Headphone jack will not work

[bordonbert]

Hi, new ID Core 40 Head user here. Just bought the amp and like most of what I've found but I can't get a 3.5mm TRS plug to insert and work in the headphone jack. I have a number of headphone sets and all have the same problem, as do extension cables. And these all work in other equipment.

The plugs click through the various contacts on their way in but don't feel as though they are quite fully inserted. I get no sound at all through the headphones and the attached speaker still continues to work. The plug feels slightly wobbly too when it's inserted as though it is just not pushed fully home but the plug body flange is touching the socket as it should.

I have read online of one or two others having this problem. Can anyone shed any light?