Setup: Samsung S27A950D attached to an Alienware M18x running dual nVidia GTX 580M with the display extended across laptop screen and the 950D. Because the M18x has a mini-DP port I use a short (6 inches) miniDP-DP adapter cable.
The 1.8m cable I ordered separately at the time the 950D arrived (no cable included with the screen) works fine, both screens work as expected (well... getting 3D seems to be a problem but that's probably another issue).
Then I ordered a 3m cable from Amazon, or one of their re-sellers to be precise and when I connected the 950D using that instead, the screen didn't activate, only the laptop monitor. I tried various ways of re-setting the display to laptop only then extending it, tried the cable the other way round etc - nothing.
So I arranged to send that cable back for a refund thinking it was faulty and bough another 3m cable online - same problem
So it seems that this setup has hit some kind of limitation - has anyone else had similar problems or is anyone aware of limitations in the length of cable that can be used?
Is it a possibility that the cable quality isn't very good and a more expensive one might work better?
I remember reading somewhere a while ago that HDMI video quality drops off as cables get longer, but the issue then seemed to be reduced picture quality rather than nothing at all?
Be grateful for any input.
The 1.8m cable I ordered separately at the time the 950D arrived (no cable included with the screen) works fine, both screens work as expected (well... getting 3D seems to be a problem but that's probably another issue).
Then I ordered a 3m cable from Amazon, or one of their re-sellers to be precise and when I connected the 950D using that instead, the screen didn't activate, only the laptop monitor. I tried various ways of re-setting the display to laptop only then extending it, tried the cable the other way round etc - nothing.
So I arranged to send that cable back for a refund thinking it was faulty and bough another 3m cable online - same problem

So it seems that this setup has hit some kind of limitation - has anyone else had similar problems or is anyone aware of limitations in the length of cable that can be used?
Is it a possibility that the cable quality isn't very good and a more expensive one might work better?
I remember reading somewhere a while ago that HDMI video quality drops off as cables get longer, but the issue then seemed to be reduced picture quality rather than nothing at all?
Be grateful for any input.