My parents have a Zenith 35” CRT set I believe it’s model SR3587. The CRT is still in good shape so I would like to save it. I have worked on this set before bad solder connections and caps. My latest problem with this set is the vertical is starting to shrink about an inch both top and bottom. The amount of shrinkage seems to be related to beam current. Horizontal width does not seem to change and is correct. I’m thinking I have bad caps in the vertical or power supply. Unfortunately I don’t have a schematic for this chassis so any help would be appreciated.

Thanks Steve

Look for the Vertical output IC. You'll find it mounted on a heatsink. Replace all the electrolytic caps around the IC. Turning the horizontal width will not effect the vertical. Look for a vertical size control; but, replace the caps first.

Is that chassis on a single PC board or is it they type with a power supply/sweep module on the right and the main module on the left?

It has the two modules sweep on the right and main video on the left. I agree with the checking / changing the caps in the vertical drive / output. I have done that before on this set but that time the size didn't change with beem curent. That's why I felt it may have something to do with sweep/power supply. The high voltage seems to be stable and does not change.