64 Zenith

[VA561]

I have a '64 Zenith console, the "Chancellor" model. When I first turn the set on, there is about a 1" gap at the bottom of the screen. After the set warms up for a few minutes, the raster pretty much fills in the screen. Any thoughts on what could be causing the bottom gap? I have tried tweaking the vert centering and height adjustments. Could there be another issue instead of the vert adjustments? Just curious. The set has a pretty good picture as I type this post.