Toshiba hi-def CRT black bar

[zeno]

I would suspect a little surface mount cap is bad & there are
tons of them in there. Try this.
Be SURE the closed captioning
is turned OFF it can do odd things on older sets including a
black box that comes & goes.
Open set & lightly poke around where any boards plug in.
You may get lucky there.
The set probably digitalizes the analog signal & everything goes
through a board with one or more huge surface mount IC's.
Odds are its on that. You can try freeze mist on the board a
very small area at a time. Also look for anything amiss there.
Just before we closed we had a 36' Sony CRT HDTV that
had a very similar problem but it acted up once a week.
We junked it. Boards are VERY expensive to gamble on.
Good luck

73 Zeno