I dont know your level so dont take this wrong !
Primary side ( hot) ground for your meter is the negative end of C011. Use it
for measurements on the RIGHT side of the SMPS transformer.
The chassis ( cold) ground is the tuner & IF shields, CRT dag etc.
The left side of transformer windings are the only cold grounds.
The isolator is to feed back the cold B+ to the hot side for a reference voltage
to control the PS output.
In the olden days we saw quite a few of these. If the transistor was OK we
would change the 2 modules & isolator. This fixed almost every one.
If you have a variac you can try turning it up & down a bit & see what happens.
Enuf fer now
Zeno
LFOD !