JVC av-27f802 i'art power off problem?

I have a JVC I'art av-27f802 flat screen television which has a problem when you switch it off.The sound and power indicator will go off,but the picture tube will remain powered on,having to unplug the television.Once plugged back in,the tube will remain off until you turn the set on again.Had set repaired under warranty for same defect.Problem was repaired,but started to happen again after warranty had expired.Thanks for your help! JP