I have the 27" mid-2011 iMac that was recalled due to an issue with its AMD 6970M card (1GB for me), but in my case it just malfunctioned after 6 years and it's out of warranty and not eligible for any free repair.

In this forum I got the details of how to connect it to a new 2017 MacBook Pro with Touchbar, using TB cable (older) and TB to USB-C adapter. That's all good.

Questions I have:

  1. Will Target Display Mode attempt to use the GPU of the old Mac or use my MBP's GPU?
  2. If I have to use a video card in the iMac, is there some other integrated graphics card on my iMac I can use and how do I disable the faulty AMD one? The AMD one sometimes (or rather most of the time) prevents the iMac from booting and sends it to an endless restart loop or hangs the machine in ever lasting suspension.
  3. Assuming we get past the two above, anyone know of any easy solution so that I don't have to boot the iMac all the way and then use keyboard shortcuts to enable TDM? I actually would like to connect the keyboard and mouse of the old iMac to the new MBP permanently.
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    Welcome to Ask Different! :) I'm just curious as to how handy/confident you are around a computer? You may be interested in taking a look at this answer and its associated comments if you'd in fact prefer to keep using the iMac as an iMac rather than a display. The iMac referred to in that answer is still working fine to this day. – Monomeeth Oct 5 '17 at 8:07
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    Thanks for the reply. It's been years since I performed surgery in desktops and that was in PCs. Certainly not comfortable performing this on iMac, as I've seen the videos; too complicated, extra cost to even get all the tools necessary and frankly not have the time. Plus would it ever be fixed for good? But regardless, very interesting solution! – user507866 Oct 5 '17 at 10:32
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    For No. 2 You might try apple.stackexchange.com/a/295805/251859 (This is in software & reversible) Will ensure boot and bypass AMD – Target Display Mode untested though. – LаngLаngС Oct 7 '17 at 8:23

Answers to your questions as asked are:

  1. I've seen your model iMacs used in Target Display Mode regardless of the fact the GPU is playing up, so from that perspective you'll be fine.
  2. N/A see 1 above.
  3. Getting past the first two is the easier part, it's getting the iMac to go into TDM that's going to be your issue as you really need to at least have it booted up to the login screen.

For more general info on TDM refer to: Use your iMac as a display with Target Display Mode.

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    Thanks for the reply. Your answer to 1) certainly gives me hope. But hesitant to pay for adapter and cable if I can't get it to boot. And sometimes it is really stubborn, it won't boot for ages, freezing or going into a loop. And sometimes the screen will produce the stripes just before login page. The Cmd+F2 might still work perhaps at that point but just very unreliable I would imagine. – user507866 Oct 5 '17 at 10:34
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    Agreed. If you're having trouble booting the iMac it's not going to be a reliable solution. Even if you left it powered up after a successful boot, it's not a long-term solution. As for the cable and adapter, I would imagine you could return these if you needed to, but it's probably not worth the hassle. If performing surgery isn't an option for you, then your best bet may be to sell it for parts. – Monomeeth Oct 5 '17 at 10:47

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