Look up how a CRT works. As the beam draws picture fields, it moves downwards across the screen driven by a 59.94Hz sawtooth wave. The generator of this sawtooth wave needs to be synced to the vertical blanking interval between fields. “Vertical hold” refers to how long the oscillator waits before the window in which it can accept the sync pulse. Too soon and the picture scrolls down, too late and the picture scrolls up (however, slightly too late, as long as 1/59.94 seconds is still within the window, is fine and the picture can stabilize after one slow scroll up).
Seeing almost two copies of the picture means V-Hold is very late and the vertical oscillator is running way too slow. About 30-40 Hz, very flickery to the person taking the picture!
Look up how a CRT works. As the beam draws picture fields, it moves downwards across the screen driven by a 59.94Hz sawtooth wave. The generator of this sawtooth wave needs to be synced to the vertical blanking interval between fields. “Vertical hold” refers to how long the oscillator waits before the window in which it can accept the sync pulse. Too soon and the picture scrolls down, too late and the picture scrolls up (however, slightly too late, as long as 1/59.94 seconds is still within the window, is fine and the picture can stabilize after one slow scroll up).
Seeing almost two copies of the picture means V-Hold is very late and the vertical oscillator is running way too slow. About 30-40 Hz, very flickery to the person taking the picture!
Ah, thanks for the rundown!