[Arran]

Terry;
  So there is no indication as to what that hole may have been for? It looks like whomever added it did so in a fairly professional way as it's a clean hole. About the only way to make that invisible would be to patch over it with a piece of veneer, preferably a strip from top to bottom, either that or make use of it by adding an input jack or a headphone jack. I was sort of wondering if maybe the power switch on the chassis was bad, I've seen bat switches added to radios for that reason before, or to add some sort of input or output jack, but you say that there are no extra wires or remains of under the chassis?
Regards
Arran