Windows 8 and 8.1 Forums


HD7950 won't work where 6950 does

  1. #1


    Posts : 2
    Windows 8 64bit

    HD7950 won't work where 6950 does


    So, I recently bought a Radeon HD7950, but when I put it into my PC, it caused all sorts of black screens and crashes etc.

    I used both a Radeon HD4950 and a HD6950 in exactly the same pc, and both worked without an issue. For my birthday I got a new 650W Power supply (replacing my old 500W, I thought this was the issue.) But when I put my card in, it worked for maybe 2 hours then the same things happened again, with the pc eventually becoming un-bootable until I put the 6950 back in.

    My PC setup is;
    Asus P8Z77-V LX Motherboard
    Fractal 650W PSU
    Intel I5 Processor
    Crucial M5 SSD
    Western Digital 80GB HDD
    Western Digital 250GB HDD

    Now, I know for certain that the 7950 is not faulty, as I tried it in my Dad's PC, (the one that previously had the 6950) and it worked fine. For some reason, the 7950 just does not agree with something in my system.

    Any ideas what would be causing this? Any help would be greatly appreciated.

      My System SpecsSystem Spec

  2. #2


    Posts : 2,191
    Windows 8.1


    So, I quickly reviewed the specs and here's what I found:

    The HD 6950 is PCI-e 2.0
    The HD 7950 is PCI-e 3.0

    The Intel Z77 chipset only supports PCI-e 2.0

    Many mobo manufacturer's are claiming PCI-e 3.0 support using a 2.0 chipset. How they can do that and how it would actually work is a mystery to me. Anyway, see if there is a BIOS option to run at GEN2 speed and see if that stabilizes your rig. Now, since we have not even maxed out GEN2 yet, I don't think you'll pay any performance penalty by doing so. Please understand that I am no expert in this area but I think it might be worth a try. Good luck.
      My System SpecsSystem Spec

  3. #3


    It's rare occasion for PCIe 3.0 could not run on 2.0, more likely your PSU can't cope with it. Just because it is marked 650wats does not mean it is or it does not have enough power on that branch.
      My System SpecsSystem Spec

  4. #4


    Posts : 2,191
    Windows 8.1


    Quote Originally Posted by CountMike View Post
    It's rare occasion for PCIe 3.0 could not run on 2.0, more likely your PSU can't cope with it. Just because it is marked 650wats does not mean it is or it does not have enough power on that branch.
    I agree that it will run fine on 2.0; however, the issue (as I see it) is that the OPs mobo has a PCI-e 3.0 slot and if it is set to run at Gen 3 (using the Z77 chipset), it might not work properly because of the stated Intel chipset limitation. BTW, I think his power supply is quite adequate so it will be interesting to see how the OP responds.
      My System SpecsSystem Spec

  5. #5


    Quote Originally Posted by my2cents View Post
    Quote Originally Posted by CountMike View Post
    It's rare occasion for PCIe 3.0 could not run on 2.0, more likely your PSU can't cope with it. Just because it is marked 650wats does not mean it is or it does not have enough power on that branch.
    I agree that it will run fine on 2.0; however, the issue (as I see it) is that the OPs mobo has a PCI-e 3.0 slot and if it is set to run at Gen 3 (using the Z77 chipset), it might not work properly because of the stated Intel chipset limitation. BTW, I think his power supply is quite adequate so it will be interesting to see how the OP responds.
    You really can't tell with PSU's just because of their rated wattage. For instance, my 600W PSU has 49a available on the single 12v rail but several 1000W PSUs I've looked at with multiple 12v rails can handle only a maximum of 40a on each rail, etc. It's not the overall wattage figure that is important, it's the amps-per-rail, and of course the general efficiency of the PSU that matter most.

    My 2GB 7850 is a 3.0 card but runs fine on my 2.0 motherboard--the limit of my motherboard. The fact his 79xx runs fine for a couple of hours indicates a problem other than that with PCI-e timings--if there was a problem with the PCI-e bus related to the timings then his 79xx simply wouldn't work at all from the start. Sounds to me very much like PSU problems would indicate, though.
      My System SpecsSystem Spec

  6. #6


    Posts : 2,191
    Windows 8.1


    My 2GB 7850 is a 3.0 card but runs fine on my 2.0 motherboard
    Hi waltc,

    The OPs situation is a bit different; in that he has an (advertised) 3.0 capable mobo with only a 2.0 capable chipset. I have seen many problems reported because of this isuue. Now, maybe the mobo manufacturers have found some way to work around this limitation but I'd sure like to know how they are doing it.

    Click image for larger version

    Its just not designed to run 3.0 so maybe the mobo manufacturers have tested it and feel otherwise?
      My System SpecsSystem Spec

  7. #7


    Quote Originally Posted by my2cents View Post
    My 2GB 7850 is a 3.0 card but runs fine on my 2.0 motherboard
    Hi waltc,

    The OPs situation is a bit different; in that he has an (advertised) 3.0 capable mobo with only a 2.0 capable chipset. I have seen many problems reported because of this isuue. Now, maybe the mobo manufacturers have found some way to work around this limitation but I'd sure like to know how they are doing it.

    Click image for larger version

    Its just not designed to run 3.0 so maybe the mobo manufacturers have tested it and feel otherwise?

    Heh... OK! That's one very weird mboard! It doesn't appear that even at 2.0 that it supports 16 lanes! (It should.) It looks like this is a bargain-basement mboard that isn't very happy with his premium retail gpu. I've only used AMD (since 1999) and I have to say this board is among the strangest configs I've ever seen! You might be completely correct. OP should definitely go for a mainstream mboard, no doubt about it.

    The fact that it runs for two hours before bombing out is also strange--and normally I would have said PSU. But in this case I can't say. Gotta' change that mboard--for sure--before doing more diagnostics.
      My System SpecsSystem Spec

  8. #8


    My house
    Posts : 148
    Windows 7 Home Premium x64


    my2cents, my friend built a new PC using a Z77 chipset and his GPU is PCI-E 3.0 and has never had this issue. Besides the PSU being the probable cause, have you updated the drivers to the latest 13.10 beta for Windows 8?
      My System SpecsSystem Spec

  9. #9


    Posts : 2,191
    Windows 8.1


    Quote Originally Posted by nenad285 View Post
    my2cents, my friend built a new PC using a Z77 chipset and his GPU is PCI-E 3.0 and has never had this issue. Besides the PSU being the probable cause, have you updated the drivers to the latest 13.10 beta for Windows 8?
    You answer is extremely generic! So, you think that because one configuration is known to work that all configurations should work as well? Any chance it is the same gpu and same mobo as the OP's configuration? I'll bet not. So, your answer is to just go out and buy a new PSU? My suggestion wil cost the OP nothing more than a bios change to test this issue. All the OP has to do is change the PCI-e 3.0 slot to run at Gen2 and see if that fixes his issue.
      My System SpecsSystem Spec

  10. #10


    Posts : 2,191
    Windows 8.1


    One more thing. Since the power supply keeps popping up as an issue, I decided to look up the power requirements for both the 6950 and the 7950 and the power requirements are the same for both cards:

    Video Card Comparison - GPUReview.com
      My System SpecsSystem Spec

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