Today was final attempt before sending C6H back, MB was on test bench and outside case.
In this video connected was:
ATX 24 pin
GPU with 2x PCI-e power
CPU (1700 or 3700X) and cpu+some case fans (flapping sound)
Here is first successful POST with Ryzen 1700:
And here is 3700X, the only thing what has changed is that system was turned off, CPU swapped to 3700X:
CPU AMD Ryzen 1700, MB Crosshair Hero VI, MEM FlareX for AMD f4-3200c14d-16gfx