LG 42LD490 Service Manual

The LG 42LD490 is a 42-inch LCD television featuring Full HD 1080p resolution, built-in digital and analog tuners, multiple HDMI inputs, USB connectivity, energy saving technology, and advanced picture processing. This service manual provides comprehensive technical information for service technicians including disassembly procedures, circuit diagrams, troubleshooting guides, and replacement part information.

1. Product Overview 2. Technical Specifications 3. Disassembly Instructions 4. Circuit Diagrams 5. PCB Layouts 6. Troubleshooting Procedures 7. Replacement Parts List 8. Adjustment Procedures 9. Safety Precautions 10. Block Diagrams 11. Test Points & Voltages

Product Overview

The LG 42LD490 features a 42-inch LCD panel with 1920x1080 resolution, 60Hz refresh rate, and 5000:1 dynamic contrast ratio. Key components include main board, power supply board, T-con board, LCD panel, and backlight system.

ComponentDescription
Main BoardEAX61743001 - Main processing unit with HDMI, USB, and tuner inputs
Power SupplyEAY62833701 - Provides various DC voltages to all boards
T-Con BoardEAX61743402 - Timing controller for LCD panel driving
LCD PanelLC420EUN - 42-inch LCD panel assembly
BacklightCCFL backlight system with inverter board
Remote ControlAKB72915207 - Standard infrared remote control
Speakers2x 10W stereo speakers
Inputs/Outputs3x HDMI, 2x USB, Component, Composite, RF, PC input

Technical Specifications

Disassembly Instructions

Follow these steps carefully for safe disassembly of the television.

  1. Remove Stand: Lay TV face down on soft surface, remove 4 screws securing stand.
  2. Remove Rear Cover: Remove all screws from rear cover, carefully separate cover from chassis.
  3. Disconnect Cables: Note cable positions before disconnecting from main board.
  4. Remove Main Board: Remove mounting screws and carefully lift board from chassis.
  5. Access Power Supply: Remove screws and disconnect all power connectors.
  6. LCD Panel Removal: Remove bezel screws, carefully separate LCD assembly from frame.

WARNING! Always discharge power supply capacitors before working on power board. Handle LCD panel with extreme care to avoid damage.

Circuit Diagrams

Complete circuit schematics for all major boards including power supply, main board, and T-con board.

DiagramDescriptionReference
Power SupplyEAY62833701 complete schematicPage 25-28
Main BoardEAX61743001 full circuit diagramPage 29-45
T-Con BoardEAX61743402 timing controllerPage 46-52
Inverter BoardBacklight inverter circuitPage 53-55
Audio BoardAmplifier and audio processingPage 56-58

Note: All diagrams include component values and test point locations.

PCB Layouts

Detailed printed circuit board layouts showing component placement and routing.

  1. Main Board Top Side: Component placement and identification
  2. Main Board Bottom Side: SMD components and solder points
  3. Power Supply Board: High voltage section isolation
  4. T-Con Board: LVDS connector and timing components
  5. Inverter Board: Transformer locations and output connectors

CAUTION! Observe ESD precautions when handling PCBs. Use proper grounding equipment.

Troubleshooting Procedures

Systematic troubleshooting guide for common failure symptoms.

SymptomPossible CauseCorrective Action
No PowerPower supply failure, main board issueCheck fuse F101, measure standby voltage, test power IC U201
No BacklightInverter failure, backlight tubesCheck inverter output, test backlight tubes, replace inverter board
No PictureT-con board, LVDS cable, main boardCheck LVDS voltages, test T-con board, replace main board
No SoundAudio IC, speaker connectionsTest audio IC U601, check speaker impedance, replace audio board
HDMI Not WorkingHDMI port, main board ICCheck HDMI IC U301, test port connections, replace main board
USB Not RecognizedUSB port, main board ICTest USB IC U401, check port connections, update firmware

Replacement Parts List

Complete list of replacement parts with manufacturer part numbers.

Part NumberDescriptionQty
EAX61743001Main Board Assembly1
EAY62833701Power Supply Board1
EAX61743402T-Con Board1
LC420EUN-SEF1LCD Panel Assembly1
6871Q-0148AInverter Board1
AKB72915207Remote Control1
10-BS101-01SPower Button1
F101Fuse 4A/250V1

Note: Always verify part numbers before ordering replacements.

Adjustment Procedures

Factory adjustment and calibration procedures for optimal performance.

  1. White Balance Adjustment: Enter service menu, adjust RGB gains and offsets
  2. Backlight Adjustment: Set backlight level to factory specification
  3. Color Temperature: Calibrate warm, normal, and cool settings
  4. Geometry Adjustment: Adjust horizontal/vertical position and size
  5. Sound Adjustment: Set audio levels and equalizer settings
  6. Tuner Alignment: Fine-tune digital and analog tuner reception

WARNING! Service menu adjustments should only be performed by qualified technicians.

Safety Precautions

Critical safety information for service personnel.

DANGER! High voltages present in power supply and inverter circuits can cause serious injury or death.

Block Diagrams

System block diagrams showing signal flow and interconnections.

DiagramDescription
System OverviewComplete signal flow from inputs to display
Power DistributionDC voltage distribution to all subsystems
Video ProcessingVideo signal processing path
Audio ProcessingAudio signal processing and amplification
Control SystemMicrocontroller and interface control

Refer to pages 59-68 for detailed block diagrams with component references.

Test Points & Voltages

Critical test points and expected voltage readings for troubleshooting.

Test PointLocationNormal VoltageDescription
TP201Power Board5V STBYStandby voltage
TP202Power Board12VMain 12V supply
TP203Power Board24VBacklight supply
TP301Main Board3.3VDigital logic supply
TP302Main Board1.8VCore voltage
TP401T-Con Board12VPanel supply
TP402T-Con Board3.3VLogic supply
TP501Inverter Board800V ACBacklight output

Service Support: LG Service Center 1-800-243-0000 | www.lgservice.com

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