Questions about Reviving iMac 2012 — Target Display Mode, Luna Display Unit, Bootcamp

[Dahlia]

I have a late 2012 iMac, model A1419, with a dead hard drive. Apparently, this 2012 model can be used as a Target Display in certain situations, but probably not mine! My working iMac is a 2020 iMac, model A2115. It seems that I could spend quite a bit of money just to find out that my 2020 + 2012 in Target Display Mode configuration will not work. I am looking for advice on options for this 2012 machine.

• Can I use this 2012 iMac as a Target Display for my 2020 iMac? From my research, I think the answer is NO because Apple removed this feature from my 2020 iMac.
• If I am wrong and I CAN use the 2012 iMac as a Target Display, the 2012 iMac needs a new hard drive. I like my external Samsung T5 running Windows via Bootcamp on my 2020 iMac, and would get another one. (I am not capable of opening up the machine to replace the existing drive; I would have a breakdown.) Also, apparently the 2012 iMac can be in Target Display Mode only when running High Sierra 10.13.6 or earlier. The specification is unclear. Some people report no problems running Catalina; some people recommend installing the system that came with the machine. How do I find out what the original macOS was? I have no idea! I was running Catalina on this iMac when it died. (My 2020 iMac is running Catalina. I am not planning on upgrading to Big Sur any time soon.)
• If I CAN use the 2012 iMac as a Target Display with the 2020 iMac, and I get the new hard drive working, what kind of cables would I need to connect the two?
• If I CANNOT use the 2012 iMac as a Target Display, can I use a Luna Display Unit to connect it to the 2020 iMac? In this scenario I still need a functioning hard drive on the 2012 iMac.
• If all this is silly and a waste of money and time (hard drive, cables, Luna Display), can I use the 2012 iMac as a Bootcamp machine? (In this scenario I have no idea how to set up anything.)
• If all this is very silly, should I just get rid of the old iMac and buy a new monitor? And how do I get rid of an iMac where the hard drive is dead but intact?

Thank you!

 

[Fishrrman]

I don't believe a 2020 iMac can "send out" a signal for target display mode. I could be wrong.

If you are certain that it's only the hard drive inside the 2012 that has failed, why not connect an external drive (small USB3 SSD would work), and boot & run it that way?
Shouldn't be very hard to get going again.

 

[uller6]

I have a late 2013 iMac and I tried, without luck, to get target display mode running with a 13” 2020 intel mbp (Big Sur). I couldn’t get it to work using internal drive on 10.13.6, booting from an external ssd on 10.13.6, booting internally from Bug Sur (patched). I was using an Apple thunderbolt 2 cable with the Apple thunderbolt 2 to thunderbolt 3 adaptor dongle. I’m really bummed I couldn’t get it to work, and from what I read Apple removed the ability to send signals to a target display Mac in Big Sur. I haven’t tried using an older version of MacOS as the source, but I’m not about to roll back the OS on my machine just to see if I can get target display mode working.

this is really a shame because target display mode was so awesome. I hope Apple brings it back in the future!

 

[Nguyen Duc Hieu]

I would just sell the iMac 2012 and buy a stand-alone monitor. Maybe get enough money to buy a cheap 4k 27" monitor.
Save myself the hassle and all.
Remember that the TB3 to TB2 adapter + TB2 cable combo does cost some money, something about half the price of a 27in monitor.