The vertical output IC has stopped working. The vertical output IC is the part that drives the coils in the yoke that spreads the picture up and down. This could be because it has cracked loose from the board (solder joints) or it simply burned out. Sometimes a bad pump-up cap will cause the vertical output IC to short out, and when the IC shorts out it often opens up a small value resistor next to the flyback. This is a relatively easy thing to repair. A qualified tech will be able to tell exactly why the vertical output has stopped working and repair it for you.
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