Erratic connection, not bad solder problem to pcb, internal failure
probably loss of plating contact surface.
Seems pointless trying to replace original dual concentric "socket",
bound to be proprietary and so will also fail after warranty + 1 year.
Some sort of polarised mateable line plug and socket with a well
anchored stub of lead , soldered to the pcb inside, instead. The
diverter switch in the socket just switches an LED on and off and has
been defunct for ages anyway.
So just 2 wire line connectors male and female for 20V ,3A. But what
type of non bulky, hopefully side by side axial connections, ie not like
3.5mm (3A anway) or dual concentric (no line sockets easily available).
At the moment I'm thinking of moulding up my own connectors , as I
cannot think of anything off the shelf. Using a pair of Q or Trident
type sockets and pins, offset axially , to give the polarisation.
Cosmetic appearance does not matter.