I've got a NEC Multisync-II VDT (JC-1402HMA), about 10-15 years old.
Brightness and contrast are OK, not stunning. But when cold, it's badly
out of focus and becomes acceptable after ~10 minutes as it warms up. I
can twiddle the focus adjustment to get good focus when cold but then
focus is bad when warm. Brightness/contrast don't appear to change much
as it warms up.

Is there any particular component or two which would fix the problem?
I've got the service manual so I won't be totally in the dark.

Thanks