DOWNLOAD LG 42LH20FD (CHASSIS:LT91A) Service Manual ↓ Size: 4.29 MB | Pages: 75 in PDF or view online for FREE

THE    SYMBOL MARK OF THIS SCHEMETIC DIAGRAM INCORPORATES
SPECIAL FEATURES IMPORTANT FOR PROTECTION FROM X-RADIATION.
FILRE AND ELECTRICAL SHOCK HAZARDS, WHEN SERVICING IF IS 
ESSENTIAL THAT ONLY MANUFATURES SPECFIED PARTS BE USED FOR
THE CRITICAL COMPONENTS IN THE    SYMBOL MARK OF THE SCHEMETIC.

0

32"UP_IR_KEY

R980

BLM18PG121SN1D

L957

AMOTECH

5.6V

D956

12507WS-12L

EAG58732902

32"UP_IR_KEY

P953

1

SCL

2

SDA

3

GND

4

KEY1

5

KEY2

6

5V_ST

7

GND

8

WARM_ST

9

IR

10

GND

11

3.3V

12

PWR_ON

13

BLM18PG121SN1D

32"UP_IR_KEY

L953

5.6V

26"UNDER_IR

D952

0 . 1 u F

32"UP_IR_KEY

C976

0 . 1 u F

32"UP_IR_KEY

C971

26"UNDER_KEY

L952

26"UNDER_IR

L956

AMOTECH

5.6V

26"UNDER_KEY

D954

5.6V

26"UNDER_IR

D951

26"UNDER_IR

L955

0 . 1 u F

16V

C975

IR

KEY2

0 . 1 u F

16V

32"UP_IR_KEY

C980

AMOTECH

5.6V

32"UP_IR_KEY

D955

AMOTECH

5.6V

32"UP_IR_KEY

D958

26"UNDER_KEY

L954

32"UP_IR_KEY

L951

5.6V

D959

0

R978

32"UP_IR_KEY

1000pF

50V

C978

4.7K

R973

+3.3V_ST

100

R972

KEY1

0 . 1 u F
16V

26"UNDER_KEY

C972

0

OPT

R979

1000pF

50V

32"UP_IR_KEY

C981

1000pF

26"UNDER_IR

C973

AMOTECH

5.6V

26"UNDER_KEY

D953

SUB/AMP_SDA

SUB/AMP_SCL

4.7K

R974

BLM18PG121SN1D

32"UP_IR_KEY

L958

5.6V

D957

100pF

50V

C979

+5V_ST

POWER_ON/RL_ON

0 . 1 u F
16V

26"UNDER_KEY

C977

100

R971

1000pF

26"UNDER_IR

C974

BLM18PG121SN1D

L959

+3.3V

12507WS-08L

EAG58732904

26"UNDER_IR

P951

1

KEY1

2

KEY2

3

GND

4

5V_ST

5

GND

6

IR

7

LED_B

8

LED_R

9

.

2SC3052

OPT

Q910

E

B

C

47K

OPT

R985

2SC3052

OPT

Q911

E

B

C

10K

OPT

R983

22

OPT

R981

+5V_ST

47K

OPT

R982

+5V_ST

IR_OUT

47K

OPT

R984

0 . 1 u F

16V

C982

32"UP_IR_KEY

10K

R986

32"UP_IR_KEY

12507WR-03L

26"UNDER_KEY

P952

1

KEY1

2

KEY2

3

GND

4

0

OPT

R920

LED_G_SUB

LED_ON/LED_R

LED_G

LED_ON/LED_R

MDS61887701

SMD GASKET-LVDS

M1

MDS61887701

SMD GASKET-MEMORY1

M2

MDS61887701 SMD GASKET-MEMORY2

M3

100

R975

32"UP_IR_KEY

100

R976

32"UP_IR_KEY

IR

11

10

CONTROL & IR & LED

EAX60838501_MERCURY

Taiwan_LH20/LH30

EAX60838501

      2 0 0 9 . 0 2 . 1 0

LGE Use Only

No.

Error symptom (High category)

Error symptom (Mid category)

Page

Remarks

1

A. Video error

No video/Normal audio 

1

2 

No video/No audio

2

3

Video error, video lag/stop

3

4

Color error

4

5

Vertical/Horizontal bar, residual image, 
light spot, external device color error

5

6

B. Power error

No power

6

7

Off when on, off while viewing, power auto 
on/off

7

8

C. Audio error

No audio/Normal video  

8

9

Wrecked audio/discontinuation/noise

9

10

D. Function error

No response in remote controller, key error, 
recording error, memory error

10

11

External device recognition error 

11

12

E. Noise

Circuit noise, mechanical noise

12

13

F. Exterior error

Exterior defect

13

First of all, Check whether there is SVC Bulletin in GCSC System for these model.

Normal 

audio

Y

N

Move to No 
video/No audio

No video
Normal audio

Check Back Light
On with naked eye

On

Y

N

Check Power 
Board
12v,5v  etc.

Normal 

voltage

Y

N

Replace Main Board

Replace T-con 
Board or module
And Adjust VCOM

OR

Repair Power 
Board or parts

Check Power Board 20V /12V or 24v output

Normal
voltage

Y

Replace Inverter 
or module

N

Repair Power 
Board or parts

End

Always check & record S/W Version and White 
Balance value before replacing the Main Board

Replace Main Board 

Re-enter White Balance value

※Precaution

(Main B/D↔ Power B/D, LVDS Cable,Speaker Cable,IR B/D Cable,,,)

1