Interesting symptoms. Almost looks like HVSD but usually that
will kill the set & latch it off until power reset.
1) post just the schematic.
2) check for cold solder joints especially the horz out & flyback area.
3) look for an electrolytic cap associated with the ON/OFF relay coil
power supply.
Odds are it should be an easy fix but take your time & stay on track.
73 Zeno
LFOD !