I happen to have this same model, but have never opened it to see how the Jack is secured to the
"mother" board. Some Jacks are encased in small enclosures and firmly soldered to the PCB then butted against the casing of the keyboard. Others
are linked to the PCB by wires or cable and secured to the casing of the keyboard by a washer and nut. In this last case, tightening the nut should solve your problem. Still some others use a combination of the two methods.
It's conceivable in the first case mentioned above that the whole assembly (enclosure) has become unsoldered, or the contact terminals of the assembly have broken off. I would guess one of these possibilities would be the case here. If I'm right, the Unit will have to be opened up to effect a repair. I would counsel you to contact a reliable service professional to determine charges for repair. Also contact Yamaha for their charges. Good luck.
