You may also have to throw the switch on the KIO3B Main board if you only have the USB cable. Very old boards did not have this switch, in that case you will need the RS232 interface to the RJ-45 jack and set RS232 to 38400. See https://ftp.elecraft.com/K3S/Manuals%20Downloads/E740280%20KIO3B%20Installation%20Rev%20A3.pdf Keith WE6R