Getting Target Display Mode to Function on Late 2009 iMac

[Bikibuu]

Any help with this one would be appreciated.

At work we have an old iMac 27" (Late 2009, identifier iMac 11,1) that we have replaced with a MacBook Pro (2018, identifier MacBookPro 15,2). We want to use the old iMac as a monitor, and theoretically it should work since the Late 2009 to 2014 iMacs supported Target Display Mode. I've got a Thunderbolt (USB-C) to MiniDisplayPort adapter on the MacBook run directly into a MiniDisplayPort cable plugged directly into the old iMac, hit Command-F2, and nothing happens.

The iMac is running 10.10.5, the MacBook Pro is running 10.15.2 (Beta), so all the software versions are above 10.6.1. I've used this Apple Support document as a guide (https://support.apple.com/en-us/HT204592), but I can't seem to get it to work, so I'm clearly missing something. Any advice?

 

[chabig]

Confirm that the MacBook is logged in.
Confirm that you're hitting cmd-F2 on the iMac.
If still nothing, try hitting cmd-Fn-F2 on the iMac.

 

[Bikibuu]

Done, done and done. No success.
Watched a YouTube video in the meantime trying to see if there's anything I missed, the cable I use is a Mini DisplayPort cable from MicroCenter, not an Apple Thunderbolt cable as the gentleman making the video uses, would that be the issue? Are the pins in Mini DisplayPort and Thunderbolt different somehow?

 

[chabig]

Your cable should work. Try reseating the plugs, rebooting the machines, different ports.

By the way, your first post was nicely detailed.

 

[Bikibuu]

Thanks, I try to be thorough, usually you get better results in tech support if you know all the pertinent details and don't have to spend a lot of time tracking those down.

Reseated the plugs, rebooted both machines, tried different ports (on the MacBook, the iMac only has one DisplayPort port), so far, no avail. I wasn't logged into iCloud on the iMac, so I tried logging in there, thinking maybe it was like how Sidecar requires both the iPad and the Mac to be logged into the same account, no success, now the old iMac (despite successfully being logged in) keeps bugging me to type in my password, and never bringing up the 6-Digit code field to type in the authorization (everything shows up just fine on my iPad / MacBook for two way authorization) is it possible there's some operating system corruption on the old iMac or something that's not allowing this to happen?

Are there any other ways to activate Target Display Mode for the old iMac, a System Preferences option, a Terminal command or anything?

 

[chabig]

I can’t think of any reason the troubleshooting steps in the support document should not work other than the adapter or cable.

 

[Bikibuu]

Update - I switched out the cable for an Apple official one, no avail. Should I try to switch out the adapter?

A thought I just had was to run the System Profiler and see if the adapter shows up. I don't think it is, but most of my experience with doing this kinda thing was on an old 2006 Mac Pro tower, so, for example given, I don't know if Apple treats the USB-C ports as USB or Thunderbolt in the profiler. I've taken some screenshots, hopefully they can help with this.

This and the middle "USB 3.1 Bus" listing are identical, except for the bus number being 0x00 on the second.

This one is different but I confess I can't make heads or tails of it, or the previous ones really, I'm a graphic designer Jim, not a Hexidecimal Serial Hardware Reader.... Guy. Unlike other Macs I'm not seeing anything plugged into them, which, at the time of taking these screenshots the only thing I plugged in was the thunderbolt adapter for testing purposes.

The Thunderbolt ports look much the same way, where there's no device connected.

Ultimately this makes me think I got a bad adapter, but before I run back and forth to the store again I just want to make sure I'm looking at the correct logical ports - this adapter SHOULD show up in either the Thunderbolt or the USB listings, right? It wouldn't show in any of the other hardware listings, should it?

Also again thank you for all the help with this.

 

[Bikibuu]

I know this topic is pretty much old and dead, but, I came back to report upon it with some updates I found, for anyone else who may run into this in the future.

Apple updated their Target Display Mode Support file on December 17th 2019, adding a bunch of new information, most of which is pertaining to the various operating system permutations that Target Display Mode functions on, including now that it will not work on OSX Mojave (10.14) and later, and then archived the support file, effectively being done with the matter.

Use your iMac as a display with target display mode - Apple Support

Target display mode is a feature available with certain older Mac models.

support.apple.com

In my case, while the iMac is only on 10.10.5, the MacBook Pro I'm using is fully updated to Catalina. The document mostly talks about the specifics the iMac needs to meet, not the other computer, so while there's nothing in Apple's support file specifically stating that this shouldn't work, my suspicions are that the modern OS on the laptop is the trouble. Seeing as the iMac is no longer supported and the support file is archived, I guess this is more or less the end of this (unless someone else has some wild idea to test) and my solution is to simply buy a large monitor to pair with the MacBook Pro.

 

[ApfelKuchen]

For what it's worth, I'm using Target Display Mode with Catalina.

While the article you references is archived, there's another resource that is quite active: https://support.apple.com/guide/mac-help/use-an-imac-as-a-display-mh30822/mac - macOS Users Guide. There are three, OS-specific versions of the article for High Sierra, Mojave, and Catalina. No mention there about lack of/withdrawn support for newer OSes.

While there's no explicit mention of what OS may be needed for the targeted iMac (your Late 2009), I do keep both Macs on the same OS (as the target machine does run Catalina). Your late 2009 could be upgraded to High Sierra. If there's not a specific reason to avoid that upgrade, it may be worth a try.

 

[Bikibuu]

At this point, not really, since the idea is to move forward as the laptop as the base unit and run the iMac as a monitor \ backup machine. Thanks for the information, I'll try a software update and see if that fixes things.

 

[kirbyrun]

I have no idea if this will help or not, but when I was researching Target Display Mode (been using a 2011 iMac as a second display successfully for a few years now), I seem to recall reading somewhere a note that suggested that if it wasn't working, make sure you use an actual Apple keyboard to hit the key combination.

I have no idea if that helps or makes a difference, but it's the only thing I have to contribute.

 

[Zortrium]

Trying this same thing today trying to get a 2009 27" iMac to work as a display for a 2018 MacBook Pro. iMac running High Sierra (most recent supported), MBP running Mojave, all Apple-original cables. Doesn't work and none of the suggested fixed (or any others I've tried) have worked. I agree that the best guess is that recent OS updates have broken it (this configuration, anyways).

 

[servenvolley]

I use my '09 iMac in target display all the time with a 2015 MBP that runs Catalina. I have no problems going into and out of target mode with the devices now but I could not do it for a while after I first downloaded Catalina a few months back. I don't know what changed to make it work now.

 

[r6mile]

And yet TDM works well using a PC on a 2010 iMac, with a USB-C->mDP cable. I don't have a mDP-mDP cable to try with my 2013 MBA running Catalina, otherwise would be very interesting if it doesn't work!

 

[moraglen]

So it is August 2020 and yes there are still people looking for how to get target display mode to work.
And I am happy to report that Kirbyrun's post about having to use an APPLE keyboard was right on the money!! I normally use a microsoft keyboard so it was not working. Switched to an apple keyboard and it worked!!

setup;
target: late 2009 iMac 27/High Sierra,
source: late 2013 imac 27/Catalina
cable: cheap one from amazon

Thanks to everyone!!