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before posting this question I just want you to know that I did a lot of googling and came up empty.

I'm on OS: Windows 7, GPU: ADM Radeon 5850 (using AMD Control Center, latest drivers installed). I have one LCD screen that I use for casual work on my PC and I also have Panasonic Viera, that I'd like to mirror my full screen gameplay to (for presentation purposes). Both are FullHD-capable displays (LCD native res: 1920x1080 so is Viera) so there shouldn't be any issue with resolution incompatibility. Viera HDTV is connected directly (no VCR receiver in the middle) via HDMI <-> HDMI.

The thing is that I managed to mirror the Windows 7 desktop with no problem. It shows up nicely, I can see task bar, all the icons etc. (i.e. What's happening on LCD gets duplicated on Viera.)

However, whenever I start a game in full screen mode the secondary display (Viera) goes black. When I start the game in windowed mode it shows on Viera just fine!

What the hell is happening here? Problem persists for all kinds of different games (Diablo 3 beta, Battlefield 3, Mass Effect 3, Gothic 2). I've also tried full screen video in VLC player with no problem whatsoever.

Regards, Jacob

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The games that you are having issues with most likely will only go full screen on the primary display, regardless if the displays are mirrored. Try setting your TV to be the primary display before launching the game. Worst case scenario is that you have to disconnect your monitor.

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OK, I'll give it a try. But the weird thing is that the mirroring in full screen worked correctly before. (I think before I installed second GPU in crossfire.) – Jacob Apr 30 '12 at 14:01
@Jacob: Oh, you didn't mention Crossfire before. I know SLI has some peculiarities with multiple monitors, I'm wondering if the same is true for Crossfire. – MBraedley Apr 30 '12 at 14:27
Yeah sorry, I figured if one of the GPUs in desktop mode isn't runing it wouldn't make a difference. I really don't wanna disconnect the LCD monitor in the end, because I wanted to watch my brothers gameplay. It's a lot cozier than looking over the shoulder. – Jacob Apr 30 '12 at 15:27
@Jacob: Sorry I couldn't be of much help then. The only other thing I can think of off the top of my head would be to disable Crossfire, which kind of defeats the purpose for a gaming session. – MBraedley Apr 30 '12 at 18:27
Ah, no problem. I just used UltraMon to set up mirroring. It sort of "did" work in full screen but not entirely. I could see mouse cursor ,and mouse cursor only, in the game menu but the movement was terribly lagging. The game menu itself couldn't be seen 'cause it was all black. The lagging occurred even out of the full screen game, on the desktop. Setting the Viera as primary didn't work either(in UltraMon as well as in Windows settings). Which I find just terribly odd! (When I mirror with Windows settings it doesn't lag at all, but the full screen games don't get mirrored.) – Jacob May 1 '12 at 19:42
up vote 0 down vote accepted

The problem resolved.
My secondary Radeon 5850 was somewhat glitching (it was secondhand). After removing it and running computer with only one 5850 the mirroring worked perfectly again even in 3D games. So now I am using only one GPU.

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