Why does connecting a Macbook Pro to a 2160p external monitor via Mini-DP result in a mess of green/purple colors? When I connect my Macbook Pro to a 3840x2160 external monitor, the external monitor keeps going black and readjusting every 1-2 seconds. Some times it stops briefly, but the screen is just filled with green and pursple-ish colors, with the text "Use 3840x2160@60Hz for best result". I managed to take some pictures at the short breaks between constant readjusting and the text "No input source".





I checked which resolution the Macbook was trying to use for the external display, and it seems to be correct:

$ system_profiler SPDisplaysDataType | grep Resolution
          Resolution: 2560 x 1600 Retina
          Resolution: 3840 x 2160 @ 60 Hz

I have used the 4K screen a lot with a different PC and I know it works. I have admittedly not used the Macbook with an external display before, because I don't have the ability.

I have rebooted the Macbook, restarted the screen, reconnected the Mini-DP cable many times and tried using both Thunderbolt ports.

Has anybody seen something like this before, and could venture a guess as to what's wrong?



I'm using a brand new Macbook Pro retina 13" from 2015. The following is copied from its spec-sheet:


2,7 GHz dual core Intel Core i5, Turbo Boost up to 3,1 GHz 
8 GB 1866 MHz LPDDR3 SDRAM
128 GB PCIe-based flash storage
Intel Iris Graphics 6100
First thing I'd try would be a different cable.

Apple has this to say about non-compliant Display Port cabling, though not specifically in response to your particular issue, but Google brought me there whilst on that search...


  Certain cables advertised as being VESA 1.1a compliant may contain a construction issue that may result in the DisplayPort power pins at either end of the cable shorting together. VESA 1.1a compliant cables must isolate the DisplayPort power pins at either end of the cable.
  To learn more about the VESA 1.1a DisplayPort Interoperability Guidelines, visit www.vesa.org