Description Of Block Diagram - LG STUDIOWORKS 77M 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 this monitor flowing out through the power input line.
That is to say, this circuit prevents interference
between the monitor and other electric appliances.
2. Degauss Circuit & Coil.
The degauss circuit consists of the degaussing coil,
the PTC(Positive
thermistor(TH901), and the relay(RL901). This circuit
eliminates abnormal color of the screen automatically
by degaussing the shadow mask in the CRT during
turning on the power switch. When you need to
degauss 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 procedure is as follows:
1) AC input voltage is rectified and smoothed by the
bridge diodes (D901~D904) and the capacitor
(C907).
2) The rectified voltage(DC) is applied to the primary
coil of the transformer(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 ratio of the transformer, the
secondary voltages appear at the secondary coils
of the transformer(T901).
5) These secondary voltages are rectified by each
diode(D902, D922~D924, D926, D927) and
operate other circuit. (horizontal and vertical
deflection, video amplifier, sound, ...etc.)
4. X-ray Protection.
If the high voltage of the FBT reaches up to 29kV
(abnormal state), Q807 operates and IC401(MICOM) pin
11 come to low level. Then MICOM control IC701
(Deflection controller) to stop Horizontal drive pulse and
stop Horizontal Deflection.
5. Micom(Microprocessor) Circuit.
The operating procedure of Micom(Microprocessor)
and its associated circuit is as follows:
1) H and V sync signal is supplied from the signal
cable.
2) The Micom(IC401) distinguishes polarity and
frequency of H and V sync.
3) The Micom sets operating mode and offers the
controlled data. (H-size, H-position, V-size, ... etc.)
4) The controlled data of each mode is stored in itself.

DESCRIPTION OF BLOCK DIAGRAM

Temperature Coefficient)
5) User can adjust screen condition by each OSD
function. The data of the adjusted condition is
stored in EEPROM(IC402).
6) Users can control screen condition by the OSD,
Select, Right, Left, Audio, Audio Mute buttons, and
Brightness, Contrast volume.
6. Horizontal and Vertical Oscillation.
This circuit generates the horizontal pulse and the
vertical pulse by taking the H and V sync signal.
This circuit consists of the TDA4856(IC701) and the
associated circuit.
7. Oscillating Circuit for D/D Converter.
This circuit generates the saw-tooth wave which has
the horizontal period by taking output of the
TDA4856(IC701).
8. D/D(DC to DC) Converter.
This circuit supplies DC voltage to the horizontal
deflection output circuit by decreasing DC 160V which
is the secondary voltage of the SMPS in accordance
with the input horizontal sync signal.
9. Side-Pincushion & Trapezoid Correction Cirucit.
This circuit improves 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.
10. Horizontal Deflection Output Circuit.
This circuit makes the horizontal deflection by
supplying the saw-tooth current to the horizontal
deflection yoke.
11. High Voltage Output & FBT(Flyback Transformer).
The high voltage output circuit is used for generating
pulse to the primary coil of the FBT(Flyback
Transformer (T701)). A boosted voltage(about 26kV)
appears at the secondary of the FBT and it is supplied
to the anode, focus, and screen voltage of the CRT.
12. H-Linearity Correction Circuit.
This circuit corrects the horizontal linearity for each
horizontal sync frequency.
13. Vertical Output Circuit.
This circuit takes the vertical ramp wave from the
TDA4856(IC701) and performs the vertical deflection
by supplying the saw-tooth current to the vertical
deflection yoke.