LG 42LN5200-UM Service Manual

The LG 42LN5200-UM is a 42-inch LED TV with Full HD 1080p resolution, built-in digital tuner, multiple HDMI inputs, USB connectivity, ENERGY STAR® compliance, and advanced picture processing technologies. This service manual provides comprehensive technical information for service technicians including disassembly procedures, circuit diagrams, troubleshooting guides, and replacement parts information.

Product Overview

Key components: LED panel, main board, power supply board, T-CON board, LED backlight assembly, and various input/output connectors.

Technical Specifications

• Screen Size: 42 inches LED
• Resolution: 1920 x 1080 Full HD
• TV System: ATSC/NTSC/Clear QAM
• Connectivity: 3 x HDMI, 2 x USB, Component, Composite, RF Input
• Sound Output: 20W (10W x 2)
• Power Consumption: 65W (typical), <0.5W (standby)
• Power Supply: 100-240V AC, 50/60Hz
• Operating Temperature: 0°C to 40°C
• Dimensions: 37.7" x 22.4" x 3.2" (with stand)
• Weight: 22.5 lbs (with stand)

Disassembly Procedures

Complete step-by-step disassembly instructions for service access.

1. Rear Cover Removal: Remove all screws from rear cover, carefully separate cover from chassis.
2. Stand Removal: Remove screws securing stand to main chassis.
3. Main Board Access: Disconnect all cables, remove mounting screws, lift board out.
4. Power Board Removal: Disconnect AC input and output cables, remove mounting screws.
5. Panel Disassembly: Remove bezel screws, carefully separate front bezel from panel assembly.
6. LED Strip Replacement: Remove diffuser sheets, access LED strips for replacement.

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

Circuit Diagrams

Detailed circuit schematics for all major boards and subsystems.

• Main Board Schematic: Complete circuit diagram with IC pinouts
• Power Supply Schematic: AC/DC conversion and voltage regulation circuits
• T-CON Board Schematic: Timing control and LVDS interface circuits
• LED Driver Schematic: Backlight driving and dimming control
• Input/Output Circuits: HDMI, USB, and audio/video input circuits

Note: All schematics include voltage test points and component values.

Main Board Replacement

Procedure for replacing the main board (EBT63912401).

1. Disconnect all cables from main board including power, panel cables, and input/output connectors.
2. Remove all mounting screws securing main board to chassis.
3. Carefully lift main board out of chassis, avoiding damage to connectors.
4. Install new main board, ensuring proper alignment with mounting holes.
5. Reinstall all mounting screws and reconnect all cables.
6. Power on and verify proper operation.

CAUTION! Ensure proper ESD protection during board handling.

Power Supply Board

Troubleshooting and repair procedures for power supply board (EAY62918401).

Safety: Always verify capacitors are discharged before testing.

LED Backlight System

Diagnosis and repair of LED backlight system.

1. Backlight Test: Shine flashlight on screen to check for image with no backlight.
2. LED Strips: 6 LED strips with 12 LEDs per strip, series connected.
3. Driver Circuit: Check LED driver output voltage and current.
4. Replacement: Replace individual LED strips or complete backlight assembly.
5. Calibration: Adjust backlight current for uniform brightness.

WARNING! High voltage present on LED driver output.

Troubleshooting Flowcharts

Step-by-step diagnostic procedures for common issues.

• No Power Flowchart: AC input → fuse → rectifier → standby circuit → main power
• No Picture Flowchart: Backlight check → T-CON voltages → main board output
• No Sound Flowchart: Audio input → audio processor → amplifier → speakers
• HDMI Issues: Source check → cable test → HDMI input circuit → main processor
• Remote Control Issues: Battery check → IR sensor → key board → main board

Error Codes

Diagnostic error codes and their meanings.

Firmware Update

Procedures for updating TV firmware.

1. Download latest firmware from LG service website.
2. Format USB drive to FAT32 and copy firmware file.
3. Insert USB drive into TV USB port.
4. Enter service menu and select firmware update.
5. Do not power off during update process.
6. TV will restart automatically after update completion.

CAUTION! Incorrect firmware can permanently damage TV.

Parts List

Replacement parts and their part numbers.