LG StudioWorks 500G, Service Manual

DESCRIPTION OF BLOCK DIAGRAM

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,D971,D942) 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
state), voltage of IC401(MICOM) pin 35 come to about
2.5V.
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

function.the data of the adjusted condition is stored in
EEPROM(IC402).

6. Horizontal and Vertical Oscillation

This circuit generates the horizontal pulse and the
vertical pulse by takijg the H and V sync signal.
This circuit consists of the H/V processor(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(T701)). A boosted voltage 9about 24.5V)
appears at the secondary of the FBT and it is suppliesd
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 IC701
and performs the vertical deflection by supplying the
saw-tooth current to the vertical deflection yoke.

13.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.

14.Image Rotation(Tilt)Circuit

This circuit corrects the tilts of the screen by supplying
the image rotation signal to the tilt which is attached
near the deflection yoke of the CRT.

15.Video Pre-AMP Circuit

This circuit amplifies the analog vdeo signal from 0-0.7V
to 0-4V.  It is operated by taking the clamp,R,G,B drive
and contrast signal from the MICOM(IC401).

16.Video Output AMP Circuit

This circuit amplifies the video signal which comes from
the video pre-amp circuit and amplifies it to applied the
CRT cathode.

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