Troubleshooting tips for using an old imac as an external display
Old imacs never die—their screens just fade away. But you can use them in the meantime!
Because of the decreasing value of older computers and the reality that sometimes children depart the nest and leave their old computers behind, you could wind up with an older imac that no longer meets your day-to-day needs but that you could transform into a monitor.
All the imac models that can work in what Apple called Target Display Mode as a
secondary display for a modern Mac require an adapter to connect a Thunderbolt 3 port on the imac to a Mini Displayport or Thunderbolt 2 port on the older imac and have things function as expected.
imacs released from late 2009 through mid-2014 can be used as external displays. Those that followed, starting with the 27-inch 5K late-2014 edition, cannot. (You’ll find a bit more information about this at this archived page on Apple’s support site [fave.co/3ubn6qr].)
ADAPTERS
For the 2009 and 2010 imac models with Mini Displayport, purchase a USB-C to Mini Displayport adapter. Fortunately, because the imac has a jack into which you plug a cable, this is not nearly as difficult as driving an Apple display that only has a plug on the end.
A number of sub-$20 Mini Displayport to USB-C adapters are readily available, such as the model from Allsmartlife (fave. co/2pdselh). Some USB-C docks also include Mini Displayport support. You also need a Mini Displayport to Mini Displayport cable, which costs under $10.
For the 2011 to 2014 Thunderbolt 2 imacs, you need a Thunderbolt 2 to Thunderbolt 3 adapter (Apple’s is $49 [fave.co/3uljfiy] or you can buy a thirdparty one), and a Thunderbolt 2 to Thunderbolt 2 cable (fave.co/39jheyu), which can cost $20 to $30. Even though Thunderbolt 2 and Mini Displayport connectors appear identical, the wiring is not the same and a different cable is required. Make sure you are purchasing a cable with a lightning-bolt icon on both ends that has a rectangular connector— not the rounded USB-C one, which is used for Thunderbolt 3.
MAKING THE CONNECTION
With the right cable in hand and your two machines connected, started up, and running past the Filevault login screen (if enabled), your Thunderbolt 3–equipped Mac should simply recognize the imac as a target display and the imac’s speakers should appear in the Sound preference pane as an audio target. Other interface ports and the imac’s camera aren’t available to use.
If that doesn’t happen, press Command-f2 on the keyboard connected to the imac you want to use as a display. On a laptop or a keyboard that doubles function and other keys, press Commandfunction-f2.
Some people have found they needed to log out of the active account on their older imac and use Command-f2 at the account login screen. Failing that, you can try resetting the PRAM/NVRAM on both computers (fave.co/2r3sdm9), which often clears up display-recognition issues. ■