Almost always its the CRT. A LIGHT rejuve will perk things up
but low focus jugs need everything perfect to look good.
I would NOT use a Beltron on it. Its the brute force way.
Beg borrow or steal a modern checker from the 70's up that has
a "clean & balance" setting like a Sencore or B&K.
Also if this is the hybrid chassis watch out for resistors in the hoz osc.
The go up in ohms & eat horz outputs without any symptoms.
73 Zeno
LFOD !