Dave...he didn't turn the set off...it was broken up by static, if you'll
go back and look, because a much stronger transmission was coming in.
Namely, the one that appeared in his room. If you'll note, it goes away,
THEN, puzzled, Sinclair goes to the screen to see why it's gone.
It is, as you say, "very annoying" to be accused of a "standard TV
cliche" that in fact only happened in the viewer's memory.