There is a know issue with this radios about this: usually the kenwood interface for this radios take power from the radio not from the PC, and the power is taken from the same rail the LCD leds are powered.

For some reason with time (or a mic cable short) a medium power resistor burn out in the main board and get the front panel without +12V, that not a problem to the normal operation as it works on +5v, but the backlight gone off and the programmer has no power to feed from and always fails to operate.

Can you check that please?