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The tear is the give away. Your heads are switching there. Old school it was called the PG pulse (Only worked on commercial VTRs). Their is a sensor that tells the electronics where the heads are. It has physically moved or a cap is failing affecting the timing. In older machines there was an adjustment for that. The goal is to have the heads switch in the vertical interval so the noise and timing skew is not seen (forgot what line). This adjustment is typically done with a scope or a cross hatch monitor.
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