Hi
The K3 is turned off by CAT command not by the hardware signal, but if the hardware signal is kept active when the shut off command is received, the K3 will be in a middle mode, display backlight on but not showing anything. There is not much between the CPU and the output, T1 a FET-transistor = FDV301N which is showed on page 233 in the manual. They are very rugged we have not changed many during the years
73 de mike