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On the first trace, the scope is synced at horizontal rate. On the second, if you didn't change the sweep rate, the scope has lost sync.
You need to set the sweep rate to vertical rate, and look for the pulses in the first few scan lines of the signal after vertical sync. You can compare which lines the pulses are on from the cable box to which ones they are on from a DVD player, for example.
[edited a few typos]
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Old TV literature, New York World's Fair, and other miscellany
Last edited by old_tv_nut; 03-28-2015 at 11:01 PM.
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