think you already narrowed it down to the horizontal output amp. Maybe early in the amp since the input TP6 is good.

Not sure how you have the scope hooked up but TP4 and TP5 should just be inverted in comparison to each other .

last time I saw this it was the CA3183 IC which is about four ...

when i plug my motorola r2001d i watch just a vertical trace (see picture ) when i select 'scope AC' i have just a spot in screene , i can move this spot in vertical position but no horizontal move when i move horizontal botton .

i test the point TP1 TP4 TP5 TP6 for A2 modul :
TP1 : nice signal ...