LG MC994A Service Manual

- 1 -

Y Safety Precautions

1. It is safe to adjust after using insulating transformer between the power supply line and chassis input to prevent the risk of electric shock and protect the instrument.

2. Never disconnect leads while the TV receiver is on.

3. Don't short any portion of circuits while power is on.

4. The adjustment must be done by the correct appliances. But this is changeable in view of productivity.

5. Unless otherwise noted, set the line voltage to 230Vac!10%, 50Hz.

Y Test Equipment required

1. RF signal generator (with pattern generator)

2. DC Power Supply

3. Multimeter (volt meter)

4. Oscilloscope

5. Color analyzer

RF AGC (Automatic Gain Control) Adjustment

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.

: Screen Voltage Adjustment

1) Input the Color Bar Pattern into Antenna jack.

2) Select CutOff of SVC-3 mode.

3) Turn the screen control clockwise until the Horizontal line is visible and turn it counterclockwise until the Horizontal line is faintly visible.

: Focus Adjustment

NOTE: This adjustment should be performed after warming

up for 10 minutes.

1) Input the Color Bar Pattern into Antenna jack.

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

: VCO Adjustment

1) Input Digital Pattern into Antenna jack.

2) Select A-PIF of SVC-4 mode.

3) Press VOL

F/G button and A-PIF will be changed 0 to 1

while the number of PIF-C is rolling.

4) When PIF-C stops rolling, A-PIF will be changed 1 to 0 and VCO adjustment is finished.

Caution : Do not press the Volume button again in A-PIF mode

after adjustment is finished.

Adjustment

1. Connect RF signal (65dB!0.5dB) and turn on the TV.

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

1. To get into SVC mode

1) Press OK buttons on both TV set and Remote Control at the same time.

2) Press Yellow button to select OPTION-1, OPTION-2, OPTION-3 or OPTION-4.

3) Press PR E/D button to select an adjustment.

4) Press VOL F/G button to change the data.

2. To memorize the adjusted data into EEPROM

Press OK button.

3. To get out from SVC mode

Press TV/AV or Power button.

Test Point : AGC TP (J17) Adjust : Remote Control

Test Point : RK (Red Cathode of CPT Board) Adjust : Screen Control of FBT

TUNER

AGC Voltage

Default AGC Data

6700VPV002A(LG C&D)

2.5

0.1V

6700VPV002B(LG C&D)

3.0

0.1V

Test Point : Observing Display Adjust : Focus control of FBT

ADJUSTMENT

- 2 -

: Deflection Data Adjustment (Line SVC-2)

1. Preparation for Adjustment

1) Select SVC-2 Mode.

2) Tune the TV set to receive Digital Pattern and set ARC Mode to Standard.

2. Initial deflection data and average data for CPT

3. Adjustment

1) VL(Vertical Linearity) Adjustment

Select VL adjustment mode to adjust the upper and lower vertical size to be the same for horizontal center line.

2) VS(Vertical Shift) Adjustment

Adjust the geometrical horizontal center line of the screen to be coincided with the vertical center line of CPT.

3) VA(Vertical Amplitude) Adjustment

Adjust the upper and lower part of big circle of the received pattern to be placed on 6~7mm from the valid screen.

4) HS(Horizontal Shift) Adjustment

Adjust the geometrical vertical center line of the received screen to be coincided with the horizontal center line of CPT.

5) SC(Vertical S Correction) Adjustment

Adjust the width of upper/center/lower grid of the received pattern to be the same.

: SECAM Background Color Adjustment(CT-, CF-)

1. Preparation for Adjustment

Select ÒS R-YÓ or ÒS B-YÓ of SVC Mode 4.

2. Adjustment

While switching SECAM and PAL channels in turns, press VOL F/G key until the background color of SECAM channel to be the same as that of PAL Pattern at S R-Y or S B-Y.

: White Balance Adjustment.(LINE SVC-1)

NOTE : This adjustment should be performed after screen voltage

adjustment.

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

2) Select SVC-1 Mode.

3) Press PR UP/DOWN key to select BG, GG, BG, GC. Adjust BG, GG on Brightness 40!

1FL and BG, GC on

Brightness

4.5!

0.5FL with VOL

F/G

key to get the color value.

Adjust BG, GG from the initialized data to get the color value of X=281

8, Y=288!8.

5) R,G,B initial data and average data

: Sub Brightness Adjustment

NOTE: This adjustment should be performed after White

Balance adjustment.

1) Input FUBK pattern to Antenna jack.

2) Select S-BRI of SVC-3 mode.

3) Press VOL F/G until (a) and (b) of FUBK are distinct and press VOL G twice more.

: 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.

Status

Initial Data

127

147

123

Remark

Status Default

21" LG

20" LG

14" LG

(a) (b)

- 3 -

Table 1. OPTION 1 Function

Table 2. OPTION 2 Function

Single SYSTEM(CA-)

South East Asian DUAL

W/O RF 3.58(CF-,CZ-)

W/RF 3.58(CT-,CD-)

with RGB Input

EYE

TOP

H-TONE

4 KEY

SCART

CCTV

SYSTEM

Option Code

Function Remark

BG Only

BG+TAI DUAL

BG+I+DK

BG+I+DK+M

W/O CCTV

W/CCTV

Phono Jack or Camera-in Jack

Scart Jack

6 Key(MENU, OK, VOL-, VOL+, PR-, PR+)

4 Key(TV/AV, ROTATE, PR-, PR+)

W/O EYE

W/EYE

Teletext Top function Disable

Teletext Top function Enable

Blue Background OSD MENU

Half Tone OSD MENU

LG8993-27A/B

LG8993-28A

LG8993-29A

CURVE

TBS

HOTEL

LANGINDEX

LANG.

Option Code

0 0

0 1

1 0

Function Remark

Multi

English Only

TWO Lang.

English

CIS

China

Romania

Poland

English

France

Hindi

Arab

Urdu

Parsi

English

Indonesia

Malay

Vietnam

Thai

Fast Volume Curve

Slow Volume Curve

TBS Function Disable

TBS Function Enable

HOTEL Function Disable

HOTEL Function Enable

BLOCK DIAGRAM

Video

SECAM TA 1275Z

13 153 5

R-Y B-Y C Y-in

Y-out

VCD 1 Chip TB1238BN

B+

9V REG

ST 5V

AUDIO B+

Power Input

110 - 240Vac

30V

12V

14V

MICOM

AGC

IF - in

Pre-AMP

4.5M Others

SAW Filter

AGC

26V

Head phone

Speaker

RGB-out

RGB

187V

Ver. AMP.

LA7833

V-DY

RGB

CVBS

Col.

H-DY

H-out

H.D.TR

OSD RGB

E2PROM

PreAMP

Local

KEY

RGB (Scart only)

(Scart or Phone)

SIF

Trap

Y-in Video

out

5.5

6.0

6.5

4.5

SIF

Audio-out

CPT

C LINE

TUNER

LNA on off

(from Micom)

RGB

CPT Board

SMPS Trans.

S0 / S1

Audio SW CD4052B

3739

TELETEXT(Euro) SAA5281Z

112V (14Ó/20Ó) 115V (21Ó)

V-out

B+

FBT

Video

Monitor

Out

RGB SW

TEA 5114A

EXT RGB

(from SCART)

MICOM

Sound Amp.

TDA7253

SIF

Filter

5.5

6.0

6.5

4.5

Ext.

Video

A / V SW LA7222

Picture

Picture (from Camera)

(from AV ) Video

Ext.

Audio

(FRONT)

Audio

Video

Camera

Monitor SW

LA7016

Audio

(Scart or Phono)

Optional

Parts

(from AV )

Audio

12 Melody

(from Micom )

(from AV) Audio

Trans

37,38

10,9

42,41,40

16,17,18

RGB

CVBS

TELETEXT(Parsi) SAA5261

34,33,32

3,5,7

16,13,

1,4,6

1,2 4,5

14,15

18,19,20

SMPS

Controller

STR

F6707

5 3

TROUBLESHOOTING

Check voltage of C806(+)

1. No Power (Not working SMPS)

Check the voltage at

pin4 of IC803

Check / Replace

F801, SW801, T801 & DB801

R811,TH803 (option)

130 ¡- 380V 0V

Check / Replace

T802,D806 & R815

Check / Replace

IC803 and secondary part of power circuit

Check / Replace

R806, IC801 & R804

17¡-19V

2. No Power On (SMPS working)

Check Micom On/Off port

Check / Replace

R817,Q807,

IC802 & IC844

Check / Replace

MICOM

ON OFF

Check / Replace

Q401,T401,R412,

R418 & R405

Check / Replace

IC501

2.0V

Check H-Out voltage at

Pin32 of IC501.

Check / Replace

IC501

Check / Replace

R303,R304 C301,C311

IC301

4.9V

Check the Voltage

at Pin 13 of IC501

3. No Power off (SMPS working )

Check / Replace

Q801,D842&D844

Check +B

at D807 cathode

Check the voltage at (pin3,

17,28,52) of IC501 ?

Check

F801 of AC line

Check the voltage

of C806

Check the voltage

of pin4

Check the voltage at

pin32 of IC501(H-out)

Check Q401

collector waveform

Check T401

& each pin voltage

Check the collector

waveform of Q402

Check & Replace

IC501

Check & Replace

Q401

Check & Replace R405,C408,T401

Check the in/out

of IC844

Check at pin5

of Micom?

Check /Replace

Q807

Check /replace

D806,IC803 , R809 & R811

Check /replace

Fuse,DB801& IC803

Check /replace

TH803(option)

Normal Abnormal

Yes

254~380V

Open

4. No Raster

Check /Replace

C402,C414,Q402

Check the

Heater voltage of CPT

(6 6.5Vrms)

Check

FR401,P902A & P902B

Check

FBT (T402)

Check the

Heater pulse of FBT

T701

OK Not OK

Check/Replace

CPT Board

Components

Check

HV & Screen voltage of

CPT

Check

the voltage

at pin1 of P902A

6. No Raster / Sound OK

180~190V

Check/Replace

FBT (T402)

Check/Replace

Q901,Q902 & Q903

Is any OSD displayed?

Check receiving system in MENU

& excute Auto-program.

Check pin1(H-Sync),

pin2(V-Sync) of IC01

Check IC01 pin19(XLS),

pin20(EXLC) of IC01

Go to NO SOUND / PICTURE OK

Does the Auto-program

operate properly.

Store in manual-program MENU

Check 5V, 33V & IIC Bus Line

of TUNER(TU101)

Is the CVBS signal OK.

( pin47 of IC501)

Check R,G,B signal

at pin18,19,20 of IC501

Check

5V, 33V &

IIC Bus Line

Check / Replace

TUNER, IC501

Check / Replace

CPT Board component

Check

CVBS signal Line

& IC501

Check pin40(B),41(G),42(R)

of IC01

7. No Picture / No Sound

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