I suspect the shadow mask within the the CRT has become magnetised and the auto degaussing has stopped working.
Most likely cause is that the temperature dependant resistor has gone open circuit that feeds the degaussing coils.
Fujitsu Lifebook P727 laptop review
Best of the Grad Shows 2017: University of the West of England (UWE)
Best value Mac: Which is the best £1249 Mac to buy
Les meilleures GoPro 2017