Sapphire 7850 GPU wont detect in PCIE x16 on z77 UD3H, works fine in x8

[CBlah]

I have a Sapphire 7850 non OC gpu that seems to work fine on my Z77 UD3H in the second PCIE x8 slot, but will not detect in the PCIE 3.0 x16 top slot. I am trying to determine if it's a motherboard, gpu, or psu problem--or something else entirely. The fans on the gpu run, but no output to the monitor or recognition in the bios. The mobo bios is updated to the latest non-beta version, I have tried resetting CMOS through a variety of methods (removing the battery, hitting the switch, etc.).

I have a silencer mk2 750w power supply that (I think) should be good enough to run two 7850s, much less one.

I took the gpu card to Frys last weekend for them to test on a system there, and they told me it worked fine at 3.0 x16 on their system.

The parts are otherwise new, so there is no dust or anything in the pcie x16 port. The contacts on the gpu look fine, as far as cleaning them.

A similar issue occured with an ASRock z77 Extreme 4 board I had and returned (after my Fry's trip led me to believe it was a motherboard problem). Again, the card only worked in the x16 slot set to Gen 1 and worked fine in the x8 slot. It seems unlikely to get two motherboards with the same issue in a row, so I'm thinking it is probably not the motherboard...but who knows?

Barring some new ideas, my next step is to buy a new gpu card and psu from a retailer that I can return the parts to, and test the parts individually in my system to confirm that either another gpu may work in the x16 slot or that another psu may get the card working whereas my silencer mk2 can't get it working in the pcie x16 slot.

Has anyone encountered or solved a similar issue? Or has any other ideas to try?

Thanks!

[wazza300]

Re: Sapphire 7850 GPU wont detect in PCIE x16 on z77 UD3H, works fine in x8

disabled onboard graphics first? then switch to the 16x slot

[Acebmxer]

Re: Sapphire 7850 GPU wont detect in PCIE x16 on z77 UD3H, works fine in x8

Also try setting first dispaly to "PEG" and then try setting first PEG priority to PEG11 I believe. The second thing could be worded differently not something that needs to be changed but try and see.

[-AB-]

Re: Sapphire 7850 GPU wont detect in PCIE x16 on z77 UD3H, works fine in x8

I am having the same problem on an ASRock Z77 Professional motherboard. I posted about it in this thread which I believe you have already come across.

I am not sure if you noticed, but I did manage to get my card to work in PCIE 3 x16 mode. Initially all I had to do was power on my PC, let it boot into Windows, then wait one or two minutes, power off and then power on again. I had to repeat the steps each day I powered on my PC. But few days later that was no longer working. So then I found out that if I would set my PCIE link speed to Gen 1 and then boot into Windows and let the PC run for about five to ten minutes and reboot and set the link speed to Auto, it would again work in PCIE 3 x16 mode. But as days went by, the five to ten minutes became twenty to thirty minutes and soon it became hours. Last time that it worked, I had to use my PC for about four or five hours. I had tried setting the link speed to Auto earlier, but it didn't work. Anyway, that day after it started working, it didn't work for long. It had been running with link speed set to Auto for about 30 minutes or so. I was away from the PC for a while and when I came back, I noticed there was no display and Windows was not responding. I pressed the reset button and there was still no display. So I had to set the PCIE link speed to Gen 1 again.

The next day I took my graphics card to the store, they told me their service center was closed and asked me to go directly to distributor. So I did, but it was late when I arrived at the distributor's office and they said that I can submit the card but they can only test it the next business day. So currently my card is with them.

Anyway, even I was planning on buying another motherboard in case the graphics card turned out to be fine. I was planning on buying a cheap one like the Gigabyte GA-H61M-S2P, which seems to support PCIE 3. But thanks to your post I won't have to. :D

I have a 700 watt power supply that I can try once I get back my card. And maybe I can buy a cheap Geforce 600 series card to try. Like the Geforce GT 610.

I hope it's not the processor that's faulty.

[hansip87]

Re: Sapphire 7850 GPU wont detect in PCIE x16 on z77 UD3H, works fine in x8

I've had this problem too, it's not processor fault, it's the PCIe switches problem. I've had my motherboard serviced and they said it's the problem of the PCIe switch (the ones they use for splitting lanes with the second slot) a single PCIe slot mobo won't have this kind of problem.

So either you have to do with decreased speed, or you have to RMA/fix the board like i did.

[-AB-]

Re: Sapphire 7850 GPU wont detect in PCIE x16 on z77 UD3H, works fine in x8

I've had this problem too, it's not processor fault, it's the PCIe switches problem. I've had my motherboard serviced and they said it's the problem of the PCIe switch (the ones they use for splitting lanes with the second slot) a single PCIe slot mobo won't have this kind of problem.

So either you have to do with decreased speed, or you have to RMA/fix the board like i did.

Thanks a lot for the info. You just saved me a lot of trouble. :)

I guess I will just get my motherboard serviced.

Must be a coincidence that the OP got a Gigabyte motherboard with the same problem.

Anyway, thanks again.