Many thanks for your response. I had no luck after disconnecting the equipment from the power source for 5 minutes, but made progress with your second suggestion. There is still some work to do because although the AM and FM radio now work (speakers and headphones), the DAB band seems to have disappeared altogether. I intend to try another major re-tune today. Meanwhile, do you have any interim thoughts on that, please? By the way, you'll certainly get your max star rating.
I have indeed clicked your 5 star rating; hope it has gone through OK. I think the problem I had might be cracked now. I have just found out that the 30+ channels downloaded that I thought were "old" FM are probably DAB. A typical radio frequency for these is 225 MHz; is this sufficient to identify it as DAB? The problem is that my equipment manual says there should be a separate band to tune in called DAB, but this term has not appeared at all on the tuner monitor screen. By the way, I am now receiving these channels via the speakers. If you confirm that what I have is DAB, we may have the problem solved. Can I still continue to consult you if I still have related issues in the near future?