DisplayPort with HD5770/6870 and BENQ LCD not working


I've got a very annoying problem. I had a Sapphire HD 5770 and wanted it to connect with my BENQ BL2400 with DisplayPort (no adapters/converters what so ever involved, just DP->DP). Before I connected to display with DVI but then I wanted to setup two additional displays which both only support DVI and because the BENQ doesn't support HDMI the only other way to have three displays connect to the graphics card was using the DisplayPort. I therefore bought a DP cable which works nicely on my Dell laptopbut didn't display anything with the Sapphire HD 5770. Because both cable and BENQ worked fine with my laptop, I assumed that the DP-Out on the HD5770 was broken and exchanged the card with a Sapphire HD 6870 hoping that everything would work fine. Back home, the new card is now having exactly the same problem: BlackScreen/"No DP-Signal" on the display or sometimes it works but has a lot of graphic errors (flicker, bars...).

The problems start as soon as the ATI-Drivers load (both Windows 7 64bit and ArchLinux with newest Catalyst). Before the drivers start up, the output is just fine, no errors.

I would really really appreciate any help, I don't want to return the second card too, telling the reseller again that DP is broken on that card.

Thanks a lot in advance!
4 answers Last reply
More about displayport hd5770 6870 benq working
  1. Since your output is fine before driver load
    I dont think it is hardware related

    under display manager are 3 displays enabled?
    also how are you setting your resolutions?
    does CCC detect the DP display in display manager?
    In windows did you check under screen resolutions
    by right clicking on desktop?

    I know these are some simple questions
    and I dont mean to insult you
    but I always check the basics first while
  2. Thanks for your reply. I'm right now only connecting the DP display and are getting the errors, so it's not at all about the triple head setup. CCC detects the display just fine and sets the correct resolution to 1080p. If I manually set the resolution at the max 800x600 or below, then everything works just fine....
  3. maybe a new driver for your DP monitor?
    Check BenQ site for latest driver
  4. Seems to me that BenQ doesn't offer any drivers for my display (although there are some shipped with a CD, but not on their website).
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