Hi Gary,
Like I wrote yesterday, none of the other things you wrote would have any effect on the output
audio. The jumpers only affect the microphone audio, power has nothing to do with it, assuming
the control panel is otherwise working.
If that particular cable is okay, then I would contact Microbit about a possible repair requirement.
Try another audio cable between the TS-480 and RRC in the meantime if you haven't.
73,
Mitch DJ0QN / K7DX