Thanks Bruce,
Guess SSB as set OK when cold but after a few minutes OSG slows down giving the Green led, though suspect display bits are working OK, as vague illumination present.
Tried 'factory reset' from main menu, but will try your suggested option. Had a look on Ebay, and SSB is the only expensive panel - Often seems a guide to the issue - Chris.
Tried 'Self Check' and got 'Self Check' OSG top left, but nothing else 'till I turned set off and re-tuned.