Second HDMI just stopped working. Mavericks, GA-H67N, i7-3770K, HD 4000.

[hustlersquad]

I've been happily using both HDMI ports in Lion, then Mountain Lion, then Mavericks. One for my Dell monitor and one for a Panasonic TV. Now whichever display I connect to the "top" HDMI port (next to the VGA port) displays a black screen. The computer recognises that a second display is connected and the desktop adjusts (ie the working screen turns black briefly and the Dock repositions).

I can't think of anything I did that would have affected this. I had drama getting Mavericks up and running but RehabMan (of this awesome forum) rescued me and I was able to get everything working smoothly. I haven't updated anything since then so I'm pretty confused about why it would just stop working.

Before I screw everything up even further, what might be the logical steps to troubleshooting this issue Any help would be much appreciated!

Thanks

 

[toleda]

I haven't updated anything since then so I'm pretty confused about why it would just stop

7 Series processor on a 6 series motherboard.
Yosemite install; did you select MultiBeast/Drivers/Graphics/Intel Graphics Patch for Mixed Systems?

 

[hustlersquad]

I did select the mixed system patch. Everything was working fine since I installed Mavericks. Then one day it just stopped working. With both displays connected, System Preferences > Displays > Gather Windows shows that the Panasonic TV is recognised and I'm able to change the resolution etc. The problem is that nothing shows on the display. Same thing happens the other way around if I switch the HDMI ports. Both displays are recognised but only one works.