Graphics card only works in x4 PCIe slot

thiagofc · October 16, 2021

I apologize in advance for the long post. First of all here are the specs of my build:

MB: Gigabyte B450 Aorus Elite;
CPU: AMD Ryzen 5 3600;
GPU: MSI GeForce RTX 2060 Super Ventus GP OC, 8GB;
RAM: G.Skill Ripjaws V DDR4 3200mhz CL16 (2x8GB);
SSD: Intel 660P, 1TB, M.2 NVME;
PSU: Corsair 550W 80 Plus Bronze CX550.

This setup worked fined for many months with the graphics card installed in the x16 top PCIe slot, until a few months back, when I was installing a new CPU cooler and had to remove the GPU to make it easier to fit. When I installed the GPU back in the x16 slot, I forgot to plug in the GPU PSU cable before powering on the system. I quickly realised this, shut everything down, connected the cable and tried again, but was unnable to get a post. The VGA LED on the MB was also on when powering on, indicating a problem with the graphics card.

After some panicked googling I tried reseting the CMOS, reinstalling the RAM and a bunch of other things that did nothing. After a while I placed the GPU in the bottom x4 slot and the system powered on and posted normally. Installing it again on the x16 slot still did not work. This, along with some forum posts saying that turning the system on without the PSU cable connected to the GPU could mess up the internal circuits of the board, made me think the problem was with the MB. To confirm the GPU was fine, I tested it with a friend's system and it worked fine in the x16 slot. I then sent the MB to Gigabyte to fix the problem, but according to them the board was working fine. They ran some standard tests and sent it back to me. I then sent it to them again claiming the issue was still present and they said once again that the board was fine, and even sent me a video of a graphics card installed in the x16 slot and the system powering on and posting.

I have also tried updating the BIOS (including the GPU's) and even reinstalling Windows, with no success. The only thing I haven't tried is installing a different graphics card in the x16 slot myself, since I don't have access to one, but the video from Gigabyte proves it works with a different GPU. I have been using the pc with the GPU in the x4 slot, but the performance in some games is not the same... I don't know what else I can try to do to figure out what is wrong.