LG 55LB5900 Service Manual

The LG 55LB5900 is a 55-inch LED TV featuring Full HD 1080p resolution, built-in digital tuner, multiple HDMI inputs, USB connectivity, Smart TV capabilities, ENERGY STAR certification, and advanced picture processing technologies. This service manual provides comprehensive technical information for qualified service technicians including disassembly procedures, circuit diagrams, troubleshooting guides, and replacement part information.

Safety Precautions

Before servicing, read all safety warnings and precautions. This equipment contains hazardous voltages that can cause electric shock.

Product Specifications

• Model: 55LB5900
• Screen Size: 55 inches LED
• Resolution: Full HD 1920x1080
• TV System: ATSC/NTSC/QAM
• Connectivity: 3x HDMI, 2x USB, Component, Composite, RF
• Smart TV: WebOS 2.0
• Power Supply: 120V AC, 60Hz
• Power Consumption: 85W typical
• Standby Power: < 0.5W

Disassembly Procedures

Follow these steps carefully to disassemble the TV for service.

1. Remove stand: Lay TV face down on soft surface, remove screws securing stand.
2. Remove rear cover: Remove all screws from rear cover, carefully pry open.
3. Disconnect cables: Note cable positions before disconnecting from main board.
4. Remove boards: Remove screws securing power supply, main, and T-con boards.
5. Access panel: Remove metal chassis to access LCD panel and LED strips.

WARNING! Always discharge power supply capacitors before handling internal components.

Main Board Replacement

Main board EAX65419301 controls all TV functions and inputs.

1. Disconnect all cables from main board including power, T-con, and input cables.
2. Remove 6 screws securing main board to chassis.
3. Carefully lift main board out of chassis.
4. Install new main board and secure with screws.
5. Reconnect all cables in original positions.
6. Test all functions before reassembling.

NOTE: Main board contains EEPROM with serial number and calibration data.

Power Supply Board

Power supply board EAY64919401 provides all required voltages.

CAUTION! LED driver voltage is high and can cause severe shock.

LED Backlight System

Direct LED backlight system with 4 LED strips, 24 LEDs per strip.

1. LED strips are connected in series with total forward voltage ~120V.
2. Each LED strip part number: 6871Q-0584A
3. LED driver current: 300mA typical
4. To test individual strips: Measure voltage drop across each LED
5. Replace entire strip if multiple LEDs are failed

WARNING! Do not operate LED backlight without diffuser sheets installed.

T-Con Board

T-Con board processes video signal for LCD panel.

• Part Number: 6870C-0736A
• Input: LVDS from main board
• Output: Panel ribbon cables
• Main IC: TCON TSUMV59XU
• Voltages: +12V, +3.3V, +1.8V

Troubleshooting: Check fuse F1 on T-con board for open circuit.

Panel Components

LCD panel assembly includes glass, polarizers, and driver circuits.

NOTE: LCD panel replacement requires complete disassembly.

Troubleshooting Flowcharts

Systematic approach to common problems.

1. No Power: Check AC input, standby voltage, main board power-on signal
2. No Backlight: Check LED driver voltage, LED strips, backlight enable
3. No Picture: Check T-con voltages, LVDS signal, panel VGH/VGL
4. No Sound: Check audio IC, speakers, audio processing
5. No Tuner: Check tuner power, antenna connection, tuner IC

Test Points & Voltages

Critical test points for voltage measurements.

Parts List & Ordering

Genuine LG replacement parts.

Ordering: Contact LG Parts at 1-800-243-0000 or www.lgpartsonline.com