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Early sets will show the jump in horizontal timing at the head-switching point on a VCR. This is because the horizontal AFC time constant is long, which is a good thing for off-air (like a heavy flywheel) to prevent the horizontal phase from jittering left and right under noisy reception conditions. After the introduction of beta and soon thereafter VHS, the time constants were designed shorter so that the horizontal phase could follow the jump within a few lines - but it made the sets also have poorer performance on noisy over-the-air signals. Some of the Zenith designs just before VCRs came in could hold a picture down to a signal strength where only the sync itself was really visible - perhaps going farther than necessary in terms of stability, but guaranteeing good sync on practically any garbage signal.
By the way, the "pull" due to VCRs is only at the top - if you have a pull at the bottom also, it's something else, unless you are seeing the head-switch transient there, in which case, try a different VCR! Also, depending on tape tension, the pull may go either left or right, and sometines it will jump around, a condition known as "flag waving".
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