One final thing you could probably do while waiting for the final repair to be done.
Currently, whenever you play the key with faulty AT sensor, it plays as if with maximum AT. Right?
So, you could unsolder the white wire at T3 and solder it to the T3 of the next key to get the right default voltage (-0.4V).
An other solution would be to use two 100k resistors soldered in series and forming a bridge between -15 and +15 and then solder the white wire between the two resistors (to recreate a voltage divider).
