Thats a weird symptom. Never seen a yoke short in a modern set
& give a key stone pattern. Bad yokes are super rare on solid state
sets. Out of thousands I may have seen 10 & most were on GE's.
I would look at the power supply 1st. A good chassis pix will
show who built it & maybe a few more ideas. A model ## too !
73 Zeno
LFOD !