You have to look at whether its over voltage, over current or
no vert sweep causing the HVSD. That will narrow things down.
Keep in mind most of these tests are best done with an analog meter.
On a digital meter numbers are flashing by in the few ms it runs.
Unplug the degauss coil !!
Measure the AC amps at turn on. It should be < 1 amp.
If over its over current
Measure the HV at turn on OR usually the 200V supply to
the 3 video outputs. If high its over voltage.
No vert sweep is best looked at with a scope. It would probably pass the
previous tests.
With that & a CLEAR schematic you can take it further.
good luck
Zeno
LFOD !