This TV was bought as DOA and restored to life by replacing the Field
Output chip (a common Hitachi fault, apparently). Now, after some six
months, occasionally (up to twice a day) the lower half of the picture
disappears and is replaced by a bright horizontal line in the middle
of the screen. Switching the TV off immediately and switching it back
on straight away restores the full picture...until the next time.

Is it likely the same component is failing again, or might it be
something else?

Any suggestions welcomed.