Fixed !.....so I was dubious about replacing the ic as I know when removing the nand on the iPad 4 you really are playing with fire, as the touch ics are on the back of the board, and get it slightly too hot and you end up reballing all three touch ic's which are a total nightmare because of all the underfill.
So I decided to proceed with caution and grind the audio ic off the board instead, slowly working my way down to the pads.
[image|1220909]
I then heatsinked the !&&* out of the three touch ic's on the back of the board with a offcut of alluminium, taped to the board with kapton tape and some flux on the ic's to aid thermal transfer between the ic's and the heatsink.
I then fluxed the pads and placed the new chip.
[image|1220910]
I then checked for solder balls under the microscope on the touch ic's and breathed a sigh of relief !.
I then tested it and I'm pleased to say it's no longer in headphone mode and audio works fully as expected, so looks like an internal problem to the ic itself as when reading the headphone detect line in diode mode before it read OL, so looks like something inside was broken, either that or possibly broken solder balls, but because it was an underfilled chip no chance was it getting re flowed.
[image|1220914]