The system works for FM- that must mean the basic system is OK.
It 'sees' DAB stations so so reception must be OK.
It is not converting.
Assuming that you have sussed how to work the thing[pressing all the right buttons] it could mean a component failure.
There is not likely to be a repair option.
The usual 'No user serviceable parts inside' rule would apply and also to a 'repair shop' to because the unit is all on one board and replacements would not be available.
But you local Sony dealer may advise something different