Editing Analog television (section)

=== Horizontal and vertical hold ===
The sweep (or deflection) oscillators were designed to run without a signal from the television station (or VCR, computer, or other composite video source). This allows the television receiver to display a raster and to allow an image to be presented during antenna placement. With sufficient signal strength, the receiver's sync separator circuit would split timebase pulses from the incoming video and use them to reset the horizontal and vertical oscillators at the appropriate time to synchronize with the signal from the station.

The free-running oscillation of the horizontal circuit is especially critical, as the horizontal deflection circuits typically power the [[flyback transformer]] (which provides acceleration potential for the CRT) as well as the filaments for the high voltage rectifier tube and sometimes the filament(s) of the CRT itself. Without the operation of the horizontal oscillator and output stages in these television receivers, there would be no illumination of the CRT's face.

The lack of precision timing components in early equipment meant that the timebase circuits occasionally needed manual adjustment. If their free-run frequencies were too far from the actual line and field rates, the circuits would not be able to follow the incoming sync signals. Loss of horizontal synchronization usually resulted in an unwatchable picture; loss of vertical synchronization would produce an image rolling up or down the screen.

Older analog television receivers often provide manual controls to adjust horizontal and vertical timing. The adjustment takes the form of ''horizontal hold'' and ''vertical hold'' controls, usually on the front panel along with other common controls. These adjust the free-run frequencies of the corresponding timebase oscillators.

A slowly rolling vertical picture demonstrates that the vertical oscillator is nearly synchronized with the television station but is not locking to it, often due to a weak signal or a failure in the sync separator stage not resetting the oscillator.

Horizontal sync errors cause the image to be torn diagonally and repeated across the screen as if it were wrapped around a screw or a barber's pole; the greater the error, the more copies of the image will be seen at once wrapped around the barber pole.

By the early 1980s the efficacy of the synchronization circuits, plus the inherent stability of the sets' oscillators, had been improved to the point where these controls were no longer necessary.  Integrated Circuits which eliminated the horizontal hold control were starting to appear as early as 1969.<ref>{{cite web |last1=Mills |first1=Thomas |title=A five function IC for television receivers |url=https://www.researchgate.net/publication/3478408 |website=ResearchGate |publisher=IEEE |access-date=11 May 2019}}</ref>

The final generations of analog television receivers used IC-based designs where the receiver's timebases were derived from accurate crystal oscillators. With these sets, adjustment of the free-running frequency of either sweep oscillator was unnecessary and unavailable.

Horizontal and vertical hold controls were rarely used in CRT-based computer monitors, as the quality and consistency of components were quite high by the advent of the computer age, but might be found on some composite monitors used with the 1970s–80s home or personal computers.