You can desolder that jack and open it pretty easy if that's found to be the problem otherwise, this should be the right one:
http://www.ebay.com/itm/5PCS-5-Pin-1-8-3-5mm-Jack-Stereo-Headphones-Socket-nut-PCB-Panel-Mount-Chassis-/321642046094?hash=item4ae35c228e
To be sure simply ohm out the headphone jack in accordance with the diagram posted above...
http://www.ebay.com/itm/5PCS-5-Pin-1-8-3-5mm-Jack-Stereo-Headphones-Socket-nut-PCB-Panel-Mount-Chassis-/321642046094?hash=item4ae35c228e
To be sure simply ohm out the headphone jack in accordance with the diagram posted above...
