LG T910B, Service Manual

Page: 16 / 43

DESCRIPTION OF BLOCK DIAGRAM
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1. SMPS(Switching Mode Power Supply)
When you turn on the power switch, the operating
procedure is as follows:
1) The AC line voltage is rectified by the bridge diode
D901.
2) The control IC(IC901) starts switching and generates
switch pulse in the primary turn of the SMPS
transformer(T901)
3) The switching pulses of the primary turns are induced
to the secondary turns of the transformer by the turn
ratio. This pulses are rectified by each diode(D924,
D923,D922,D921,D920)
4) Each rectified DC voltage(80V, 50V, 15V,12V, 6.3V
5V and -12V)
2. Over Voltage Protection Circuit
When the input of IC901 Vin(pin 4) is more than
22V, all the secondary voltages of the SMPS
transformer (T901) down to low value
3. Display Power Management Circuit(DPM)
1) STAND-BY & SUSPEND Mode
When no input of horizontal or vertical sync Q951,
Q941 are turned off and Q912,Q914 are turned off.
Then input power consumption is below 8 watts.
2) OFF Mode
When no input of horizontal and vertical sync Q951,
Q941 are turned off and Q912, Q914 are turned off.
Then input power consumption is below 3 watts.
4. Microprocessor Control & Horizontal and
Vertical Sync Processor Circuit
The operating procedure is as follows ;
1) There is Horizontal & Vertical process function in
Microprocessor.(IC401)
2) Microprocessor (IC401) discriminates the operating
mode from the sync polarity and resolution.
3) After microprocessor reads these adjusted mode data
stored at EEPROM, it controls operating mode data
through IIC
4) Users can control screen condition by the OSD Select,
Up, Down, Left, Right.
5) The horizontal and vertical sync processor IC (IC401)
has a sync detector, a saw-tooth generator, and drive
function, And outputs horizontal and vertical drive
signal to control screen distortions
5. D/D Converter Circuit.
To obtain constant high voltage, this circuit supplies
controlled DC voltage for FBT and horizontal deflection
circuit according to the horizontal sync frequency.
6. X-RAY Protection Circuit
When the high Voltage reaches to 30kV in an abnormal
case, the high voltage detector circuit, R818,D721,C739,
R416, R417,C409 start operation to shut down high
voltage circuit.
7. Horizontal S-correction Circuit.
This circuit corrects the horizontal linearity for each
horizontal sync frequency.
8. Horizontal drive and Output Circuit.
This circuit is a horizontal deflection amplifier for raster
scan.
9. ABL Circuit
This circuit limits the beam-current for the reliability of
CDT
10. Vertical Output Circuit
This circuit takes the vertical ramp wave from the
TDA4867J (IC601) and perform the vertical deflection
by supplying the saw-tooth wave current to the vertical
deflection yoke.
11. Blanking and Brightness Control Circuit.
Blanking circuit eliminates the retrace line by
supplying a negative pulse wave to the G1 of the CDT.
Brightness control circuit is used for control of the
screen brightness by changing the DC level G1.
12. Image Rotation (Tilt) Circuit.
This circuit corrects the tilt of the screen by
supplying the image rotation signal to the tilt coil
which is attached near the deflection yoke of the
CDT
13. OSD (On Screen Display) Circuit.
This circuit displays information of the monitor`s status
on the screen.
14. Degauss Circuit & Coil.
The degauss circuit consists of the degaussing coil,
the PTC (Positive Temperature Coefficient) thermistor
(TH901), and the relay (RL901). This circuit eliminates
abnormal color of the screen automatically by
degaussing the slot mask in the CDT when turn on the
power switch.
When you need to degauss while using the monitor,
select DEGAUSS on the OSD menu.