Remove the Main digital board and check the resistance to ground at the Vias points which are the path for the audio signals.
Is the measured resistance below 19 Kohm?
Yes
Repair/Replace the Digital Main board.
No
Repair/Replace the Terminal board.
The next pictures show the location of the Vias in the Main-Digital Board. These Vias are the paths for the audio signals. Check the waveforms and/or the resistance at these Vias. Digital Main Board,
