Zeus, I had a look at the socket in the 308 and you can only test with a multi-meter if you take out the board as the centre pin is terminated to the pcb under the socket. the two pins in front which I beleive you are testing are the ground and the other one is dead on the board.use a mono plug. check if you have sound on jack with butt phone or line in on pc.

“I have not failed. I've just found 10,000 ways that won't work.”