Looking at the connection panel,you should see a round Din socket with light brown plastic plug in it,but with no wires!!! If you can see the socket but not the plug,then thats what's causing your problem . That socket is a port for an auxillary in/out device,eg.a mixer or equaliser,but people often think it's another input and take the plug out,to connect something like a Bluetooth receiver,which would work,but also interrupt the signals for the other sources. If your plug is missing,you can source one from Danish Sound Parts, that sponsors this site. Nick