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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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Progress bar gets halfway before the screen goes grey

I seem to be having an almost identical problem except I'm using a 2011 27" iMac.

What I find strange is that trying to boot from external drives with mac partitions result in the same behaviour: progress bar gets halfway before the screen goes grey.

I have tried the single user mode approach and the FSCK fy command but that doesn't seem to have sorted it either.

It seems as though I may just have to open the iMac up and replace the drive...

Answer this question I have this problem too

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1 Answer

Sadly, this symptom is a sign the dedicated GPU this system has had failed. Running under Safe mode will work as the Intel CPU graphics engine using the systems firmware graphics driver.

Your options are a bit limited as the availability of a replacement GPU board are. Now hard to find and most are used. The reason these GPU boards die is two fold, lack of cooling as the fans and heat sinks are jammed up with dust as well as deteriorated thermal paste and pads these boards need to keep cool. The second issue is this series was designed when we didn’t have these more advanced (heavy graphics apps) which are very demanding. So between poor cooling and running harder than what was expected this series is doomed!

That’s not to say it’s a bad system! On the contrary! As long as you give it the needed TLC and don’t play gaming or other ultra heavy graphics uses it’s just fine! I use mine for work processing and doing other boring stuff!

Some folks have managed to get a bit more life from their systems besides cleaning and fresh thermal paste & pads, is in fact cooking the board! There is two possible solutions why this works the GPU chip internal solder joints used a Tin solder which can develop Tin Whiskers! These strands can create shorts! The heating causes the filaments to recede. The other issue is the tantalum capacitors breakdown and can sometimes be revived by the heat.

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