My DC503 also has nothing connected at the lower of the two points in your
picture. On my board there are four of these holes in a row with no wires or
components attached, partky hidden by the shaft of the function switch. They
are 'vias' used to transfer a PCB trace to the opposite side of the board for
routing purposes. There is another row of 7 similar vias towards the
connector end of the same board.

Roger