Repair manual

2-61
THEORY OF OPERATION
Note
This principle is based on the rule in
electricity and electronics that like poles
repel and unlike poles attract.
After the stream of electrons is focused into a beam and accelerated, it
speeds toward the display screen of the CRT. A high positive anode
voltage attracts the beam towards the display screen.
The inner section of the display screen is coated with phosphor, and when
the accelerated beam strikes the phosphor coating, the phosphor fluoresces
and emits light.
The phosphor has a degree of persistence. That is, the glow that results
persists for a small interval of time even after the beam of electrons dies
down or moves away from its original location.
The ability to hold a glow for a short interval of time is valuable because
it permits the beam to leave a trace as it moves across the display screen.
For example, if the electron beam starts at the left side of the CRT and
moves rapidly to its right, a straight-line visible glow appears. By having
the electron beam shoot across the display screen from left to right in
rapid succession, the process know as scanning occurs. This process
literally paints an image on the display screen.
The combined functions of the horizontal and vertical deflection circuits
produce an image on the display screen.
The horizontal deflection circuit processes the horizontal sync (MONHS)
signal from the Logic Controller P.C. Board. It generates a flyback pulse
that drives the horizontal yoke causing the CRT beam to move
horizontally across the display screen.
The vertical deflection circuit processes the vertical deflection
(VDEFLECT) signal from the Logic Controller P.C. Board. It generates
an output signal that drives the vertical yoke causing the beam to deflect
down one scan line.
Timing is essential to the combined effort of both circuits to synchronize
the image on the CRT.