HD7790 Crossfire strange core clock behavior


First of all, i know that crossfire isn't the easiest thing to deal with, but I received the second card from my sister so i try to get it work :P

I've got two ASUS HD7790 1GB running on crossfire 8x/8x, on motherboard A970-G46. Both overclocked to 1200mhz on core. When I look on Afterburner Hardware Monitor, it shows that the clock constantly changes. When I play, it never reaches 1200mhz, or even 1000mhz. Performance is also terrible, very often it's better to play without second card. Efect fades only when I remove second card, switching off crossfire doesn't help. Any idea what do i have to do? I installed 13.12 WHQL drivers, but it didn't help.

PSU: SilentiumPC Deus 600W | CPU: AMD Phenom II 965 @ 4.0GhZ
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More about hd7790 crossfire strange core clock behavior
  1. first of....get a better psu. it is very likely that the psu is not giving enough power to the gpu s.

    secondly, revert the oc to default clock and see if that helps.
  2. My friend has two hd7850 with the same PSU and it's running well. So I thought it should suffice. Reverting didn't help.
  3. did you update your mobo bios. if not you can download the latest from msi website, see if that works.

    by the way what games were you playing??
  4. Yeah, i did update bios yesterday. Played The Witcher 2, BF3 and CS:GO.
  5. the psu should not be the problem. it is not a super cheap psu. Both of the cards have to be at the same speed to run well. you problem might be; 1 card can't hold up> downclocks> pulls down the other card
  6. Both should work on 1075mhz or 1200mhz, i tried both options. What do I have to do?
  7. are the gpu's at stock voltage?
  8. Yes, they are. I also tried a bit higher voltages, but it didn't help.
  9. I think your gpu's supports PCI-Express 3.0 but your mobo supports only 2.0?
    It does matter with the performance of your gpu.
  10. Yes, it doesn't support 3.0. But when there was only one card, everything was good. Is that really the reason of downclocking?
  11. Flymanos said:
    Yes, it doesn't support 3.0. But when there was only one card, everything was good. Is that really the reason of downclocking?

    I'd say that was an unlikely reason, PCIe 2.0 has been around for a while so the majority of boards are going to be PCIe 2.0 and it makes little sense to have a card that is not backwards compatible and requires a new motherboard.
  12. I don't know if this is an important information, but there's also something strange with GPU usage:
    Captured when playing.
  13. Best answer
    I tried using one for folding and saw that it couldn't maintain a flat line when under a constant load so I think it's either the architecture or drivers myself.
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