I had been running an Asus Prime RX 9070 XT alongside an Asus ProArt RTX 4070 Super, but I wanted a second RX 9070 XT for better Linux support and more VRAM. I tested an ASRock Steel Legend RX 9070 XT first, and either Asus card worked with it individually. However, when I installed both Asus Prime cards together, only one appeared during POST, in lspci, and in Windows tools such as Device Manager and GPU-Z. Each card worked by itself in either PCIe slot, and both Prime cards had the same VBIOS version, so I suspected power delivery, the PCIe slots, or the PSU. The system uses a Ryzen 7 7800X3D, an Asus ProArt X870E-Creator WiFi motherboard, a Corsair RM1000x (2024), 64GB of DDR5-6000, and two M.2 drives that don't share lanes with the graphics slots. Each Prime card uses three 8-pin connectors, and one splitter cable was involved because of the available PSU ports. The issue turned out not to be the PSU or splitter: the motherboard's plastic shroud around the right-edge connectors interfered with properly seating the bulky graphics cards. Once I opened the case and reinstalled them carefully on a table, both cards were detected.
2 Answers
Since each card works by itself in either slot, try testing each one in the secondary x16 slot and then test both cards together. That helps separate a faulty GPU or slot from a power or installation problem. Also, make sure every power connector is fully seated and avoid assuming that a card is properly installed just because the retention latch clicked.
The splitter could still be worth testing, since a system can fail to initialize a GPU even when the cards aren’t reaching their maximum rated power. Try one card with the splitter and another standard PCIe cable, then compare that with a setup using dedicated cables. If detection changes, the cable arrangement is suspect.
I tested the cards separately with the same cable arrangement and confirmed the splitter wasn’t the cause. The real problem was user error during installation: the motherboard shroud was obstructing the connectors, so the cards weren’t fully seated.
That suggestion pushed me to take another careful look after I’d slept. I opened the case on a table and found that the motherboard’s plastic shroud was getting in the way of the cards seating correctly. The bulky coolers made it especially easy to install them slightly wrong. After reinstalling everything carefully, both cards appeared.