LG 520SI, CB550BN BLOCK DIAGRAM

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BLOCK DIAGRAM

CRT

Anode

Focus

Screen

(FBT)

High Voltage

Generation

Circuit

Q301, Q302, Q303, Q304

Q311, Q312, Q313, Q314

Video Output

Circuit

R,G,B R,G,B

Video Drive

R,G,B

Q321, Q322, Q323, Q324

Circuit

MC13281 (IC301)

Vertical Output

Circuit

KA2142 (IC601)

)

DPMS

(IC401)

WT60P1

Mode Control

(

Microprocessor Circuit

Horizontal/Vertical

Drive Circuit

KB2511 (IC701)

D/D Converter

<DDC>

Transformer

(T903)

Secondary Rectifier

Circuit

Control

Switching

Primary

Rectifier

Circuit

7N60A

( IC901)

KA3842B

(Q901)

AC INPUT

DESCRIPTION OF BLOCK DIAGRAM

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1. Primary Rectifier Circuit

This circuit transform AC line voltage to DC voltage as the supplied source for secondary circuit. It is operated by C905 (electrolytic capacitor) and D901, D902, D903, D904 (bridge diode).

2. Switching Control Circuit

This circuit operate to be kept output of the secondary rectified circuit in constant level any conditions; no load, full load, and line voltage variation, ... etc. The main function is operated by the IC901 (KA3842B) syncronizing to horizontal frequency via a connector that tie around the core of the T502 (FBT).

3. Secondary Rectifier Circuit

This circuit rectifying the pulse waveform of the transformer generated by switching control circuit. It is consists of capacitors and diodes. The output voltages are 76V, 55V, 14V, and 6.4V that are necessary to the secondary circuit.

4. Video Pre-Amp Circuit

This circuit pre-amplify the video signal (Red, Green and Blue) to make sufficient signal for the video output circuit. The function is operated by the IC301 (MC13281).

5. Video Output Circuit

This circuit amplifies the video signal which comes from the video pre-amp circuit and amplified video signal is applied to the CDT cathode.

6. Microprocessor Circuit

This circuit generate control signal that need to operating of horizontal and vertical drive circuit, DDC2B (Plug & Play), and DPM (energy saviing) funtion. DDC2B (Plug & Play) function is operated by combination of H/V Sync and SDA/SCL signal.

7. Horizontal and Vertical Drive Circuit

This circuit take function, that are H/V-position, H/Vsize, side-pincushion, and trapezoid, with the output of microprocessor circuit. The generated vertical signal is applied to the vertical output circuit. The generated horizontal signal is applied to the horizontal output and high voltage generation circuit. These are controlled by the IC701 (KB2511) circuit.

8. Vertical Output Circuit

This circuit take the vertical ramp wave from the IC701 (KB2511) and perform vertical deflection by supplying saw-tooth current from the IC601 (KA2142) to the vertical deflection yoke.

9. High Voltage Generation Circuit

This circuit used for generating pulse the primary coil of T502 (FBT). A boosted voltage–about 25kV–appears at the secondary of T502 (FBT) and it is supplied to the anode of the CDT (Cathode Display Tube).

10. Blanking and Brightness Control Circuit.

Blanking circuit eliminate retrace line by supplying negative pulse to the G1 of the CDT (Cathode Display Tube). Brightness circuit is used to control screen brightness by changing the DC level of the G1.

11. D/D Converter.

To obtain constant high voltage, this circuit supplies controlled DC voltage to the FBT and the horizontal deflection circuit according to the horizontal sync frequency.