Fast Track Duo headphones dead on left channel only

[Gandy]

Hi all, I'm prepping a session for a job tomorrow and I've found that the left side of my headphone output is dead on my Avid fast track duo. I get audio from both left and right main outs as normal but can't get anything on the left HP out. Adapters checked, headphones checked, headphone knob isn't scratchy or anything it's just dead. Nothing visibly in the socket and contacts are in the correct place. Any help here, could this be a digital thing or is the hardware dead? It's only a couple of years old and was working fine last week!!