I can't connect via serial console either. I have a USB/TTL cable (tested the cable to make sure it works by shorting white to green, text appears on my screen as expected), using picocom in a OS X terminal window. Picocom opens and I can connect to the serial device, but nothing happens after terminal ready, even when I plug the cable in before boot, I don't see boot logs, and I can't type anything into the window. I've tried both armbian distros, multiple installations of them, nmap shows port 22 closed and ssh connection is refused.