LG 42LV5400-UB Service Manual
The LG 42LV5400-UB is a 42-inch LED TV with Full HD 1080p resolution, built-in digital tuner, multiple HDMI inputs, USB connectivity, Smart TV features, energy saving modes, and advanced picture processing. This service manual covers technical specifications, disassembly procedures, troubleshooting, circuit diagrams, and repair guidelines for qualified service technicians.
Product Overview
The LG 42LV5400-UB features LED backlight technology with local dimming, 120Hz refresh rate, and LG's Cinema 3D technology. Key components include main board, power supply board, T-Con board, LCD panel, and LED backlight assembly.
| Component | Part Number |
|---|
| Main Board | EAX64936801 |
| Power Supply Board | EAY62915601 |
| T-Con Board | 6870C-0594A |
| LCD Panel | LC420EUN |
| LED Backlight | LGZ42180101 |
| Remote Control | AKB72915207 |
Technical Specifications
- Screen Size: 42 inches LED
- Resolution: 1920 x 1080 Full HD
- Refresh Rate: 120Hz
- Backlight: Edge LED with local dimming
- Inputs: 4x HDMI, 3x USB, Component, Composite, RF
- Smart TV: NetCast 3.0
- Power Consumption: 85W typical, 0.3W standby
- Power Supply: 100-240V AC, 50/60Hz
- Dimensions: 37.7" x 22.4" x 2.8"
- Weight: 25.4 lbs
Disassembly Instructions
Follow these steps for safe disassembly of the TV unit.
- Remove stand: Lay TV face down on soft surface, remove screws holding stand.
- Remove rear cover: Remove all screws from rear casing, carefully pry open clips.
- Disconnect cables: Note cable positions before disconnecting from main board.
- Remove main board: Unscrew mounting screws, lift board carefully.
- Access power supply: Remove screws and disconnect power cables.
- LCD panel removal: Extreme care required - use suction cups for handling.
WARNING! High voltages present even when unplugged. Discharge capacitors before handling power supply.
Main Board Replacement
Procedure for replacing the main logic board (EAX64936801).
- Disconnect all cables from main board including LVDS, power, and input cables.
- Remove 6 mounting screws securing main board to chassis.
- Carefully lift board from mounting posts.
- Install new main board, ensuring proper alignment with mounting holes.
- Reconnect all cables in original positions.
- Test functionality before reassembling.
Note: Main board contains EEPROM with serial number and calibration data.
Power Supply Board
The power supply board (EAY62915601) provides multiple voltage rails.
| Output | Voltage | Current | Purpose |
|---|
| +12V | 12V DC | 5A | Main board power |
| +24V | 24V DC | 2.5A | LED backlight driver |
| +5V STBY | 5V DC | 1A | Standby power |
| +3.3V | 3.3V DC | 2A | Processor power |
Safety: Always check for short circuits before applying power to repaired boards.
LCD Panel & Backlight
The LC420EUN panel uses edge-lit LED technology with 4 LED strips.
- LED strips are located on top and bottom edges of panel.
- Each strip contains 24 LEDs (48 total).
- LED driver circuit provides constant current to strips.
- Backlight failure symptoms: dark screen, flashing backlight, or no backlight.
- LED testing: Use LED tester or power supply with current limit.
CAUTION! LCD panel is fragile and expensive - handle with extreme care.
Troubleshooting Flowcharts
Systematic approach to common problems.
| Symptom | First Check | Next Steps |
|---|
| No Power | Check AC input, fuse | Test standby voltage, check main board |
| No Backlight | Check 24V supply | Test LED strips, driver circuit |
| No Picture | Check LVDS cable | Test T-Con board, main board outputs |
| No Sound | Check volume settings | Test audio IC, speakers, main board |
| Smart TV Issues | Check network connection | Update firmware, check WiFi module |
Circuit Diagrams
Reference schematics for major circuits.
- Main board power distribution
- LED backlight driver circuit
- Audio amplifier circuit
- T-Con board timing controller
- HDMI input circuits
- Power supply primary and secondary
Note: Complete schematics available in separate PDF files.
Test Points & Voltages
Critical test points for diagnosis.
| Test Point | Normal Voltage | Location |
|---|
| TP201 | 3.3V | Main board near processor |
| TP302 | 1.2V | Main board DDR memory |
| TP401 | 12V | Power supply output |
| TP501 | 24V | LED driver input |
| TP601 | 15V | Audio amplifier |
Firmware Update
Procedure for updating TV firmware.
- Download latest firmware from LG service website.
- Format USB drive to FAT32, extract firmware files to root directory.
- Insert USB drive into TV USB port while TV is off.
- Press and hold POWER button on TV (not remote) until update begins.
- Do not interrupt power during update process (approx. 5-10 minutes).
- TV will restart automatically when update completes.
WARNING! Incorrect firmware or interrupted update can brick the TV.
Safety Precautions
Essential safety guidelines for service technicians.
- Always disconnect AC power before servicing
- Discharge high-voltage capacitors in power supply
- Use insulated tools when working with live circuits
- Wear ESD protection when handling circuit boards
- Work on anti-static mat with proper grounding
- Never bypass fuses or safety components
- Verify repairs with isolation transformer when possible
Service Support: LG Service Center 1-800-243-0000
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