LG 47LG90 LED LCD TV - MAIN BOARD REMOVAL - SERVICE MODE
- Remove the two screws holding the Decorative plastic piece on the right side. Remove the plastic piece.
- Remove the three pieces of tape on the left and topside that are shielding the cables as shown.
- Remove the remaining 10 screws indicated by the arrows.
- It is possible that your unit may have the Chocolate (Heat Transfer) material over the two large ICs. (See white squares) Maybe even behind the ICs. If so, pay attention to the location and return when reassembling.
- Warning: The Tape shown Is Conductive. Do not allow touching electrically charged components.
- Disconnect P1000, P1001, P800, P404 and P501.
- Note: In the top right is a connector P200. This is an open connection.
- Remove the 2 screws securing the Main PWB.
- Note: The top 2 and bottom 2 screws were removed during the shield removal process.
- NOTE: Look carefully on top and behind the BCM and Micronas Chip, look for a piece of Chocolate (Heat Transfer Material). Be sure to transfer to new PWB if replaced.
- Turn the Set On
- Simultaneously, Press and “Hold” the Menu Key on the Side Key pad and Press and “Hold” the Menu Key on the Remote approximately 5 seconds.
- If Customer’s Menu appears, continue to hold until it disappears.
- The Service Menu appears.
Note: It is possible, dependant upon the
Software Version, a Password may be required to enter the Service Menu. If a
password is required, enter 0000.
- Look at the symptom carefully and determine what circuits could be causing the failure. Use your senses Sight, Smell, Touch and Hearing. Look for burned parts and check for possible overheated components. Capacitors will sometimes leak dielectric material and give off a distinct odor. Frequency of power supplies will change with the load. Observation of the front Power LED may give some clues.
- After carefully checking the symptom and determining the circuits to be checked and after giving a thorough examination using your senses the first check should always be the DC Supply Voltages to those circuits under test. Always confirm the supplies are not only the proper level but be sure they are noise free. If the supplies are missing check the resistance for possible short circuits.
- To further isolate the failure, check for the proper waveforms with the Oscilloscope to make a final determination of the failure. Look for correct Amplitude Phasing and Timing of the signals also check for the proper Duty Cycle of the signals. Sometimes “glitches” or “road bumps” will be an indication of an imminent failure.
- The final step is to correct the problem. Be careful of ESD and make sure to check the DC Supplies for proper levels. Make all necessary adjustments and lastly always perform a Safety AC Leakage Test.
- Check the appearance of the Replacement Panel and Circuit Boards for both physical damage and part number accuracy.
- Check the model label. Verify model names and board model matches.
- Check details of defective condition and history. Example: Oscillator failure dead set, etc…
- Approximately 20 minute pre-run time is required before any adjustments are performed.
- Refer to the Voltage Sticker on the Switch Mode Power Supply silk screening. (+/- ½ volt). .
- Be cautious of electric shock from the Backlight section, it uses high voltage AC. Check that the Power Supply and Drive Circuits are completely discharged because of residual current stored before Circuit Board removal.
- C-MOS circuits are sensitive to static electricity. Use caution when dealing with these IC and circuits.
- Exercise care when making voltage and waveform checks to prevent costly short circuits from damaging the unit.
- Be cautious of lost screws and other metal objects to prevent a possible short in the circuitry.
