Greetings;
Purchased this set in 1990 (cost $4k) and calibrate it using The Perfect Vision's Laserdisc "A Video Standard".
It has provided impeccable service these many years however, on occasion lately, the screen will 'ghost out' as if someone wrapped the screen in muslin cloth.
Sometimes it lasts a few minutes, sometimes I must turn the set off for an hour and let it 'reset'.
Sometimes it happens when I first turn it on and sometimes it won't happen until I've almost finished watching a 2 hour movie.
I've taken the back off and vacuumed all dust out and it has open ventilation so I'm confident it is not overheating. All internal connections are secure and the tube shows no signs of discolouration.
Source material (dvd, vhs, LD, game console) does not matter, happens regardless (though not every day).
When this is NOT happening, colours and display look as good as the day I bought it.
Any ideas?
Thanks.

As an addendum, is there a dvd or BD equivalent to "A Video Standard" available for calibrating a PJ and screen set-up (which I will be purchasing shortly). Perhaps I should ask this elsewhere.
Thanks again.