KB VC1 CHASSIS

This set works well on 405 lines but on switching to 625
lines the field collapses, leaving a horizontal white line
across the screen. The system switching seems to be o.k.
and the scan coils and field output valve have been checked
by substitution.
On 625 lines an extra preset height control R147
(300k52) is added in the feed from the boost rail to the field
charging circuit. Check this control, which is second from
the right at the back of the set.