My 52" rear projectionT.V. Is about ten years old and for the past year the picture takes a while to appear. Sometimes the picture will blink on and off for hours, while other times the picture will only blink for a minute or so and then stay on. When the picture isn't on the t.v. Functions normally.

You generally have a weak capacitor in the power supply, that will delay a startup! Second to these are poor grounds on any and all ICs attached to heat sinks. A heat sink is a large metal piece mounted on the TV board. It is a cooling fin to reduce heat on the IC. The pins are underneath these, and will have cracked rings around them. These of course reduce voltage and a promote a slow startup. Please check all capacitors with a capacitor checker and look closely underneath the TV board for bad solder grounds and resolder!