Blue provide a tool for controlling the Yeti called Blue sherpa https://www.bluemic.com/en-us/products/sherpa/

This allows you to connect to the microphone and adjust the gain and volume settings. While I could connect and adjust the levels from the mic to headphones there was still no audio reaching the PC. So far apart from the Faulty HP Pot the ananlog audio chain appears to be working and the USB connection appears to be good.

There is some reports that the Blue Yeti does not work well with USB3 ports.  So I tried it on a MACbook pro osx and win 10 and win XP via Parallels VM. a Dell Tablet and a HP windows 10 machine - a mix of USB 2 and 3 ports with no change. I get Audio out but no audio in.

This is starting to look like the ADC of CM6400 may be faulty or some other internal fault in the chip. But dmage to the chip seems unusual as all the other functions so far appear to work.