The trouble on this monochrome portable is white streaking
across the whole screen from any very black picture content, and black streaking from very white picture content.
The fault is present on v.h.f. only, u.h.f. operation being all
This sounds like a form of i.f. instability. We suggest you
check the small ceramic decoupling capacitors such as
C324, C337 and C332 in the i.f. strip, and if necessary the
electrolytics – C314, C333 and C334. It’s possible, though
unlikely, that the v.h.f. tuner or the video output transistor
Q503 could be responsible.