Television sets used to have vertical and horizontal hold control knobs that could be adjusted by the user to stop the picture from rolling. These adjustments were occasionally necessary before more advanced electronics rendered them obsolete. The vertical or horizontal hold on an old TV might fail for several reasons.
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Older television sets used individual resistors that tended to get hot and "drift" off their designed resistance with age or prolonged TV use. An overheated or damaged resistor might make the picture roll.
The picture tube contains a "gun" that fires high-speed electron beams at the screen where phosphors convert them to visible light. Vertical and horizontal synchronisation circuits keep the picture centred and steady on the screen. A maladjusted vertical sync will allow the picture to roll even if the user adjusts the hold knob. A picture pushed to one side of the screen is sign of a defective horizontal sync circuit.
An oscillator repeats a process. The TV electron gun scans from the top to the bottom of the screen by rows 60 times per second. This oscillation it is not visible to the naked eye. An image that does not vertically fill the screen might signal a defective vertical oscillator. Side-to-side rolling which cannot be corrected is a telltale sign of a horizontal oscillator failure. These circuits contain several components including transistors, simple integrated circuits and filters. Older TVs may require a tube replacement.
Smaller, old televisions tended to have simpler and less expensive controls. Sometimes the vertical or horizontal hold control didn't have a maximum or minimum "stop" setting, so it could be turned too far and unscrew itself. A small coil inside the control physically falls out in such cases and it must be reassembled for the control to work.
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