Problems with a Cambridge Audio DAB 300 Digital Radio Tuner, any geniuses out there?

My baby is just over three years old and I have had her running most days of her life I think possably the start up memory has become corrupted . The problem is now whem I fire her up I get "Station Unavaliable" so if i flick between the pre-set stations eventualy she will find the station at signal strenth 60-90 ish (very bad) and after 10 minutes or so it will come down to signal strenth 0-2 ish (good). I thought if I disconnect the DAB from the mains eventualy the station memorys will be erased and I can start anew. My question is how long should I leave it without power to make absolutly sure all old settings have gone and I have a virgin DAB again?