I recently purchased two Dell U2417H monitors to upgrade from my existing Dell S2440L and have an issue running them both from my HD5850 card.
I have the main display hooked up through the display port output on the card to the mini display port input on the monitor. This display looks and works great.
The secondary display i have hooked up through the hdmi output on the card to the hdmi input on the monitor. This display is a bit brighter and the colors a bit more washed out (which i can probably fix via the monitor settings) but the display will flicker every so often. Often enough to notice and be quite annoying. It seems to worse when the main display is changing (i.e. desktop picture cycles, or playing a movie, or loading a webpage, etc...) but even if nothing is changing it will continue to flicker.
I tried using a mini display port to hdmi cable, with the mini display port end in the monitor and the hdmi end in the 5850 but the monitor won't even recognize that there is an input attached in that setup. The same happens when I use a DVI to full size display port cable with the full size display port on the monitor and the DVI in the card.
I have also switched the cables and verified that the flickering follows the hdmi cable, and does not appear to be a faulty monitor unless they are both exhibiting the same fault (unlikely).
I believe I have the latest drivers, as they stopped updating them for my card. I also installed the Dell specific monitor drivers from the included cd.
I've ordered two DVI to hdmi cables in order to attempt to use the same outputs (both DVI) on the card and the same inputs (both hdmi) on the monitors to see if that will possibly correct the issue. After that I'm at a bit of a loss... might just upgrade to a newer card. Before shelling out the cash for a new card I want to make sure that a new card would fix the problem.
Any input would be much appreciated.
Computer Specs: Intel Core i7-870, Asus P7P55D-E Pro, HIS Radeon HD 5850 1GB, 16GB G.Skill Ripjaws, 650W Corsair PSU