Primary x16 PCIe slot sometimes gets stuck in x4 mode

[Melcar]

I have this weird problem with my Gaming K7 (AM4). Well, it could be the GPU for all I know.

I few days ago I noticed my video card (RX 480) was running in x4 mode. Both Linux and W10 reported this, even when a game was launched. So I removed the card and cleaned connectors. Now my PCIe speed was reported as x16 correctly.

Yesterday I reinstalled my old Xonar DX card (in the last PCIe slot at the bottom) because my onboard started to piss me off (electrical noise). A few hours latter I remembered why I stopped using that card and removed it from my system. When I booted back up I found my video card running at x4 again, both Linux and Windows. Opened the case again to re-seat the card (did not clean the connectors) and this time the card was stuck in x8. So I removed the card again and this time cleaned the connectors. Now the card is at x16 again.

So what do you guys figure it is? Unfortunately it did not occur to me to check if installing the Xonar card caused the primary PCIe slot to downgrade to x4/x8 mode (no idea it could go as low as x4)? If that was the case wouldn’t it revert back to x16 once I removed the Xonar? You think it’s just the video card? It reverts back to x16 mode after I clean the connectors and re-seat it.

[Hako]

You may want to check this thread out maybe something in there will help you:

Zenith Extreme & 1950X ... 3rd slot stuck at 8 lanes

This has been quite frustrating. For a while now (and possibly since the very beginning) I have known this system to be very stable, with one quirk. The 3rd slot (which is a x16 slot) only connects to the GPUs I put in it at 8x. The problem here is the standard GPU slot (slot 1) is completely obstructed by the NH-U14S TR4-SP3 cooler. Yes I have adjusted its mount with the 6mm offset it provides, and this still is short by probably 4mm for a typical backplate-having GPU to fit in that slot. I’d need to rig some janky kind of riser dealio to make it fit, which it really won’t given the case I have this in now (or would intend to put it in). I’m not sure what I’m going to do once I reseat the CPU and this issue persists. Yes I have updated the mobo’s bios. Yes I have reset CMOS and lost all my clock speed tweaks. I will probably have to just accept it for what it is. I just really don’t like this because i’ve invested a good amount into the machine. It’s got 96GB of RAM. I thought I was being clever getting ECC Samsung B-die memory for it. now I realize i got slapped with 1/2 the expected PCIe bandwidth on the system optimized for I/O. What could cause it? I have carefully inspected the slot on the motherboard. Multiple GPUs all run at 16x in other machines and at 8x in this slot on this machine. What would be nice is if I can use a pcie riser to confirm that the first slot runs at 16x… [image]