External display occasionally shows just noise When I'm at work I have my Macbook Air mid-2013 hooked up to a Samsung SyncMaster 2443 display via a ThunderBolt-to-HDMI adapter and then to a HDMI-to-DVI adapter.

Almost every second time I switch the display on, the display is just noise. The resolution is correctly detected but the display is like this:



If this happened only when I first connect the display, it would be no problem, but it happens almost every time I lock my mac, and I have to power cycle the display 2-3 times to fix it.

Note that this behaviour has been present since Maverics, it's not new in Yosemite.

Is there a fix for this?
I have had the same problem with Maverick (in clamshell mode) / external monitor (Samsung SyncMaster 2443) when I lock my screen and use my bluetooth mouse or keyboard to wake up the computer.

I was able to fix the problem in 2 ways:

open the lid, login and unplu, replug the external monitor (pretty annoying)
when the multicolor static shows, press CTRL+SHIFT+Eject as if to lock the computer again, then wake up the computer again and I now have the normal login screen as normal (not ideal but less disruptive solution).

I hope this helps !