"Smarty"
"Phil Allison"
"Smarty"

** The set is a 19 inch Sony - so it is a Trinitron type.

I suspect the behaviour is typical of Triniton with a magnetised
aperture
grille. The degaussing thermistor may have failed in the set and at the
instant of failure left with a parting blow by magnetising the grille.

The OP can check for this by noting if the usual switch on " bong" noise
still happens.

He can also bring a magnet near ( not touching) the screen and see if
that
tends to fix various areas.


This is altogether surprising to me, but then again I virtually never did
TV repair.

** I did - in the B&W days in Australia, circa 1972 and onto to 1976.

But it never grabbed me.



I have a bit of trouble understanding why a magnetized shadow mask or
aperture grill would still allow a black and white image to be correctly
displayed. If beam alignment were 'spoiled' by residual magnetic
contamination of the CRT near the faceplate or if the purity rings were
not doing their job, then the outcome should be color blotches regardless
of whether chroma saturation is absent or present. I hope this specific
problem is eventually solved so I can hear the actual cause of the
problem. This old dog loves to learn new tricks !


** Once, I was optimistic enough to buy an "re-conditioned" ( = re-gunned )
26 inch colour tube for my own TV. It was a regular, three stripe, full
convergence, colour Toshiba CRT with removable yoke dating from the early
1970s.

The tube supplier wanted the old tube back so I had to have it out of the
set and ready - the exchange took place around 11AM. I fitted the tube
that afternoon and after a heck of a lot of work was able to watch my
favourite TV programs the same evening.

Doing a full convergence "ab initio" on an aging and rather heavy TV set is
not for the faint hearted - but the set served me damn well for another 10
years.

Interesting that electron guns cathodes ( particularly the red one ) wear
out long before phosphors on the tube face are history.



..... Phil