iMacs not working in Target Display Mode

[rboerner]

Originally Posted by Tomsjotun

Im trying to use my old iMacs (2009, 2013) as external screens to my MacBook Pro.

The 2009 works automatically but the 2013 wont work.

I have tried to switch cables between the two, but only the 2009 works.

Any ideas?

'Target Display Mode' does NOT use DisplayLink technology. As a result, DisplayLink will not be able to assist you.

That said, Apple has very specific requirements in order for Target Display Mode to work as they describe here --> https://support.apple.com/en-us/HT204592

If that information doesn't help, I would suggest contacting Apple directly for assistance.