+ AA6YQ comments below
Resolved. RS232 Config item was set at 38400. Wrong. Rolled RS232 to USB and all is well. At age 86, items like this do not recall correctly.
+ That's why directing the DXLab Launcher to populate a Workspace when everything is working correctly is so important. Known good settings can then be restored with a couple of mouse clicks.
A kind, smart Elecraft tech helped me test and find this. On another happy note, he told me not to worry about parts inventory as Elecraft can repair most boards unless a catastrophic event occurs, CASE CLOSED.
+ If the K3S "RS232 Config" menu offers 38400 as a choice, why is it wrong? The K3S manual notes that firmware upgrades are automatically conducted via the serial port at 38400.
+ Did you have Commander configured for a baud rate other than 38400?