Wow, wish everyone worked a problem like this ! Well done.
If you have an anylist break the chain at the video amp & inject
video. This will cut the possible stages in half. Its why I scream
" learn the block diagram" for newbies.
I would not suspect the CRT. Those little square peaking coils
did open but I never saw one short. I am sure you covered it
but be sure all the ground lugs for the PCB's are good & any shielding
like the IF is also.
On the Sencore most of there gear came with 2 manuals. One was
a basic manual & the other was a large book that showed every
creative thing you can do with it. Look into that.
73 Zeno
LFOD !