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Picture 2 and 3 appear to show differentiated pulses. This would imply poor low frequency response. Vertical sync needs the lower frequency response to work properly.
Perhaps poor low frequency response in the video amplifier is the culprit. It could be due to bad (low capacity) coupling capacitors or open screen decoupling or cathode bypass capacitors.
The RF/IF response could also be the cause: if the video carrier is too low on the nyquist slope of the IF response or if the IF or RF response is not correct, the low frequencies would be attenuated. To check this out, simply adjust the fine tuning control where the color disappears and when the video begins to get a bit smeary. If the interlace improves, that may be it.
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