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Target display mode not working?

J

joeriggs

macrumors member
Original poster
I have a 2012 IMac on Sierra and a 2019 Intel Macbook pro on Monterey 12.3.

I've connected the two via thunderbolt - Imac - Thunderbolt 2 cable - thunderbolt 3 to 2 adapter - MacBook Pro

I press command F2 on Imac and nothing happens. Any ideas?

Thanks
 
joeriggs said:
My Imac is 2012
Click to expand...
You have the 27 inch iMac 2012? You are using the Apple Thunderbolt 3 to Thunderbolt 2 cable? Can each Mac see the other Mac in the Thunderbolt tab of System Information.app?

Thunderbolt Target Display Mode (TTDM) still works for me to a iMac (27-inch, Late 2013) running Monterey 12.4 (with OCLP). The other Mac is a Mac mini 2018 also running Monterey 12.4.
https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/post-31109030

When I press Command F2, nothing happens if my Sonnet Echo Express III-D containing a PCIe serial port card is connected. If I disconnect that, or boot with the Mac mini already connected, then TTDM works (but the serial port card doesn't?).

If the screen goes black, then you know it's doing something. Sometimes I need to press Command-F2 a couple times to make the screen not black. Another option may be to use the Enable Display option in SwitchResX. Usually I need to press Command-F2 a couple times to stop TTDM.

Older Thunderbolt iMacs may have different behaviour?
https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/post-31109756

Did you try booting with no other Thunderbolt devices connected? Booting with the Macs already connected?
 
joevt said:
You have the 27 inch iMac 2012? You are using the Apple Thunderbolt 3 to Thunderbolt 2 cable? Can each Mac see the other Mac in the Thunderbolt tab of System Information.app?

Thunderbolt Target Display Mode (TTDM) still works for me to a iMac (27-inch, Late 2013) running Monterey 12.4 (with OCLP). The other Mac is a Mac mini 2018 also running Monterey 12.4.
https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/post-31109030

When I press Command F2, nothing happens if my Sonnet Echo Express III-D containing a PCIe serial port card is connected. If I disconnect that, or boot with the Mac mini already connected, then TTDM works (but the serial port card doesn't?).

If the screen goes black, then you know it's doing something. Sometimes I need to press Command-F2 a couple times to make the screen not black. Another option may be to use the Enable Display option in SwitchResX. Usually I need to press Command-F2 a couple times to stop TTDM.

Older Thunderbolt iMacs may have different behaviour?
https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/post-31109756

Did you try booting with no other Thunderbolt devices connected? Booting with the Macs already connected?
Click to expand...

Yes, each mac sees each other under the Thunderbolt tab in System Info.

Both Macs have to be on Monterey though right? It won't work with one on Monterey and one on Sierra?
 
Last edited:
joeriggs said:
Both Macs have to be on Monterey though right? It won't work with one on Monterey and one on Sierra?
Click to expand...
I don't think the Thunderbolt Target Display Mode protocol has changed since it was created.

I booted the iMac 2013 into High Sierra while the Mac mini 2018 is running Monterey. Target Display Mode was enabled immediately upon pressing Command-F2
on the iMac. The iMac appears as a display connected to the Intel UHD Graphics 630 GPU. 2560x1440. AllRez says all the iMac modes are 10bpc RGB SDR.
 
Last edited:
joevt said:
booted the iMac 2013 into High Sierra while the Mac mini 2018 is running Monterey. Target Display Mode was enabled immediately upon pressing Command-F2
on the iMac.
Click to expand...
This gives me hope, do I need to have OCLP installed on the Monterey machine?

To reiterate, I have a late 2012 IMac on Sierra and a 2019 16" Intel Macbook Pro now on Monterey 12.4
and so far Command-F2 is not working.

I don't want to upgrade the OS on my Imac and I would prefer to not have to downgrade to Catalina on my MBP as I would lose functionality on my TB4 dock.
 
Last edited:
I can boot my Mac mini 2018 to Monterey and iMac 2013 to High Sierra, both without OCLP, and still get Thunderbolt Target Display Mode.

You could try installing a new OS to the iMac - keep the old OS. Put the new OS on a new partition or disk.

Did you try without the TB4 dock or any other Thunderbolt device connected?

Does nothing happen when you press Command-F2 on the iMac? There should be some Thunderbolt related messages in the log.
 
joevt said:
Did you try without the TB4 dock or any other Thunderbolt device connected?

Does nothing happen when you press Command-F2 on the iMac? There should be some Thunderbolt related messages in the log.
Click to expand...

Yes, I tried without anything else connected to the computers just keyboard on the Imac, also tried with both devices already connected via thunderbolt cable and adapter and restarting the Imac. Unfortunately nothing w/ Command-F2.

Interestingly enough connecting the Imac via a mini displayport to hdmi cable to hdmi to Usb-C adapter, resulted in a flash of a black screen when pressing Command-F2 but that's it.
 
For now I think I'm unfortunately resigned to using a software app to enable my Imac to be seen as an airplay display on my MPB.

But now of course neither of my DVI monitors (DVI to HDMI) will connect to my Intel MBP now (12.4), I've tried HDMI to Displayport to Caldigit TS3 dock, I've tried HDMI to USB-C, I just get blank screens.

This is driving me insane and stuff like this is ridiculous with Macs.
 
Last edited:
Hi all, I had all sorts of problems with target display mode, but SOLVED my issue with a bit of persistence. What I learnt that affected my connection was both 1. Keyboard, and 2. Screen Brightness.

1. I have come across forum posts of prior dates indicating other users switching to non apple keyboards having issues with activating Command F2. I just happened to have moved from proprietary Mac keyboard to Logitech, when Target Display Mode stopped working for me and this led me to explore a solution. Plugging in another keyboard that was non Mac didn't solve the problem. And through Logitech keystroke tracking I new I was actually pressing Command and F2. It turns out that I needed to set Show Input Device relating to keyboards to show on the top bar menu, and then I needed to have the virtual keyboard displayed. From there, double pressing the command button to lock it in as active and then pressure fn/F2 depending upon what shows up on your virtual keyboard did the trick. To disconnect, just pull out one end of the cable (I'm using thunderbolt). So it seems like Command F2 doesn't activate non Logitech MX keyboard, but thankfully the apple Virtual onscreen keyboard doese.

2. Sometimes I get a black screen where my macbook can see the imac, but the imac screen is still black. I solved this by turning my imac screen brightness upp a couple of bars, or just to toggle it and this did the trick for me.

Hope that helps somebody!

I'm connecting Big Sur Macbook Pro to 2013 iMac running Big Sur
 
2014 running Big Sur.

Another golden tip is that I’ve found some programs interfere with TDM activating, also leading to black screen. It’s best to close all programs before trying to activate.
 
joevt said:
I can boot my Mac mini 2018 to Monterey and iMac 2013 to High Sierra, both without OCLP, and still get Thunderbolt Target Display Mode.

You could try installing a new OS to the iMac - keep the old OS. Put the new OS on a new partition or disk.

Did you try without the TB4 dock or any other Thunderbolt device connected?

Does nothing happen when you press Command-F2 on the iMac? There should be some Thunderbolt related messages in the log.
Click to expand...
I have a iMac 21.5 late 2012 on macOS Catalina 10.15.7

and a MacBook Air M1 on Ventura 13.5.2

And I try to use my iMac as an external monitor by target display mode.

I've connected them via thunderbolt: iMac - thunderbolt 2 cable - thunderbolt 3 to 2 adapter - MacBook

I press command+F2 on iMac and nothing happens. I press Fn+command+F2 on iMacand nothing happens.

Or rather my iMac makes a beep. I had check success connection in system information.app. Each Mac see the other Mac in the Thunderbolt tab of System Information.app. I have press command+F2 and Fn+command+F2 but nothing still works.

Thanks.
 
slavadarkk said:
I have a iMac 21.5 late 2012 on macOS Catalina 10.15.7

and a MacBook Air M1 on Ventura 13.5.2

And I try to use my iMac as an external monitor by target display mode.

I've connected them via thunderbolt: iMac - thunderbolt 2 cable - thunderbolt 3 to 2 adapter - MacBook

I press command+F2 on iMac and nothing happens. I press Fn+command+F2 on iMacand nothing happens.

Or rather my iMac makes a beep. I had check success connection in system information.app. Each Mac see the other Mac in the Thunderbolt tab of System Information.app. I have press command+F2 and Fn+command+F2 but nothing still works.
Click to expand...
Catalina is problematic. Later macOS versions switch to Thunderbolt Target Display Mode easier (except Ventura may have some flickering). However, if you also want audio, then I think High Sierra is best but I haven't tried Mojave.
https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/post-32431118
 
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