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Overall Block Diagram
A TV set consists of several stages or blocks:
•
Power Supply
•
Power On/Communications
•
Video Processing
•
Deflection
Each stage has a purpose and is activated in sequence to properly power
up the set.
Power Supply
The purpose of the power supply is to convert the incoming 120Volts AC
to some of the DC voltages required to operate the set, the most impor-
tant of which is the Standby +5Vdc. Standby +5Vdc is present when the
set is plugged in and is used to power the Micro so it can respond to a TV
power ON command from the user.
Power On/Communications
Three things occur when the power button is pressed:
•
Degaussing of the picture tube
•
Application of power to the Jungle IC
•
Data communications
When the TV is powered ON, the Micro turns ON the degaussing circuit
for 2.2 seconds. Its purpose is to pass AC through the degaussing coil
that surrounds the picture tube. The AC field that is created erases re-
sidual magnetism collected by the tube's metal aperture grill.
Next the Micro IC turns the TV ON switching power from the power sup-
ply to the Y/C Jungle IC. The Jungle IC produces vertical (VD) and hori-
zontal (HD) pulses to create the remainder of the voltages necessary for
the TV to operate. This turns ON the TV (see Deflection).
After the TV turns ON, data and clock communications from the Micro IC
are applied to the tuner and Jungle IC. The tuner is instructed to tune to
15
the last station viewed and the Jungle IC is instructed to select the last
video input used before the set was turned OFF.
The communications data and clock lines are always active when the TV
is ON.
Video Processing
The Y/C Jungle IC selects a video signal from one of two external video
inputs or the internal tuner video for processing. Contrast, brightness,
color level and hue are also controlled in this IC. A change in level is
received by the Micro IC, stored in memory, and communicated to this Y/
C Jungle IC thorough the data and clock inputs. The final stage within
this IC converts the information to individual red, green and blue (RGB)
output voltages. The higher the voltage, the greater the intensity of that
color. The three RGB voltages are applied to the video output stage.
The purpose of the video output stage is twofold:
1. To invert the signal
2. To convert the small red, green and blue input voltages to larger volt-
ages for the picture tube drive
The voltage output of this video stage is applied to the picture tube cath-
odes. This voltage varies from 200 volts for a dark picture to zero volts
for a very bright picture.
Deflection
When the Y/C Jungle IC receives power and serial data, its internal ver-
tical and horizontal oscillators operate and output. These two VD and
HD signals leave the IC to drive the external deflection amplifiers. The
output of the vertical deflection stage drives the vertical deflection coil of
the yoke. The purpose of the vertical yoke coil is to move or "sweep" the
picture tube's electron beam downward to produce the picture.
The yoke and flyback transformer (FBT) use the output of the horizontal
deflection stage. The yoke uses this drive signal in the horizontal deflec-
tion coil to sweep the electron beam from left to right and back (retrace)
to produce the picture.
The flyback transformer is a low current high frequency transformer
that develops the remainder of the voltages the TV set needs to oper-
ate.
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