like to make a note about what you said: led n. 3 is on when the internal display is disconnected and is off when the internal display is connected. It seems to me like something is short circuiting the led.

I will post some images of the display cable endings as soon as possible.

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2011 GPU recall? Please give us the last four figures of your serial number located on the bottom of your stand

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I purchased a regenerated GPU from PCPartsOhio and I tested it with no success. While with my old GPU I got 3 LEDs on, with new GPU the system does not power on: when I push the start button LED 1 turns off.

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Sounds like you got a bad part. Try a different unit

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Hi,

I am Mustafa from Mumbai. I also have a-1311. In my machine cpu is heating normally , even the Gpu heats ok. Fan is rotating but there is no display. The main thing I observed is only one light is ie:1st led is glowing. non other led glows. If I am not mistaken, cpu and gpu heats up normally at least 3 led's should glow. pls suggest

Thanks

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raffaelecolella will be eternally grateful.
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