99% sure it is the picture tube.
Very Very Very common failure mode on Sony sets with AKB, especially certain
vintage 32" tubes. Since you are also losing OSD the tube is being blanked
out.
You can confirm by VERY slightly turning up the G2 voltage to the tube when
it is blanking out, if the blanking stops and solid video is restored, the
tube failure is confirmed.

If it were a more solid failure like the vertical circuit failing, it would
have gone out completely by now and would not likely get better when the set
is warm but worse.

David

Russ Wright *NO*SPAM* wrote in message
...
The screen goes to "black", then the video returns ,does not matter what
video source or VHF , the menu as well disappears. The audio is not
affected

It seems to become better after a hour , meaning the video stays on

Will look for possible cold solder joints, any other suggestions

Russ