Hello
It may be due to the fault of its picutre tube base socket. Some of them may show this type of fault eventhough it is a new one. Picture tube base socket is located at the picture tube bas card itself. It is directly soldered to the base card, throu which the connections are going into the picture tube via its pins. You just open the tv, and pull it out [not make any shakes while pulling it, as that may bed the picture tube pins, or iven break the picture tube neck. Just pull it straight out, and refit it at the same way as you pulled it out, for two or three times. Sometimes this will retify the fault, as this process will remove any loose contact between bascard socket and picture tube pins.
If this doesn't hlep, desolder it out from the picture tube base card, go for a similar type and pin confuguation. Replacing it will solve the problem. As you replacing the base socket, look into the base card for any loose soderings are there too. OK.