THORN 3500 CHASSIS
The set works normally for an hour or longer, then picture
jitter sets in. This may clear for a while, or alternatively the
picture may disolve into a moving jumble of coloured lines.
Again a normal picture may return — if one has patience!
There are several causes of horizontal jitter on the
Thorn 3000/3500 chassis. In order of likelihood, these are as
folows: the line generator supply decoupler C508 (100,uF);
the 22 or 25 uF electrolytics C506 and C511 in the flywheel
sync filter and reactance stages; the reactance transistor
V1501 (BC183LA); and the flywheel sync discriminator
diodes W50 1/W502 (type Y728 — BY206s can be used).