I hook up the USB cable for my KX3 to my Macbook only once in a while. Like many things electronica, it works flawlessly if you use it every day, but if you put it away for a month or two you/it forget how it works. Here’s some troubleshooting. This is not for connect-it-the-first-time. For that, see http://www.worldwidedx.com/elecraft-kx3/140013-elecraft-kx3-firmware-update-mac-os-x.html .

• In the KX3 Utility, on the Port tab, be sure the leftmost control says “usbserial-A901…”.
  • If it says “Bluetooth”, you aren’t going to talk to your KX3.