LG 42LH40 Service Manual

The LG 42LH40 is a 42-inch LCD HDTV featuring Full HD 1080p resolution, built-in digital/analog tuner, multiple HDMI inputs, USB connectivity, Intelligent Sensor technology for automatic picture optimization, 120Hz refresh rate, and various picture enhancement technologies. Below are key sections for technical specifications, disassembly procedures, circuit diagrams, troubleshooting, and service adjustments.

1. Product Overview 2. Technical Specifications 3. Disassembly Procedures 4. Circuit Diagrams 5. PCB Layouts 6. Troubleshooting Guide 7. Service Adjustments 8. Parts List 9. Safety Precautions 10. Block Diagram 11. Firmware Update

Product Overview

Key components: 42-inch LCD panel, main board, power supply board, T-CON board, inverter board, speakers, and remote control.

Component	Description
Main Board	LVDS signal processing and input switching
Power Supply Board	Provides various DC voltages to all circuits
T-CON Board	Timing controller for LCD panel driving
Inverter Board	Backlight CCFL driving circuit
Speakers	10W x 2 stereo audio output
Remote Control	AKB72915207 with learning function

Technical Specifications

Screen Size: 42 inches LCD
Resolution: 1920 x 1080 (Full HD)
TV System: ATSC/NTSC/QAM
Inputs: 4 x HDMI, 2 x Component, 2 x Composite, 1 x PC Input, 1 x USB
Sound Output: 20W (10W x 2)
Refresh Rate: 120Hz
Power Consumption: 180W (typical)
Standby Power: Less than 1W
Operating Voltage: 100-240V AC, 50/60Hz

Disassembly Procedures

Follow these steps carefully for safe disassembly:

Remove stand: Lay TV face down on soft surface, remove screws holding stand.
Remove rear cover: Remove all screws from rear cabinet, carefully separate rear cover.
Disconnect cables: Note cable positions before disconnecting from main board.
Remove boards: Unscrew and remove power supply, main, and T-CON boards as needed.
LCD panel removal: Extreme care required - use suction cups and follow specific procedure.

WARNING! High voltages present even when unplugged. Discharge capacitors before handling.

Circuit Diagrams

Complete schematic diagrams for all major circuits:

Power Supply Circuit (EAX61722601)
Main Board Circuit (EAX61722701)
T-CON Board Circuit (6870C-0594A)
Inverter Board Circuit (6871Q-0354A)
Audio Amplifier Circuit

Note: All diagrams include component values and test points.

PCB Layouts

Physical board layouts with component placement:

Board	Part Number	Description
Main Board	EAX61722701	Main signal processing board
Power Supply	EAX61722601	Switching power supply unit
T-CON Board	6870C-0594A	Timing control board
Inverter Board	6871Q-0354A	Backlight inverter

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
No Power	Power supply failure	Check fuse F101, measure standby voltage (5V STBY)
No Backlight	Inverter failure	Check inverter output, replace CCFLs if needed
No Picture/Sound	Main board failure	Check LVDS output, replace main board
Vertical Lines	T-CON or panel failure	Check T-CON voltages, replace T-CON board
No HDMI Input	HDMI IC failure	Replace HDMI IC or main board

Service Adjustments

Factory service mode adjustments:

Enter Service Mode: Press MENU on remote, then press 1-1-2-5 on TV buttons.
White Balance: Adjust R/G/B gain and offset values.
Picture Settings: Factory default picture mode adjustments.
Option Settings: Regional and feature settings.
Exit Service Mode: Press EXIT to save and exit.

CAUTION! Incorrect adjustments may cause permanent damage.

Parts List

Critical replacement parts:

Main Board: EAX61722701
Power Supply: EAX61722601
T-CON Board: 6870C-0594A
Inverter Board: 6871Q-0354A
LCD Panel: LC420WUN-SAA1
Remote Control: AKB72915207
Backlight CCFL: 42" CCFL tube set

Safety Precautions

Essential safety procedures for service technicians:

Always disconnect AC power before servicing.
Discharge high-voltage capacitors before handling.
Use insulated tools when working with live circuits.
Wear ESD protection when handling circuit boards.
Follow proper LCD panel handling procedures.

WARNING! High voltage present - risk of electric shock.

Block Diagram

System block diagram showing signal flow:

Tuner Section: ATSC/NTSC/QAM signal processing
Video Processing: HDMI, Component, Composite inputs
Audio Processing: Dolby Digital decoding
Power Management: Standby and main power control
Backlight Control: Inverter and dimming circuits

Firmware Update

Firmware update procedure:

Download latest firmware from LG service website.
Copy to USB drive (FAT32 format).
Insert USB into TV USB port.
Enter Service Menu and select USB Update.
Do not power off during update process.

Service Support: LG Service Center 1-800-243-0000