THORN 3500 CHASSIS

There seem to be several problems with this set. First, when
the picture content darkens, the picture takes on a greenish
tint and shrinks by about three-quarters of an inch all
round. This reverts to normal when the picture brightens.
There’s cramping on the right-hand side of the screen – adjusting the line linearity coil makes no difference. I changed the line output transistor and then tried to set up the beam
limiter, but the picture is very dark and the voltage across
R907 in the beam limiter circuit is over 5V.
Your problems all stem from the excessive voltage across
R907 (should be 1.3V with the screen blacked out). First
ensure that R907 (1.5Q) hasn’t changed value – replace it if
in any doubt. If the high voltage across it remains, the fault
is excessive loading in the line output stage. Progressively
disconnect the tripler, the shift choke L504, the first anode
supply rectifier W505, the scan coils etc. When the correct
voltage across R907 returns, you’ve found the faulty component. If the overload persists however, the line output or
e.h.t. transformer is suspect.