Description Of Block Diagram - LG Flatron 774FT Service Manual

1. Line Filter & Associated Circuit
This is used for suppressing noise of power input line
flowing into the monitor and/or some noise generated
in the monitor flowing out through the power input line.
That is to say,this circuit prevents interference between
the monitor and other electric appliance.
2. Degaussing Circuit Coil.
The degaussing circuit consists of the degaussing
coil,the PTC(Positive Temperature Coefficient)
thermistr(TH901),and the relay(RL901).This circuit
eliminate abnormal color of the screen automatically by
degaussing the shadow mask in the CRT during turning
on the power switch.When you need to degaussing in
using the monitor,select DEGAUSS on the OSD menu.
3. SMPS(Switching Mode Power Supply).
This circuit is working of 90~264V AC(50/60Hz).
The operation procecedure is as below:
1)AC input voltage is rectified and smoothed by the
bridge diodes(D900) and the capacitor.
2)The rectified voltage(DC) is applied to the primary
coil of the transform(T901).
3)The control IC(IC901) generates switching pulse to
turn on and off the primary coil of the
transformer(T901) repeatedly.
4)Depending on turn ration of the transformer,the
secondary voltage appear at the secondary coils of the
transformer(T901).
5)These secondary voltage are rectified by each diode
(D941,D951,D961,D962,D9710 and operate other
circuit.(horizontal and vertical deflection,video
amplifer,...etc.)
4. X-ray Protection Circuit
When the high voltage reaches to 29kV in an abnormal
case, tIC401(MICOM) pin 35 sensing from FBT directly.
Then MICOM control IC701 (Deflection controller)to
stophorizontal drive pulse and stop horizontal deflection.
5. Microprocessor Control Circuit
The operating procedure of MICOM(Microprocessor)
and its associating circuit is as fallow:is as follows :
1) Horizontal and Vertical sync signals are supplied
from the signabl cable.
2) Microprocessor(IC401) discriminates the operating
mode from the sync polarity and resolution.
3) The Micom sets operating mode and offers the
controlled data.(H-Size,H-Position,V-Size,...)
4) The controlled data of each mode is stored in itself.
5)User can adjust screen condition by each OSD
functio.tHhe data of the adjusted condition is stored in
EEPROM(IC402).
6. Horizontal and Vertical Oscillation
This circuit generates the horizontal pulse and the

DESCRIPTION OF BLOCK DIAGRAM

vertical pulse by takijg the H and V sync signal.
This circuit consists pof the TDA4841(IC701) and the
associate circuit.
7. D/D(DC to DC) Converter
This circuit supplies DC voltage to the horizontal
deflection output circuit by increasing DC 50V which is
the secdonary voltage of the SMPS in accordance with
the input horizontal sync signal.
8. Side-Pincushion & Trapezoid Correction Circuit
This circuit improve the side-pincushion and the
trapezoid distortion of the screen by mixing parabola
and saw-tooth wave to output of the horizontal
deflection D/D converter which is used for the supply
voltage (B+) of the deflection circuit.
9. Horizontal Deflection Output Circuit
This circuit makes the horizontal deflection by supplying
the saw-tooth current to the horizontal deflection yoke.
10. High Voltage Output & FBT(Flyback Transformer)
The high voltage output circuit is used for generating
pulse to the primry coil of the FBT(Flyback Transformer
)secondary of the FBT and it is supplied to the
anode,focus,and screen voltage of the CRT.
11. H-Linearity Correction Circuit
This circuit corrects the horizontal linearity for each
horizontal sync frequency.
12. Vertical Output Circuit
This circuit takes the vertical ramp wave from the
TDA4841(IC701) and performs the vertical deflection by
supplying the saw-tooth current to the vertical deflection
yoke.
13. Dynamic Focus Output Circuit
This circuit takes the horizontal and the vertical
parabola waves from the TDA4841(IC7010 and
amplifies it to maintain constant focus on center and
corners in the screen.
14. H & V Blanking and Brightness Control
Blanking circuit eliminate retrace line by supplying
negatinve pulse to the G1 of the CRT.And Brightness
circuit is used for control of the screen brightness by
changeing DC level of the G1.
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