THORN 3000 CHASSIS
The picture keeps pulling (jerking) to the side
at irregular intervals. As it pulls to the side colour is lost and
the picture often breaks up completely for a few seconds.
The fault developed gradually over several weeks – at first
there were periods of several days between jerky spells but
the fault is now there almost constantly. Adjusting the line
hold control gives some improvement but this lasts for only
a few seconds or minutes.
The symptom is called line twitch and can be caused by
several components on the line timebase beard. In order of
likelihood these are as follows: the two 22,uF electrolytics
C506 and C511 in the flywheel
filter and reactance
transistor circuits, the flywheel sync discriminator diodes
W501 and W502, the supply line decoupler C508 (100µF),
and the reactance transistor VT501 (BC183LA).