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27" imac 2011 screen doesn't turn on but it still works

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Hi everyone,

I have a 27 inch imac 3.4ghz from 2011 and its been working great until a few weeks ago. Everything on it works fine except for the fact that the screen turns on for about 10 seconds when the machine is powered but then switches off. I have connected the mac to another monitor and its been working great without any issues. Sometimes the screen turns on randomly after the mac has been on for hours and then goes off after a few minutes :(

I'm basically here just to ask if this issue is caused by the GPU (AMD Radeon HD 6970M 2GB) being faulty or if its something else and was wondering if anyone could possibly help me?

Thanks :)
 

Raz0rEdge

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GPU failures might cause this, but usually that manifests itself with graphical glitches that continually get worse over time. A total failure is more indicative of a LCD or backlight failure. If the machine works with an external monitor plugged in, that might be the route you should go with until you decide it's time to upgrade.
 

pigoo3

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If this iMac has been moved around a bunch (or maybe just experienced one hard bump/jolt)...maybe a cable has gotten loose.

I'm also thinking if there was a GPU failure...it would effect the external monitor as well.

The most likely cause is as Raz0rEdge mentioned...maybe a component related to the display may be failing.

- Nick
 
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Thank you both for the replies.

GPU failures might cause this, but usually that manifests itself with graphical glitches that continually get worse over time. A total failure is more indicative of a LCD or backlight failure. If the machine works with an external monitor plugged in, that might be the route you should go with until you decide it's time to upgrade.
Hmmm. I kept thinking it was the gpu and planned on buying a second hand one and replacing it but from what you're saying the LCD or backlight might be the culprit.

If this iMac has been moved around a bunch (or maybe just experienced one hard bump/jolt)...maybe a cable has gotten loose.

I'm also thinking if there was a GPU failure...it would effect the external monitor as well.

The most likely cause is as Raz0rEdge mentioned...maybe a component related to the display may be failing.

- Nick
We did actually have a power cut a week before I got this issue so maybe that might have caused it? I do get glitches but it only appears on the imac screen when the screen turns on randomly. I've never experienced any glitches on the external monitor.
 

pigoo3

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Hmmm. I kept thinking it was the gpu and planned on buying a second hand one and replacing it but from what you're saying the LCD or backlight might be the culprit.
I do not believe the GPU in a 2011 27" iMac is "easily" replaceable. The GPU in a 2011 27" iMac is the Radeon HD 6970M...with the "M" standing for mobile or mobility. This basically means it's laptop style GPU...not a separate & replaceable GPU card like you might expect in a tower desktop computer. It's still a pretty powerful GPU (for it's time)...but it may be surfaced soldered to the logic board...and not easily replaceable. More likely the way to "replace" a 27" 2011 iMac GPU would be to replace the logic board with a known working logic board (which is usually a pretty expensive endeavor).

But...this may not be important...since if the GPU was failing...you would probably have issues with both the built-in display & the external display (since they both use the same GPU).

We did actually have a power cut a week before I got this issue so maybe that might have caused it? I do get glitches but it only appears on the imac screen when the screen turns on randomly. I've never experienced any glitches on the external monitor.
The power loss you experienced is always a possibility (since power spikes of any sort can be unpredictable)...but I'm thinking if this was a "normal" power loss (not associated with strong lightening or storms)...that it may not be the cause. The more likely cause could be a loose cable...or even more likely a display related component that's failing.

- Nick
 
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Every 6970M GPU failure I've seen has effected both the iMac's display and external video. The GPU is a BGA surface mount device soldered to the video card PCB, and the video card is socketed to the rear of the logic board. If there was a backlight issue, the image should faintly be seen on a clean screen, and better with a torch shone on the screen. Likely an LCD fault, I have seen similar symptoms as described by the OP. Part no longer available from Apple now as it's a vintage product. Buying used you can never be sure of quality. Many display's now suffer from serious dust ingress, looking like cloudy sky's, others may be dim.
 
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Yes, I have the same issue and it has been working fine for a long time. Until it was moved heavily for last few weeks. I don't know if it was dropped by the mover.
 
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