42LV355H-ZA (CHASSIS:LD0AZ) - LG TV Service Manual (repair manual). Page 12

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- Why need Vcom adjustment?

A

The Vcom (Common Voltage) is a Reference Voltage of
Liquid Crystal Driving.
-> Liquid Crystal need for Polarity Change with every frame.

- Adjust sequence

· Press the PIP key of the Adjustment remote control.(This

PIP key is hot key to enter the VCOM adjusting mode.)

(Or After enter Service Mode by pushing “ADJ” key, then
Enter V-Com Adjust mode by pushing “

G

” key at “10. V-

Com”)

· As pushing the right or the left key on the remote control,

and find the V-COM value which is no or minimized the
Flicker. (If there is no flicker at default value, Press the exit
key and finish the VCOM adjustment.)

· Push the “OK” key to store value. Then the message

“Saving OK” is pop.

· Press the exit key to finish VCOM adjustment.

(Visual Adjust and control the Voltage level)

- When pressing IN-STOP key by Service remote control, Red

LED are blinked alternatively. And then automatically turn off.

(Must not AC power OFF during blinking)

Confirm whether is normal or not when between power
board’s ac block and GND is impacted on 1.5 kV(dc) or 2.2
kV(dc) for one second.

• Press “Power on” key of service remote control.

(Baud rate : 115200 bps)

• Connect RS232 Signal Cable to RS-232 Jack.
• Write Serial number by use RS-232.
• Must check the serial number at the Diagnostics of SET UP

menu. (Refer to below.)

CMD

: A0h

LENGTH : 85~94h (1~16 bytes)
ADH

: EEPROM Sub Address high (00~1F)

ADL

: EEPROM Sub Address low (00~FF)

Data

: Write data

CS

: CMD+LENGTH+ADH+ADL+Data_1+…+Data_n

Delay

: 20ms

* Description

FOS Default write : <7mode data> write
Vtotal, V_Frequency, Sync_Polarity, Htotal, Hstart, Vstart, 0,
Phase
Data write: Model name and Serial number write in EEPROM,.

A. Serial number D/L is using of scan equipment.
B. Setting of scan equipment operated by Manufacturing

Technology Group.

C. Serial number D/L must be conformed when it is produced

in production line, because serial number D/L is mandatory
by D-book 4.0.

Row  Li ne

Column  Line

C

LC

C

ST

S

Y

S

T

E

M

Gat

e

 Driv

e

 IC

So urce D r i v e  I C

Ti m i n g  
Co nt r o ll e r

Po w e r  
Blo ck

V

COM

Ga mma
Re f e r e nce V o ltage

Gamm a Reference
Volta ge

Data (R ,G,B ) & C ont ro l s ignal

Con t rol si gnal

Data (R ,G,B ) &
Con t rol si gnal

In
te

rf

a

c

e

TFT

Po w e r  I n p u t

Power Input

Da t a  I n p u t

Da t a  I n p u t

V

COM

Liquid 
Crys tal

V

COM

No.

Adjust mode

CMD(hex)

LENGTH(hex)

Description

1

EEPROM WRITE

A0h

84h+n

n-bytes Write(n=1~16)