Couldn't help chuckling after reading that: it happens to be what I said, word for word, to a Genius Bar guy after he informed me that my iMac wouldn't be fixed under Apple's recall program and as I was arguing that the problem occurred not from misuse, as he suggested, but from a latent fault in the GPU that is bound to manifest itself sooner or later in any model with the 6970.
The irony of this is that those who spent less money on a 2011 model probably still have them running today, while those who actually spent more and went with the highest-priced models with the 6970, had them fail.
So you end up having been more profitable to the company and not having anything to show for now.
While I don't repair Macs for a living like you do, allow me to chime in as someone who spent a good few months trying to do the same thing, and say that you're in for a true time-sink. No combination of MXM GPUs, flashed BIOS, display drivers and/or OS versions that I tried yielded anywhere near the same functionality/stability that the stock one did.
From my own personal experience trying to make my 2011 iMac simply usable again, as well as everything that I've learned from having read every single one of the 694 posts in this thread as well as feedback gotten from chatting with other users who did the same, I'm now convinced that, if you own a 2011 iMac with a failed 6970, you can summarise your options to the following:
- if you want your iMac to perform exactly the same way as it did before its 6970 failed, you'll have to resign to parting with whatever money Apple charges (over £300, in my case) to fix it themselves. I believe this is the only way that you can get a new 6970 in your system, with some sort of warranty (1 year, I believe?).
I can't possibly consider this a valid solution since, as @rivermandan pointed out, this GPU is a ticking time bomb. It has a design flaw that will manifest itself sooner or later. You can be lucky, and have it develop while under warranty and have Apple replace it for free. But, more likely, it will happen after that first year, and you'll be back to square one after having wasted a tremendous amount of money.
- if you want your iMac to perform exactly the same way as it did before its 6970 failed, but you can't afford or don't want to spend the amount of money Apple charges for a new 6970, you can buy a used one for about one third of the price.
This is even less of a valid option since, as I pointed out, a used one is even likelier to fail (and will fail). As if that isn't enough of a deterrent, they're rare and hard to find.
- if you want your iMac to perform exactly the same way as it did before its 6970 failed, but can't afford to spend a huge amount of money trying to solve this, you can try to have it reflowed like @T'hain Esh Kelch kindly reminded me. Last time I checked in the UK this should cost around one sixth of what Apple charges for a new one, but you have no guarantees that it will work. Even when it does, it is a matter of time until the GPU fails again, determining factors being how much you push it and the quality of the job. I understand that, if you're lucky, you might find someone who will only charge you on a successful reflow (don't quote me on this).
Also, if you have the guts/knowledge, you can always try to do the reflow yourself, with the obvious advantage that this won't cost you anything and you might as well try to get something out of an otherwise useless component.
- if you're willing to part with or don't need certain functionalities, such as the boot screen and native brightness control, you can buy an MXM GPU pulled from a non-Apple system. You'll have to rely on reports by other users who successfully took this route to determine which cards are compatible. Not only will you have to search for a certain model, you'll also need to find specific brands and BIOS versions. Any mismatch in those combinations will make it unusable in your iMac. As a consequence, finding one of these cards takes a considerable amount of time.
You may have to perform physical modifications on your heatsink as some cards won't fit in it as the 6970 does.
This does have the benefit of giving you a performance boost, provided the card you buy is more powerful than the 6970.
I have to reinforce that this is only a valid option if you are positive you are happy to part with the boot screen and brightness control. From my experience, depending on which card you get, your system will also likely be less stable than it was with the stock GPU, with the occasional crash, freeze or boot into a white or black screen.
Any macOS update comes with the risk that it may stop working with the card.
If you use BootCamp, it may also not work with Windows. Even when it does, finding working drivers for it may be hard or even impossible (in which case, you do have the option of modding them yourself, at least). I noticed that in Windows (couldn't find out on macOS), some cards, such as the 780M, have their clock speeds locked and won't run at full performance. Even manually editing and flashing a BIOS, making sure the clocks were unlocked and maxed out, didn't work, in my case.
Having taken this route, I was surprised to find out that I couldn't cope with the loss of brightness. Apparently, some people are less sensitive to this than others. No brightness control app that I've tried managed to have the same effect that the native one did with the stock GPU, simply because they don't control the brightness at all: they simply apply some sort of filter that tints the screen darker or lighter. Actual brightness never really changes. This is easy to observe on a dark room. I found that this makes the image dull and couldn't cope with it. You may not be as sensitive to this.
- if you can't afford to lose functionality but are happy to lose performance, you can buy a used GPU pulled from a pre-2011 iMac. I haven't tried this route personally, so I can't vouch for it, but it should work: the OS should have native drivers for it, boot screen and brightness control should remain functional and everything else should work as it did with the 6970, with the obvious performance loss, as all pre-2011 iMac GPUs are less powerful than it.
This option still has the drawback that you can't buy a new GPU. They're simply not available. Any listing describing them as new is either inaccurate or false. You're forced into buying a used one, pulled from an older iMac. It will always be a gamble, as you can't tell how the previous owner used it; how much stress it has been through. It can fail, albeit at a much lesser rate than a 6970, considering both cards have been given similar usages. Also, as if this wasn't enough, I've also read reports that other GPUs used on pre-2011 iMacs are also prone to failing, with similar symptoms to the 6970, so there will always be some risk associated to this route.
All in all, if performance is important to you, then this isn't a valid option at all, since the drop from a 6970 to any pre-2011 iMac GPU is very noticeable.
If you, however, just need your iMac to be usable again and the performance loss won't matter, I'm convinced this is still the best option available to you.
I would still love to hear from any owner who took this route and report on his experience.
- I'm only going to mention this possibility for the sake of accuracy, but it really isn't worthwhile due to their obscene price right now, but an external GPU would also bring the iMac back to life. You won't, if what I've researched is correct, get image from its internal display, so you would be limited to external ones anyway, which further diminishes this option's viability.
- I have also unsuccessfully attempted a seventh option, which was to disable the iMac's discrete GPU by deleting its driver files and try to make it work with the GPU that's integrated in Intel's CPUs. This is way beyond my comprehension, and I can only imagine that the integrated GPU is either disabled or unaccessible, and I was never able to pull it off. This was done by following the same instructions for disabling the discrete GPU on MacBook Pros and using their integrated ones: https://web.archive.org/web/2017020....edu/~zc227/extras/early2011mbp_graphics.html
Even if this worked, you should expect the system to function with a severely limited performance.
It would, however, be a feasible option if you simply couldn't afford to spend any money at all but still needed to access your iMac.
-off-topic: after several months of compulsively trying to get my 2011 iMac to work again, I ended up, by chance, buying a 2014 iMac with a broken (but working) retina display, which I intended to repair and sell for a profit. Having disassembled and reassembled my old iMac so many times had the perk of allowing me to take these things apart with my eyes closed, now. It cost me only slightly more than any MXM GPU card I had bought before to replace the 6970 and, ironically, I ended up keeping this system for me. This whole process of trying to bring my then beloved 2011 iMac to life just wore me down to a point where I simply considered the resources invested (wasted) in it to be higher than the loss of an item that cost me over £2,000 less than 4 years before.
Again: these are just my thoughts based purely on personal experience and may not be 100% accurate. Others may have different conclusions based on their success (or lack of) stories. Feel free to correct me or offer any suggestions on where I may be wrong.
Good luck and lots of patience!
