It might be proper behavior or a bad sign, it really depends to which off the 8 pins you plug your 6 pin power - The ground wires are L shaped on the 8 pin connector and only 3 pins are +12V.
In that case, I can guide you through some diagnostics... No guarantee of course. Post some close pictures of the front and back of the card when it is fully naked and cleaned. Close up on memory, VRM, the Core so it is readable. It is pretty sensitive to static, try not to kill anything on the way
You will need:
- A 50MHz scope with an x10/x100 divider
- Well calibrated multimeter
- Laboratory power supply (0~14V, 0~25A, precisely limitable by both)
- Open bench bootable motherboard/CPU/PSU with onboard graphics and installed OS
- PCIe riser card is strongly recommended but you may get by without it with some Kamasutra practice
- SPI flasher (maybe)
- Rework station (with preheater if you have one)
- For memory or core, you will need an appropriate BGA matrix
- Nice to have: Thermal imaging device (FLIR, will make some tests so much easier)
We will make some measurements but I need to see the board first and draw the key test points.
In most cases, it funnels down to dead impulse generators, burned Mosfet pairs, shorted or blown capacitors, shot logical elements, shot cores or memory modules, interlayer short-circuits, etc... But you may be lucky and it is a burned fuse or bad bios.
P.S this card 99% not worth the effort in terms of time/parts vs final value with 1% a bad fuse or a bad vbios