LG CB20T20X 20 inch color television – how to enter the service mode, service mode adjustments, circuit diagram

 

Used ICs: TDA2006, TDA8841 or TDA8842, U4488B, LA7016, CD4052B, SAA5281, CXP864P61S, 24C16, TDA8351, STR S5707, TDA6107Q, GMS30140 [remote control IC]

To enter the service mode press "OK" buttons on both TV set and the Remote control at the same time.

RF AGC (Automatic Gain Control) Adjustment

Test Point : AGC TP (J05)

Adjust : Remote Control.

The RF AGC was aligned at the time of manufacture for optimum performance over a wide range conditions.  Readjustment of RF AGC should not be necessary unless unusual local conditions exist, such as;

1) Channel interference in a CATV system.

2) Picture bending and/or color beats, which are unusually due to excessive RF signal input when the receiver is too close to a transmitting tower or when the receiver is connected to an antenna distribution system where the RF signal has been amplified. In this case, the input signal should be attenuated (with pad or filter) to a satisfactory level.

3) Picture noise caused by "broadcast noise" or weak signal.  If the broadcast is "clean" and the RF signal is at least 1mV (60dBu), the picture will be noise free in any area.

Adjusting RF AGC to one end of rotation will usually cause a relatively poor signal to noise ratio;

Adjusting to the other end of rotation will usually cause a degradation of over load capabilities resulting in color beats or adjacent channel interference.

Adjustment

1. Connect RF signal (65dB!0.2dB) and turn on the TV.

[Standard adjustment Channel]

- EU 05 Ch. (frf = 175.25MHz) : CK, CL, CB

- EU 41 Ch. (frf = 631.25MHz) : CI

2. Press OK buttons on TV set and Remote Controller at the same time to get into SVC-0 mode.

3. Press Channel UP/DOWN button on the Remote Controller several times to find AGC?

4. Press Volume UP/DOWN button until the AGC Voltage is the same as the Table below.

5. Press OK(Y) button to memorize the data.

Screen Voltage Adjustment

Test Point : RK (Red Cathode of CPT Board)

Adjust : Screen Control of FBT

1) Press TV/AV Key to get AV Mode.

2) Connect the probe of oscilloscope to the RK (Red Cathode) of CPT Board.

3) Adjust Screen Volume of FBT so that the waveform is the same as below figure.

Focus Adjustment

Test Point : Observing Display

Adjust : Focus control of FBT

1) Tune the TV set to receive an inactive channel station.

2) Adjust the Focus control of FBT for best overall focus.

Deflection Data Adjustment (Line SVC-1)

Enter the service mode as described earlier.

1. Preparation for Deflection Adjustment

1) At SVC mode, press the Yellow colored button.

If the Remote Controller doesn't have the Yellow button, you should use a Service Remote Control (105-201G) and press SVC button.

And then, deflection data adjustment OSD (SVC1 mode) will be displayed.

2) Press Channel UP/DOWN button for desired function Adjustment.

3) Press Volume UP/DOWN button to adjust the data.

2. Deflection Adjustment Procedure

1) Vertical Adjustment

Select VS and adjust until the mechanical center of CPT and that of screen coincides and select VA and adjust to coincide the inner circle of screen with outer frame of CPT

2) Horizontal Adjustment

Select HS and adjust until the mechanical center of CPT and that of screen coincides.

3) Vertical S Correction Adjustment

Select SC and adjust until top-bottom side pincushion is equal.

4) Press OK button to memorize the data.

White Balance Adjustment.(LINE SVC-0)

NOTE : This adjustment should be performed after screen voltage adjustment.

1) Tune the TV set to receive an 100% white pattern.

2) Press OK(Y) buttons on TV set and remote controller at the same time to get into SVC mode.

3) Press PSM(RED) button on remote controller. (Standard picture)

4) Press Channel UP/DOWN button for desired function adjustment.

5) Adjust VOL+ or VOL- button for GG031.

6) Adjust VOL+ or VOL-button in each status of "Rg--"/"Bg--" for X=293!8, Y=295!8 with color analyzer.

7) Press OK(Y) button to memorize the adjustment data.

OPTION Adjustment (SVC MODE:OPTION-1, OPTION-2)

NOTE: When the EEPROM has been replaced, the Option data should be restored as the function of individual system and specification.

1) Press OK buttons on both TV set and Remote Controller at the same time to get into SVC mode.

2) Press the Yellow button several times to find OPTION-1 or OPTION-2.

3) Input the correspond OPTION data referring to Table below with the numeric buttons 0~9

Exploded view

Main board

Circuit diagram [Schematic] – PC-81A chassis