LG 42LD550 Service Manual

The LG 42LD550 is a 42-inch LCD TV with Full HD 1080p resolution, built-in digital/analog tuner, multiple HDMI inputs, USB connectivity, Intelligent Sensor for automatic picture optimization, Clear Voice II for enhanced dialogue clarity, and energy saving features. Below are key sections for technical specifications, disassembly procedures, circuit diagrams, troubleshooting, and maintenance guidelines.

Product Specifications

Key technical specifications and component details for service and repair purposes.

Disassembly Instructions

Step-by-step procedure for safely disassembling the television unit.

1. Remove stand: Lay TV face down on soft surface, remove screws securing stand.
2. Remove rear cover: Remove all screws from back cover, carefully pry open using plastic tools.
3. Disconnect cables: Note cable positions before disconnecting from main board.
4. Remove shield: Unscrew metal shield covering main components.

WARNING! Always disconnect power before disassembly. Handle LCD panel with care to avoid damage.

Main Board Replacement

Procedure for replacing the main logic board.

1. Disconnect all cables from main board including power, LVDS, and input cables.
2. Remove mounting screws securing main board to chassis.
3. Carefully lift main board out of chassis.
4. Install new main board and reconnect all cables in original positions.

CAUTION! Use anti-static precautions. Ensure all connectors are firmly seated.

Power Supply Unit

• Model: EAX61732402
• Input Voltage: 100-240V AC, 50/60Hz
• Output Voltages: +5VSB, +12V, +24V for backlight
• Test Points: TP1 (+5VSB), TP2 (+12V), TP3 (+24V)
• Protection: Over-voltage, over-current, short-circuit protection
• Replacement: Ensure exact model match for compatibility

T-Con Board Procedures

Timing Control board maintenance and replacement guidelines.

Location: Connected directly to LCD panel via LVDS cables.

Replacement: Disconnect LVDS cables, remove mounting screws, replace with identical model. Calibration: Use service remote for gamma and color calibration adjustments. Testing: Check VGH, VGL, VCOM voltages for proper operation.

LCD Panel Handling

Proper handling procedures for LCD panel replacement and maintenance.

1. Always handle panel by edges; avoid pressure on screen surface.
2. Use clean, lint-free gloves to prevent fingerprints and contamination.
3. Store panel in anti-static bag when not installed.
4. Ensure work area is clean and free of debris.

Tip: Use suction cup tools for safe panel removal and installation.

Backlight System

CCFL backlight system maintenance and replacement procedures.

1. Remove LCD panel to access backlight assembly.
2. Inspect CCFL tubes for dark spots or damage.
3. Test inverter output voltages (typically 600-800V AC).
4. Replace CCFL tubes in sets; never replace single tube.
5. Reassemble in reverse order, ensuring proper alignment.

WARNING! High voltage present. Discharge capacitors before working on inverter board.

Software Update

Firmware update procedures for main board software.

USB Update: Download firmware to USB drive, insert in service USB port, enter service menu to initiate update. Factory Reset: Clears settings and returns to original firmware state. Service Menu: Access with service remote for advanced diagnostics and adjustments.

Test Points & Voltages

Critical test points and expected voltage readings for diagnostics.

Safety Precautions

Essential safety guidelines for service technicians.

Always disconnect AC power before servicing. Use isolated tools for live testing. Discharge large capacitors before handling. Follow electrostatic discharge (ESD) precautions for sensitive components.

CAUTION! High voltage present in power supply and backlight circuits. Use appropriate personal protective equipment.

Troubleshooting Guide

Reset Procedure: Unplug TV, hold power button 30 seconds, reconnect power.

Service Support: LG Service Center 1-800-243-0000; www.lg.com