Asimov wrote:
Basically this symptom mimics what arcing would do, which is to inject
high voltage glitches into the horizontal output section. Other
circuits that handle high voltages are the focus and screen controls.
If one of these has an intermittant contact it would seem like arcing
too. Same thing with the neck board crt socket since this carries the
actual voltages to the tube and any intermittant here would also seem
like arcing. Clean the crt pins with a plastic scotchbrite pad.
Similarly the wire connectors on the main board for these voltages may
be iffy. Even the crt high voltage cup is a suspect, clean and use
dielectric grease to seal the air out of the high voltage rubber boot.
Don't forget to discharge the crt first just in case!
a lot of other useful information

Now this is what I came here for, and then some! Thank you Asimov. Now I
have something very concrete to go by. If you ever visit Finland, look me up
and you shall not be short of beer.

--

Arto Rantala