RCA New Vista

[Old1625]

Bear in mind that the vertical size control can also affect linearity. Both controls need to be tweaked alternately, until you can be sure the top and bottom edges of the raster are just off the screen phosphor, and that the lines are evenly spaced from top to bottom. This takes a bit of practice.

If no combination of adjustments of the 2 controls corrects the problem then the vertical oscillator/output tube(s) would bear examination and replacement as needed.

If none of the above correct the problem then you need to go deeper into the circuitry and check for capacitors becoming leaky or changing value out of tolerance. Resistors need to be checked as well.