MiniDP-VGA adapter woes

Having real trouble with a new Mini-displayport to VGA adapter (active) [] that I'm trying to use to connect a third monitor with.

Setup is as follows. I have a Radeon 6970 video card with two mdp's and one DVI port. I have three 24" samsung LED monitors that run at a native 1920x1200. I need this adapter to connect screen three to mdp 2 so I can use the remaining DVI port on screen three for other devices (Xbox, PS3, etc).

I have had this set up and working perfectly where I've run the three screens on the DVI ports with DVI and mdp-DVI-D cables/adapters. It seems the mdp-to-VGA adapter should work here, given the relatively low resolution of 1920x1200, that the adapter claims to support it and I read of others using it for this purpose.

My problem is screen two, when connected in this fashion, reports as a 'Generic non-pnp monitor'. This limits the monitor to 1600x1200.

I have tried to manually install its driver - this didn't help. I've tried unplugging the power cable for 5 minutes (as some recommend), to no avail. I've tried unplugging and replugging the mdp-VGA cable with the monitor off and on, again to no avail.

I'm out of options and about to give up. Any advice would be much appreciated.
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  1. I should maybe add, in case it's relevant that I managed to manually install the monitor driver file however now when I go to Display properties/screen resolution instead of 'generic non-pnp monitor' its called 'Display device on: Mobile PC Display'.

    I have no idea why. Still limited to 1600x1200.

    Under Devices and Printers I now see (correctly) two SyncMaster SA450)S24A450BW-1 monitors, one with (digital) and one with (analog).

    Still pulling my hair out. :)
  2. Well, latest update is I tried moving cables around the DVI slots to no avail.

    Then my new MSI Radeon 7970's arrived prematurely today and I just put them in. Different port set-up now and I still can't get it working. This card has 4x mini display-ports and 2 DVI ports, one marked as supporting VGA but I can't get it to run over 1600x1200 on the 3rd screen.

    I've given up unless someone has some other idea on how I can hook up the PS3 and PC's DVI cable to the one DVI socket on monitor 3. Maybe run the DVI cable from the PC to screen 3 and the HDMI from the PS3 into a HDMI/DVI switch that would have HDMI and DVI inputs as well as one HDMI output and then I could toggle them that way. I can't find a switch with HDMI AND DVI, however.

    Bah - another vote for port unity.
  3. Solved this with an HDMI switch. HDMI running from PS3 and Xbox to the switch, then from the PC via an DVI-D-to-HDMI cable. HDMI to DVI-D cable connects from the switch to the PC. Toggle inputs on the main central monitor to switch devices. It's not ideal and occasionally required a reboot on toggling back from PS3 to PC until the latest Radeon drivers. Since then, all working fine.
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