THORN 3500 CHASSIS

< Back

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.

Table of Contents

Leave a comment

I have read the privacy policy and accept
Read our privacy policy

This form collects your name, email and content so that we can keep track of the comments placed on the website. For more info check our privacy policy where you will get more info on where, how and why we store your data.

This site uses Akismet to reduce spam. Learn how your comment data is processed.