Q: Thunderbolt Monitors no longer work on Macs
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Mar 5, 2016 5:52 PMby Kappy,Astonishing that you cannot figure this out.
Install or Reinstall OS X from Scratch
Be sure you have backed up your files because the following procedure will remove everything from the hard drive.
Boot to the Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears.
Erase the hard drive:
1. Select Disk Utility from the main menu and click on the Continue button.
2. When the recovery menu appears select Disk Utility and press the Continue button.
3. After Disk Utility loads select the indented Macintosh HD entry from the the left side
list. Click on the Erase tab in the toolbar.. Set the Format Type to Mac OS Extended,
ournaled from the dropdown menu. Click on the Erase button. Wait until the operation
completes, then quit Disk Utility and return to the main menu.
4. Reinstall OS X: Select Reinstall OS X and click on the Install button.
Note: You will need an active Internet connection. I suggest using Ethernet if possible
because it is three times faster than wireless.
This should install the version of OS X that you had installed.
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Mar 5, 2016 6:08 PMby Rob F,Thanks for the reply.
I actually did a fresh install of Yosemite today. I copied the installer to an external drive, used Disk Utility to Erase the Hard drive on my MacBook to get rid of El Cap, then did the fresh install of Yosemite.
I figured that would do the trick. Won't following the procedure you described above leave me in the same place I'm in now?
Thanks again!
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Mar 5, 2016 6:14 PMby Kappy,Only if you have Yosemite installed. As it states at the end the process should install the version of OS X you had installed. This is because you do this using the Recovery HD that was created when you installed OS X.
Did installing Yosemite from scratch fix your problem? If you have a pristine installation of Yosemite that works with your monitors, then try upgrading it to El Capitan before installing anything else. See if El Capitan works with your monitors. If it does, then your problem was due to something you installed separately or something that has become corrupted.
If the monitors still don't work, then you ought to have them checked out.
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Mar 5, 2016 6:24 PMby Rob F,I had Yosemite installed, but upgraded to El Cap when it was released - that's when my trouble started.
I finally got around to doing a clean install of Yosemite today, hoping that would fix the problem. However, it's still not working.
There is no way I'm going to back to El Cap! I wish I had never installed it! Both Thunderbolt Displays worked on both of my Macs before I went to El Cap.
So, as it stands now on my MacBook, I have the fresh install of Yosemite, but neither monitor works with it. Both monitors work on the mini, but only one at a time - I can no longer use them together as dual displays.
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Mar 5, 2016 6:41 PMby Rob F,My MackBook is mid 2009, the mini is late 2009. They both came with a version of OS X that was pre Yosemite. I upgraded both to Yosemite ages ago, and both monitors worked with both Macs: I could use either as an external monitor on the MacBook, and both as dual monitors on the mini.
Then, when El Cap came out, I upgraded both Macs to El Cap. Since then, neither monitor has worked as an external monitor on the MacBook, and I can only use one monitor on the mini. I can swap between monitors on the mini, so I know they both work, cables/connectors and all.
This morning, I decided to get rid of El Cap on the MacBook, and did a fresh install of Yosemite on the MacBook only. Neither Thunderbolt Display works with the MacBook - I even unplugged the one that I had connected to the mini, so I know for certain it was working. It didn't work with the MacBook, but worked with the mini when I reconnected it.
I can use an Acer monitor as an external on the MacBook, so I know the display port is working.
I just can't get the Apple monitor to work with the Apple computer, which used to work before I installed El Cap.
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Mar 5, 2016 6:49 PMby Kappy,Given the situation I have no answer for you beyond what I've offered. If the computers worked with the monitors and Yosemite worked with the monitors, but now they don't then logically the monitors or how they are connected or the cables involved are the logical suspects.
