HOWTO set up 27" iMac for permanent Target Display Mode?
It appears the display and/or logic board for my iMac has achieved terminal failure. This is not my screen, but the display exhibits these same symptoms.
The display is blocky and degraded even after wiping the HDD and installing fresh OSes (Yosemite through High Sierra) and when booting into the Utilities menu from an installation USB stick, as well as in screen sharing from remote desktop. Didn’t think it would happen there, but it does. It works flawlessly in target display mode, however, so I’m pretty sure the internals are roasted. As of May 2019, used Radeon 5750/6970 display cards are not cost effective to replace, so on to Plan B.
I had been using the iMac in Target Display Mode exclusively, but even in TDM, having booted to a login screen on a vanilla system install, the fans constantly kick out processor heat. Not full-bore fan blast, but more than I’d expect for what should be idle load on the procs. It’s noisy and heats up the room, and I know it’s drawing more power than needed just to light the screen so on to Plan C.
I got Apple’s shipping label for their free recycling program and am about to send the iMac to be shredded or whatever they do, but I need to open it to pull the HDD before packing it up.
It occurred to me that while I’m in there I have an opportunity to disconnect any or all components not critical to target display mode, essentially up-cycling the iMac as a dedicated monitor.
So here’s the question.
Anyone know how target display mode works on the hardware/firmware level? Target display switches on instantly once a cord/signal is detected. A keypress is not required, nor does it need to switch over from the OS, so it does not appear to rely on software. Knowing nothing, I would think pulling the HDD, CPUs (if not soldered on) and disconnecting the fans should effectively make it a full-time monitor, but then again maybe not.
This model has been around nearly ten years, and since there’s always someone on the internet who has already done what you’re about to do, I’m putting it out there: Who knows the what the deal is with target display mode? And is what I’m trying to do even possible?