Question Second GPU not recognised

[ransu]

I have 5 computers (~ 2-6 years old mobos) 4 of them have one GPU each installed, one PC has 2* RX 580.
The gpu´s installed are PC1 - nVidia 3070, PC 2 - Vega 64. PC 3 - AMD 5700 XT,and the 4th PC - AMD RX 6800 and the 5th with 2* RX580 working. I have 2 more GPU´s and would like to mine with them, adding them to a PC with one other card (one more VEGA 64, and one 5700XT.

I´ve - updated the BIOSes on (all) the motherboards
I´ve both tested with settings "4G Decoding" on and off (if the setting has been available)
I´ve tested PCI speed between AUTO and Gen1, Gen 2, Gen 3 (where available) on some motherboards.
I´ve changed msconfig in Win 10 from Selective startup to NORMAL STARTUP (load ALL devices) *while on some PC´s the settings jumps back to selective after restart (some say all services should be checked for it not to do so)
I´ve tested BOTH - VEGA and 5700 (as second GPU) where possible directly on the motherboard, tested with Phantec PCI-E ~20cm expansion cable, tested with 3 different mining raisers.
I´ve tested with separate PSU power to the 2nd GPU

As a single GPU, the "extra" cards VEGA and 5700XT works fine, but as soon as I add a second GPU (no matter which PC) I get into trouble. Sometimes "black screen, even no BIOS" after adding a 2nd card and starting. Most often computer starts, but DEVICE MANAGER cannot see any 2nd card (not even when SHOW HIDDEN is selected), and no 2nd driver can be installed.

I feel like I am doing something wrong (missing some detail to change or check) as none of the 5 PC´s accept the "extra" cards. Only one PC works with 2 FULLY SIMILAR RX 580 cards... taking out one and trying Vega or 5700 leads to same issue (2nd card not seen).

The PSUs are 2 PCs with 750W, 2 with 850, and one "old" with 650W.
All PCs have WIN 10 up to date
I´ve used DDU to clean away old drivers on most PCs, installed the working first GPUs with latest drivers.
I´ve "logically" tried to add the 5700 to the PC with one working 5700, and the Vega 64 with the other vega 64, but it doesn´t change the outcome, never finds the 2nd GPU.

Any suggestions are warmly welcome!

 

[Lutfij]

You might want to create a thread for each of your five PC's, why? Because you've muddled up all the parts and problems of your PC's into one thread.

In fact if you want to clean up your post, make sure you've listed the specs to each build like so:
System 1;
CPU:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
OS:

^ repeat for the next 4 system's.

 

[ransu]

You might want to create a thread for each of your five PC's, why? Because you've muddled up all the parts and problems of your PC's into one thread.

Yes, it wasn´t specific, and I could do that for one computer, my initial idea was that showing what I have tried to do on 5 computers, might show some step that I´ve left out (like one must check X in bios, or some setting in windows to get it to work).