Hi Mike and Bruce,
Did a factory reset and set fine for a couple of days, but today, off again. Checked panels on the pile but didn't have anything with a similar tuner so off to Ebay to haggle for a SSB with all the same numbers as seems the SSB has a variety of options, even using the same screen.
Many thanks - Chris.
With the new panel the set did the same, so thought replace all the caps in the P/I. Same again but when I switched channel to BBC1, also using colour bars on Scart, the problem disappeared so guess caused by a crap signal from channel 37 that doesn't bother other sets.