LG 42LH20 Service Manual

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Owner's manual (194 pages)

Manual de usuario (124 pages)

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Summary of Contents for LG 42LH20

Page 1 42LH20 42LH20 Direct View LCD Original: March 2009 Updated: February 11, 2010...
Page 2 LCD Overview, General Troubleshooting Steps, Signal Distribution, Disassembly Instructions and Voltages Section 2 Circuit Board Operation, Troubleshooting of : • Switch mode Power Supply • Main Board • T-CON Board • Ft Control Board • Side Keys February 2009 42LH20...
Page 3: Overview Of Topics To Be Discussed
Overview of Topics to be Discussed Overview of Topics to be Discussed 42LH20 LCD Direct View Display Section 1 This Section will cover Contact Information and remind the Technician of Important Safety Precautions for the Customers Safety as well as the Technician and the Equipment.
Page 4: Important Safety Notice
When servicing this product, under no circumstances should the original design be modified or altered without permission from LG Electronics. Unauthorized modifications will not only void the warranty, but may lead to property damage or user injury.
Page 5: Esd Notice
Increase the separation between the equipment and the receiver; Connect the equipment to an outlet on a different circuit than that to which the receiver is connected; or consult the dealer or an experienced radio/TV technician for help. February 2009 42LH20...
Page 6: Contact Information
LG Web Training lge.webex.com LG CS Academy lgcsacademy.com http://136.166.4.200 LCD-DV: 32LG40, 32LH30, 37LH55, 42LG60, 42LG70, 42LH20, 42LH40, 42LH50, 42LH90, 42SL80, 47LG90, 47LH85 PLASMA: 42PG20, 42PQ20, 42PQ30, 50PG20, 50PS80, 50PS60, 60PS11 Plasma Panel Also available on the Also available on the...
Page 7 1. Check the appearance of the Replacement Panel and Circuit Boards for both physical damage and part number accuracy. 2. Check the model label. Verify model names and board model matches. 3. Check details of defective condition and history. Example: Oscillator failure dead set, etc… February 2009 42LH20...
Page 8: Basic Troubleshooting Steps
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 before returning the product back to the Customer. February 2009 42LH20...
Page 9: 42Lh20 Product Information
42LH20 Product Information 42LH20 Product Information This section of the manual will discuss the specifications of the 42LH20 LCD Direct View Display Panel. February 2009 42LH20...
Page 10: Key Features
Two (2) HDMI(TM) (V.1.3 with Deep Color) • ISFccc Ready • Smart Energy Saving • LG SimpLink (TM) (32-inch and above) • LG Core Technologies (32-inch and above) • Dynamic Contrast Ratio 12,000:1 • Response Time (G to G) 8ms •...
Page 11 1365 (H) × 768 (V) Possible Frame Interlaced Rates: 2 Fields to make a Frame 24FPS 1080P Panel 1920 (H) x 1080 (V) 30FPS Progressive 60FPS Each Field is a Frame Think of sync as the Panels “Refresh Rate” February 2009 42LH20...
Page 12 Basic Specifications (LOGO Familiarization) Page 1 Basic Specifications (LOGO Familiarization) Page 1 SIMPLINK Allows for convenient control of other LG SimpLink products using the existing HDMI connection. Clear Voice Technology Automatically enhances and amplifies the sound of the human voice frequency range to provide high-quality dialogue when background noise swells.
Page 13: Remote Control Familiarization
Remote Control Familiarization Remote Control Familiarization BOTTOM PORTION TOP PORTION LCD or PLASMA 2009 Model...
Page 14 Accessing the Service Menu Accessing the Service Menu SIDE KEYS REMOTE To access the Service Menu. TOP PORTION 1) Turn the Set On 2) 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.
Page 15 Rear and Side Input Jacks Rear and Side Input Jacks Rear Input Jacks USB Port Main PWB For Software Upgrades Only Orientation February 2009 42LH20...
Page 16 7) Do not unplug until unit has automatically Do not remove AC power or the USB Flash Drive. restarted. Do not turn off Power, during the upgrade 8) When download is completed, you will see process. “COMPLETE”. 9) Your TV will be restarted automatically. February 2009 42LH20...
Page 17 42LH20 Product Dimensions 42LH20 Product Dimensions 42LH20 Dimensions There must be at least 4 inches of Clearance on all sides 40-3/8" 3-3/8" 1028mm 87.8mm 16-1/8" 8-3/8" 410mm 223mm 7-7/8" 200mm Model No. 7-7/8" 3-9/16" Serial No. 25-11/16" 200mm 90mm Label...
Page 18: Disassembly And Troubleshooting Section
Disassembly: This section of the manual will discuss Disassembly, Layout and Circuit Board Identification, of the 42LH20 LCD Direct View Television. Upon completion of this section the Technician will have a better understanding of the disassembly procedures, the layout of the printed circuit boards and be able to identify each board.
Page 19 Reinsert the stand and stand the unit upright for service position to continue removing the back cover. Remove the Stand by Pulling it out of its Retaining bracket. Remove Remove the one screw hidden by the stand. February 2009 42LH20...
Page 20 Remove the 22 screws indicated. Pay attention to the size and type of screw as there are many different types. Putting in the improper screw when reassembling may Cause damage. Remove the one screw hidden under the stand. See previous page. February 2009 42LH20...
Page 21: Circuit Board Layout
Circuit Board Layout Circuit Board Layout T-CON Under Shield T-CON p/n: EAT60663801 POWER SUPPLY LVDS Cable (Includes Ballast) Side Key with Main PWB Power Button Backlight Backlight Connection Connection To Left Side To Right Side Input Rear Input Inputs Speaker R Power Switch Speaker L Ft IR/LED Control...
Page 22 Power Supply PWB Removal Power Supply PWB Removal P201 Disconnect P201, AC In and SK102, P401 and P402. Remove the 6 screws indicated by the arrows. P402 P401 February 2009 42LH20...
Page 23 Power Supply (Main Power Switch Type 1) Location Power Supply (Main Power Switch Type 1) Location There are three types of Main Power switch used in LG televisions. Type 1: Shuts off AC to the Power Supply. Type 2: Opens ground to the front IR board. (Stand-By 5V Remains, the Main board stays alive).
Page 24 To Main P201 Pin 1 Pin 2 F501 3.15A/250V Run 380V STBY 168V From Hot Gnd F100 6.3A/250V To Backlights AC IN Left Side P402 Master Power Switch SK102 To Backlights AC IN Right Side P401 SK101 February 2009 42LH20...
Page 25 42LH20 Power Supply Turn On Sequence 42LH20 Power Supply Turn On Sequence Ballast Section Primary side fuse: AC In Of the Power Supply Stand-By 168V Run 380V 135V B+ for the 135V No AC Regulator Ballast Bridge Det in Inverter On...
Page 26 42LH20 P700 Main Board to Power Supply P201 Turn On Circuit 42LH20 P700 Main Board to Power Supply P201 Turn On Circuit L708 STBY5V Q706 L728 R739 47KΩ R253 LVDS 12V Panel Power Q704 Q705 10KΩ 0.6V R740 47KΩ L715...
Page 27 ON command (2.8V) to the Power Supply. Check P201 for 24V (Pins 17 or 18) and 12V (Pins 13 or 14). Confirm Pin 20 of P201 went to 3.3V. This is the INV ON signal needed to light the Lamps. Problems with either voltage can be easily solved by following the simple steps on the next page. February 2009 42LH20...
Page 28 (PWR). Apply AC. This will turn on the power supply. Check that the 24V and 12V power supplies are • turned on, P201 (24V pins 17 and 18) (12V pins 13 and 14) (2) Remove AC power. Use P700 Side to insert resistors February 2009 42LH20...
Page 29 (Warning: Disconnect the AC Power first). These pins carry 1.2Kv when active. c) Confirm the INV On/Off line Pin 12 is going to at least 3V. d) If no backlight activity, SMPS is defective. Use P700 Side to insert resistors February 2009 42LH20...
Page 30: Power Supply Connector P201 Voltage And Diode Check
ADIM Pin 21 Fixed and not used PDIM Pin 24 can vary according to type of signal being processed and the OSD Backlight setting. 0.6V 0% to 3.3V 100%. Output from the BCM chip. Diode Mode values taken with all Connectors Removed February 2009 42LH20...
Page 31 2 in STBY and RUN with one lead on Neutral of SK101. With the Master Power Switch Bottom Right of SMPS Closed (On) AC flows. When Open (Off) AC open and does not flow. Neutral Live SK102 SK101 February 2009 42LH20...
Page 32: General Backlight Information
General Backlight Information General Backlight Information To Backlights Over 1.2KV Ballast Section of SMPS To Backlights Over 1.2KV Currently, number of lamps “Unknown” EEFL (External Electrode Fluorescent Lamp) LOW COST Large number of lamps driven by a single inverter February 2009 42LH20...
Page 33 EEFL Compared to CCFL EEFL Compared to CCFL Simple structure, Low price Simple structure Low Cost Complicated structure Lamp manufacturing process Large number of Lamp Lamp assembly structure Drive by single inverter February 2009 42LH20...
Page 34 EEFL Bulb Design Compared to CCFL Key: Long Life Time • For CCFL, Hg gas is consumed mainly near the internal electrode • For EEFL, longer life time is expected because there is no internal electrode consuming Hg gas February 2009 42LH20...
Page 35 Ballast PWB Layout Ballast PWB Layout Viewed from rear SMPS PWB Backlights Test Point Bottom of R406 or R403 38V P/P To Backlights T703 Left Side 1.2Kv To Backlights Right Side T704 February 2009 42LH20...
Page 36 42LH20 P700 Main Board to Power Supply P201 Ballast Turn On Circuit 42LH20 P700 Main Board to Power Supply P201 Ballast Turn On Circuit MAIN PWB POWER SUPPLY BALLAST P201 P700 R717 IC100 SECTION 3.3KΩ +5V General Stand By 5V...
Page 37 Power Supply Backlight Drive Signal Effects Power Supply Backlight Drive Signal Effects Waveform taken using loose coupling. Clip the probe to one of the Backlight wires. Use caution, there is 1.2Kv in the wire. Slow scope setting to 2.4mSec to see the effects of PWM on the waveform.
Page 38: T - Con Board Section
(17V developed at the cathode of D14) and (3.3V developed at the cathode of D13). The 3.3V can also be measured at the ribbon connectors delivering signals to the TFT panel (CN3 pins 57, 58 or 59) and (CN4 pins 2, 3 or 4). February 2009 42LH20...
Page 39: T - Con (Tft Drive) Board Removal
They would have been removed when removing the shield. Remove the 3 Screws in the T-CON shield Be sure to reinstall them if and remove the shield servicing the T-CON PWB. Disconnect CN3, CN4 and CN5. See next slide for details. February 2009 42LH20...
Page 40 Then the flex cable can be easily removed. Press in on the two tabs and slowly rock Unlocked the cable out of the connector. (Shown by the arrows in Fig 3) Fig 2 The locking tab is flipped upward February 2009 42LH20...
Page 41: T - Con Board (With Shield)
CON Board (With Shield) CON Board (With Shield) LVDS (Video and 12V) from Main PWB February 2009 42LH20...
Page 42: T - Con (Tft Drive) Pwb (Shield Removed)
CON (TFT Drive) PWB (Shield Removed) CON (TFT Drive) PWB (Shield Removed) To TFT Panel To TFT Panel T-CON p/n: EAT60663801 FL114 LED1 Remember to replace screws for Main PWB ground purposes if testing the PWB. February 2009 42LH20...
Page 43: T - Con (Tft Drive) Pwb Checks
Anode 3.3V Anode 3.3V Cathode 0V Cathode 0V Cathode 1.3V LED OFF LED ON LED OFF T-CON Check the Regulator U10 for Correct Voltage 3.3V 1.8V Check Fuse F1 for 12V From Pins 2, 3, 4 and 5. February 2009 42LH20...
Page 44: T - Con (Tft Drive) Voltages For The Panel Checks
CON (TFT Drive) Voltages for the Panel Checks CON (TFT Drive) Voltages for the Panel Checks U7B+ 3.3V VGH_M Pin 8 February 2009 42LH20...
Page 45: T - Con (Tft Driver) Board Cn3 And Cn4 (3.3V Voltage Check)
CON (TFT Driver) Board CN3 and CN4 (3.3V Voltage Check) 3.3V Check 3.3V Check If the 3.3Volts is missing, check the 3.3V DC to DC converter. Check at D13 cathode. See previous page for location. T-CON PWB February 2009 42LH20...
Page 46: T - Con Pwb Connector Cn5 To Main Pwb Voltage And Diode Check
Customer’s Menu Backlight setting. But is Not Used by T-CON. NOTE: The outside pins on each side are actually not counted, they are both ground. But they are counted in the table. (See arrow on the T-CON PWB CN5) February 2009 42LH20...
Page 47: Main Board Section
•10 Bit LVDS (10 Pin) to the T-CON Board • Audio output signals to the Speakers • Digital Audio Output Coaxial and Optical • ON OFF Controls to the SMPS turning on low voltage generation and Backlights • Backlight intensity control signal (Digital Dimming) P-DIM February 2009 42LH20...
Page 48 11 screws indicated by the arrows. NOTE: Be sure to check on top and behind the Video Processor IC. Look for a piece of Chocolate (Heat Transfer Material). Be sure to transfer to P1204 new PWB if present. February 2009 42LH20...
Page 49 Be sure to transfer to new PWB if replaced. To SMPS P700 LD1000 SW100 Tuner OK Reset when IC100 X105 LD1000 Green Microprocessor Video Processor X100 Tuner TU1001 Software Upgrade via Jig To Front PWB To Speakers P600 P1204 Assembly February 2009 42LH20...
Page 50: Back View
Main PWB Main PWB Voltages given on the 11X17 foldout “Interconnect Diagram” (Back View) (Back View) IC1003 IC1002 IC102 IC601 IC702 Tuner IC501 IC501 IC500 February 2009 42LH20...
Page 51 42LH20 Main Board (Front View) Component Layout 42LH20 Main Board (Front View) Component Layout IC704 IC705 Q706 IC704 P801 IC105 3.3V_FE 1.26V_VDDC IC1003 Q706 Switch 1 (5V) 3.3V-FE HDCP EEPROM 2 (0.48V) 1 (0.78V) To T-CON (12V LVDS) L726 3 (0.48V)
Page 52 Main PWB X100 and X1005 Check Main PWB X100 and X1005 Check IC100 Microprocessor Crystal 2.28Vp/p 4.95Vp/p 12Mhz 25Mhz X100 Set on or off Only when set is on X400 X1005 Location X100 Location X1005 Tuner Control IC1004 Crystal MAIN PWB February 2009 42LH20...
Page 53 LD1000 Use LD1000 as a visual aid. This lets you know if the tuner internal PLL (Phase Locked Loop) system is locked. Illuminated PLL is normal. Off is abnormal tuner lock. Main PWB LD1000 Location MAIN PWB February 2009 42LH20...
Page 54 Main PWB Tuner with Shield Off (Pin ID) Main PWB Tuner with Shield Off (Pin ID) February 2009 42LH20...
Page 55 Channel. Pin 19 MAIN PWB “Video” Tuner Location Signal 2.24Vp/p Pin 16 “SIF” Pin 1 Signal Pin 12 and Pin 13 “Dig IF” Signal 450mVp/p Note: “Dig IF” Signal only when 700mVp/p receiving a Digital Channel. February 2009 42LH20...
Page 56: Main Pwb Tuner Clock And Data Lines
Main PWB Tuner Clock and Data Lines Main PWB Tuner Clock and Data Lines Note: Pin 9 SCL SCL and SDA only active during an actual Channel Change. 1V per/div 100uS 5V p/p Pin 8 SDA 1V per/div 100uS 5V p/p February 2009 42LH20...
Page 57: Main Pwb Lvds P801 Video Output Check
Pin 1 Pin 6 Pin 30, 29, 28, 27 (LVDS 12V) 500nS P801 Location MAIN PWB Pin 18 This is just a sample of two pins on the LVDS. 500nS There are 8 pins on P801 carrying video. February 2009 42LH20...
Page 58 Main PWB LVDS Connector P801 Pin Identification Main PWB LVDS Connector P801 Pin Identification P801 PWM Dim Screen Video Not used on Video 12V for Size Clock T-CON T-CON Video Video Video February 2009 42LH20...
Page 59 Main PWB Connector P801 to T CON Voltage and Diode Check Main PWB Connector P801 to T CON Voltage and Diode Check Diode Mode values taken with all Connectors Removed P801 CONNECTOR "Main" to CN5 "T-CON PWB" Diode LABEL Diode Check LABEL Check TXA1-...
Page 60 Main PWB Connector P700 to Power Supply Voltage and Diode Check Main PWB Connector P700 to Power Supply Voltage and Diode Check P700 “Main PWB" to P201 “SMPS PWB" Odd Pins Even Pins Diode Diode Label STBY Label STBY Check Check PWR-ON 4.98V...
Page 61 Main PWB Connector P1204 to (Ft. IR/LED Control) Voltage and D iode Check Main PWB Connector P1204 to (Ft. IR/LED Control) Voltage and D iode Check P1204 CONNECTOR "MAIN PWB" to P1 "Front IR / LED PWB Assy" Label STBY Diode Check 3.3V 3.3V...
Page 62: Main Pwb Connector P600 To Speakers Voltage And Diode Check
Main PWB Connector P600 to Speakers Voltage and Diode Check Main PWB Connector P600 to Speakers Voltage and Diode Check P600 CONNECTOR "Main" to "Speakers" LABEL Diode Check SPK-R(-) 10.7V 1.5V SPK-R(+) 10.7V 1.5V SPK-L(-) 10.7V 1.5V SPK-L(+) 10.7V 1.5V Use speaker out to test for defective Audio Amp IC600 Diode Mode values taken with all Connectors Removed LCD or PLASMA 2009...
Page 63: Front Ir Board
FRONT IR BOARD Front (IR and LED Control) Assembly Layout (Back View) The IR Sensor and Power LED control IC are located on the front of this Board To Side Key PWB To Main PWB Cover Cover Removed LCD March 2009 42LH20...
Page 64: Front Pwb Assembly (Ir And Led Control) Layout (Back View)
Front PWB Assembly (IR and LED Control) Layout (Back View) Front PWB Assembly (IR and LED Control) Layout (Back View) Control IC U1 IR Sensor (Power LEDs) POWER LEDS (LED1 through LED10) February 2009 42LH20...
Page 65 3.3V 3.3V 2.4V Key1 3.3V 3.3V Open Key2 3.3V 3.3V Open Key2 3.3V 3.3V Open 5V ST 5.1V 5.1V 1.5V 4.8V 4.8V 3.3V_ST 3.29V 3.29V Open POWER On/Off 3.29V Diode Mode values taken with all Connectors Removed February 2009 42LH20...
Page 66: Key Board Section
KEY BOARD SECTION KEY BOARD SECTION SW3001 SW3002 SW3003 SW3004 SW3005 SW3006 SW3007 SW3008 P3000 To Main PWB February 2009 42LH20...
Page 67 0.179V Input 0.906V Volume (+) 0.906V Menu 1.65V CH (Dn) 1.65V Enter 2.24V CH (Up) 2.24V P3000 Connector “Side Key" to “IR/LED Control PWB“ P1 Label STBY Diode Check Key1 3.3V 3.3V Open Key2 3.3V 3.3V Open February 2009 42LH20...
Page 68: Reassembly Notes
Pay attention to the wire dress for the Side Key PWB. These wires can get pinched between the rear cover and lower left hand screw post. The wires can be dressed to the right of the post in the slot provided. February 2009 42LH20...
Page 69 This section shows the 11X17 foldout that ’ s available in the Paper This section shows the 11X17 foldout that ’ s available in the Paper and Adobe version of the Training Manual. and Adobe version of the Training Manual. February 2009 42LH20...
Page 70 42LH20 INTERCONNECT DIAGRAM Warning: T-Con PWB under shield. Be sure to reinsert screws P801 “Main” to CN5 “T-CON” before operating set with shield removed. TO TFT MODULE TO TFT MODULE Diode Diode LABEL LABEL Check Check TXA1- 1.2V 1.1V 16.9V...
Page 71 42LH20 LVDS P801 WAVEFORMS LVDS P801 PIN 4 (OPC-Out) LVDS P801 PIN 6 (TXA3+) LVDS P801 PIN 7 (TXA3-) LVDS P801 PIN 9 (TXAC+) LVDS P801 PIN 10 (TXAC-) LVDS P801 PIN 12 (TXA2+) LVDS P801 PIN 13 (TXA2-) LVDS P801 PIN 15 (TXA1+)
Page 72 42LH20 Main Board (Front View) Component Layout 42LH20 Main Board (Front View) Component Layout IC704 IC705 Q706 IC704 P801 IC105 3.3V_FE 1.26V_VDDC IC1003 Q706 Switch 1 (5V) 3.3V-FE HDCP EEPROM 2 (0.48V) 1 (0.78V) To T-CON (12V LVDS) L726 3 (0.48V)
Page 73 42LH20 Main Board (Rear View) Component Layout 42LH20 Main Board (Rear View) Component Layout IC1003 P801 IC1003 To Tuner 5V Q104 Regulator Q104 Power Det Q102 Q103 1 (12V) Q102 B 0.08V 2 (Gnd) Power Det 12V C 3.3V 3 (8.94V) B 0.78V...
Page 74 42LH20 42LH20 Direct View LCD This concludes the 42LH20 training session.

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