LG 55QNED81SRA Service Manual
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LG 55QNED81SRA Service Manual

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LED TV
SERVICE MANUAL
CHASSIS : UB32B
MODEL : 55QNED81SRA
CAUTION
BEFORE SERVICING THE CHASSIS, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.
P/NO : MFL71988257 (2302-REV00)
Any reproduction, duplication, distribution (including by way of email, facsimile or other electronic means),
publication, modification, copying or transmission of this Service Manual is STRICTLY PROHIBITED unless you
have obtained the prior written consent of the LG Electronics entity from which you received this Service Manual.
The material covered by this prohibition includes, without limitation, any text, graphics or logos in this Service
Manual.
Copyright © 2023 LG Electronics Inc. All rights reserved. Only training and service purposes.

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Summary of Contents for LG 55QNED81SRA

  • Page 1 Service Manual is STRICTLY PROHIBITED unless you have obtained the prior written consent of the LG Electronics entity from which you received this Service Manual. The material covered by this prohibition includes, without limitation, any text, graphics or logos in this Service Manual.
  • Page 2 BLOCK DIAGRAM ................. 11 EXPLODED VIEW .................. 12 WIRING DIAGRAM ................13 ASSEMBLY / DISASSEMBLY GUIDE ........... 14 TROUBLE SHOOTING GUIDE ..........APPENDIX - 2 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.

  • Page 3: Safety Precautions

    When the exposed metal has no return path to the chassis the reading must be infinite. An other abnormality exists that must be corrected before the receiver is returned to the customer. - 3 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.

  • Page 4: Servicing Precautions

    - 4 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.
  • Page 5 1. Clip each fuse or resistor lead at top of the circuit board hollow stake. 2. Securely crimp the leads of replacement component around notch at stake top. - 5 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.

  • Page 6: Specification

    * Some models do not support HDMI4 USB Input My Media(Movie/Photo/Music List) or SVC SPDIF out Optical Audio out Ethernet Connect AV Input CVBS, Audio L/R Only for INDIA - 6 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.

  • Page 7: Dtv Mode

    23.98 1188 7680*4320 1188 7680*4320 1188 7680*4320 131.87 29.97 1188 8K Model Only. 7680*4320 1188 7680*4320 2376 7680*4320 263.74 59.94 2376 7680*4320 2376 - 7 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.
  • Page 8 UHD DeepColor is On (UHD, 8K 120Hz models only), 2560*1440 182.99 119.99 497.7 Support only when UHD Deep- Color is On - 8 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.
  • Page 9 (6) After finishing the update, it will show a pop-up below the picture. (7) Click “Yes” : Tv will be turn off and on itself - 9 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.
  • Page 10 “The latest version of the SW is available for your TV. Do you want to update now” (3) [Yes] : update starts. [No] : Close the pop-up, check out later - 10 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.

  • Page 11: Block Diagram

    BLOCK DIAGRAM - 11 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.

  • Page 12: Exploded View

    It is essential that these special safety parts should be replaced with the same components as recommended in this manual to prevent Shock, Fire, or other Hazards. Do not modify the original design without permission of manufacturer. - 12 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.

  • Page 13: Wiring Diagram

    WIRING DIAGRAM - 13 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.
  • Page 14 ASSEMBLY / DISASSEMBLY GUIDE (SET) [Back Cover Disassembly Guide] . Lay the Set on a flat pad. (Disassemble the stand and power cord.) 2. Remove Screw. - 14 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.
  • Page 15 Back Cover with the palm of your hand. Separate each latch part slowly Guide Hole in the same way Slowly separate the latch part Remove the back cover. - 15 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.
  • Page 16 1) Disassemble the Cable(2ea) (2) Disassemble of Cover Shield 1) Disassemble the Screws 55” : 7ea (2) Disassemble the source PCB from the guide - 16 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.
  • Page 17 (3) Disassemble of Guide panel Disassemble the Screws. 55” : 11ea (4) Disassemble of Case Top Disassemble the Screws. 55” : 6ea - 17 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.
  • Page 18 2. The Guide of Panel assy (with Guide panel) (1) Disassemble of Guide panel Disassemble the Down Hooks. (2) Disassemble of Guide panel. Disassemble the Hooks. - 18 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.
  • Page 19 (3) Removal of LGP (4) Removal of Reflector (5) Removal of LED Housing Assy 55” : 19ea ■ Assemble in reverse order Step 10 ~ 1 - 19 - Copyright © LG Electronics Inc. All rights reserved. Only for training and service purposes.

  • Page 20: Troubleshooting Guide

    TROUBLE SHOOTING GUIDE Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 21 E. Noise Circuit noise, mechanical noise F. Exterior error Exterior defect First of all, Check whether there is SVC Bulletin in GSCS System for these model. Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 22 ☞A4 & A2 Always check & record S/W Version and White Replace Main Board Re-enter White Balance value Balance value before replacing the Main Board Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 23 ☞A9 Check various Check and No Video/ Normal voltages of Power replace No audio voltage? Board (12V…) MAIN B/D Replace Power Board and repair parts Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 24 1. Reconnection 2. Install Booster S/W Upgrade Contact with signal distributor Normal or broadcaster (Cable or Air) Picture? Normal Picture? Replace Main B/D Close Close Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 25 Replace Main/T-con B/D error cable normal Request repair for external device/cable Check external External HDMI device and device/Cable Replace Main/T-con B/D error cable normal Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 26 Replace (Check normal operation of HDMI/ Screen Main /T-con External Input, Component, normal? RGB and HDMI/DVI by connecting Jig, pattern Generator ,Set-top Box etc. Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.

  • Page 27: Power Error

    Measure voltage of each output of Power B/D Normal? Normal Replace Main B/D voltage? Normal Close Check Power ST-BY 7.8V voltage? ☞A9 Replace Power B/D Replace Power Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 28 Normal Replace Main B/D Check Power B/D voltage? voltage ※ Caution Check and fix exterior Replace Power B/D of Power B/D Part Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 29 Wireless model only Process/SVC F0~F9, FA~FZ Process/SVC Records (in-stop, Power Only etc) Normal Case - N/A Records Initial value Initial value not recorded yet Normal Case Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 30 Screen normal of Power Board voltage Speaker off Cancel OFF Replace Power Board and repair parts Check Speaker Replace MAIN Board Disconnection disconnection Replace Speaker Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 31 (In case of Connect and check External Input Normal other external signal error) audio? device Check and fix external device Check and fix external device Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.

  • Page 32: Function Error

    Replace Main B/D (Power B/D don’t have problem) If R/C operate, Normal Close operating? Explain the customer cause is interference from light in room. Replace R/C Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 33 Down load the Firmware * If you conduct the loop at 3times, change the MR23. * INSTART MENU  14.RF Remote control Test  3. Firmware download Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 34 Main B/D INSTART menu is “NG”? ☞A15 Close Check & Repair Wifi cable connection ☞A4 Wi-Fi Mac value Close is “NG”? Change the Wifi assy Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 35 Recognition error - S/W Version HDMI/ Check and fix DVI, Optical Replace Main B/D Fix in Recognition external device/cable accordance error with technical information Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 36 Cable Make the Connect network function ‘on’ Close Close Change Voice Cable Connection Recognition Change Main B/D Is OK? Ass’y Close Re-connect Close Cable Close Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 37 “Part related to nose” in the Owner’s then proceed as shown in the solution manual Manual. (For models without any fix information, provide the description) Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 38 Revised date 17/17 Zoom part with Module Replace module exterior damage damage Cabinet Replace cabinet damage Remote control Replace remote control damage Stand Replace stand dent Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 39 Exchange Module (1) ~ (3) A-6/11 ~ 8/11 Module Exchange T-Con (1) ~ (2) A-9/11 ~ 10/11 Exchange Power Board(PSU) A-11/11 Continue to the next page Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 40 How to use the Service remote control A16-A18 Check items after Main B/D replacement E. Etc Adjustment Test pattern - ADJ Key F. WIFI/RF How to check WIFI/RF Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 41 Content Check Back Light On with naked eye date If the Black light LED assemble is ‘OK’, you can see the lights on each points. Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 42 2. Enter into White Balance. 3. After recording the R, G, B (GAIN, Cut) value of Color Temp (Cool/Medium/Warm), re-enter the value after replacing the MAIN BOARD. Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 43 TUNER input signal strength checking method date  General  Programmes Programme Tuning  Manual Tuning When the signal is strong, use the attenuator (-10dB, -15dB, -20dB etc.) Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 44 Revised Content Version checking method date 1. Checking method for remote control for adjustment Version Press the IN-START with the remote control for adjustment Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 45 1. Check the signal strength or check whether the screen is normal when the external device is connected. 2. After measuring each voltage from power supply, finally replace the MAIN BOARD. Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 46 Revised Content connection diagram date As the part connecting to the external input, check the screen condition by signal Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 47 A. Video error_Color error symptom date Revised Content Check Link Cable(CEDS) reconnection condition date Check the contact condition of the Link Cable, especially dust or mis insertion. Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 48 Screen darkness to disconnection of the FFC cable pin. G color transient due to poor FFC cable CABLE G Color Excessive connection A - 1/11 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 49 LVDS cable connection problem CABLE Color spread LVDS cable connection problem Due to foreign substance withi nLVDS CABLE Screen stop cable PIN A - 2/11 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 50 Main IC problem Main Dark picture Dark left-side screen Top/bottom screen part Main Broken picture Picture problem due to tuner Inner side quality problem A - 3/11 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 51 Screen spread Screen corner appears blurry Main Color Spread Color spread on the screen Main Blurry Screen Blurry picture on the screen A - 4/11 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 52 Screen picture spread problem Screen problem No problem at the initial stage. Right-side Main During Heat run, right-side picture picture problem problem A - 5/11 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 53 BLU internal foreign matter inflow MODULE Internal matter 6 block image broken MODULE Image broken MODULE Image broken Screen sync signal broken A - 6/11 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 54 BLU Vertical spreading on cube screen in no MODULE Vertical smear signal MODULE Over color Screen contour part brightly Over color A - 7/11 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 55 Center of the screen 1 block dark MODULE Screen darkness MODULE Vertical bar Center Vertical Bar Darkness at the MODULE bottom of the MODULE internal BLU breakage screen A - 8/11 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 56 T-Con is defective and the picture below T-CON image broken the screen is broken A - 9/11 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 57 The entire screen is dark and bit noise T-CON Image Broken occurs The entire screen is dark and bit noise T-CON Image Broken occurs A - 10/11 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 58 Appendix : Exchange Power Board (PSU) #11 Check parts by symptom No Light No Power On A - 11/11 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 59 Established B. Power error _No power symptom date Revised Content Check front Power Indicator date ST-BY condition: On or Off Power ON condition: Turn Off Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 60 - SET St-by : 0V 5. LED voltage Check : P801, 8 pin & P802, 1 pin All condition meets, Power Board OK. SK100 (AC input) Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 61 POWER OFF MODE checking method date Entry method 1. Press the IN-START button of the remote control for adjustment. 2. Check the entry into adjustment item 3. Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.

  • Page 62: Checking Method

    1. Press the Setting button on the remote control. 2. Select the Sound function of the Menu. 3. Select the Sound Out. 4. Select TV Speaker. Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 63 3. Connect the tester RX1 to the speaker terminal and if you hear the ‘Chik~ Chik~’ SPK_L+FT sound when you touch the GND and output terminal, the speaker is normal. Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 64 Checking order 1. Check IR cable condition between IR & Main board.(Check picture number① and ②.) 2. Check the standby 3.5V on the terminal. (③) Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 65 Checking order to check motion remote/wifi Checking order 1. Check BT/Wifi cable condition between BT/Wifi assy & Main board. 2. Check the 3.5V on the terminal 1 pin. Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 66 E. Etc symptom date Revised Content How to use the Service remote control date 1. How to access the remote control 1 page 2 page Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 67 Digital EYE function ON/OFF For some Model, access to the Test Pattern TILT Used for screen tilting change (Access to the old PDP control mode) Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 68 Connects to external input 1,2,3 COMP1,2 (Added function) Connects to Component 1,2 HDMI1,2,3,4 Connects to HDMI 1,2,3,4 (Add function) DVI (Add function) Connects to DVI Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.

  • Page 69: White Noise

    ID label on the back cover. ※ You can select the menu in the white noise state Back key(long press – 3sec) White Noise Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 70 You can view 11 types of patterns using the ADJ Key Checking item : 1. Defective pixel 2. Residual image 3. MODULE error (ADD-BAR,SCAN BAR..) 4. Video error (Classification of MODULE or Main-B/D!) Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 71 Standard Repair Process Detail Technical Manual Error Established F. WIFI /RF symptom date Revised Content How to Check Wifi / RF date WiFi / Magic Search 2 page Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 72 If the result comes out ‘NG’ for each part, make sure to check the connector check again between the part and the cable is properly connected. (Check if the cable connection is normal) 1 / 1 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 73 (Some models launched before 2017 may have 5V / 3.5V) 3. If the result comes out ’NG’, replace Power Board ● Note. 1 / 4 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 74 2. Check the output voltage of 20VS and 12VM 3. If the result comes out ’NG, check the voltage of PWR_ON ● Note. 2 / 4 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 75 3. If the result comes out ’NG, replace Main Board. If it comes out ‘OK’, replace Power B/D 4. The normal power supply from MAIN to POWER is 3V or higher ● PWR_ON Note. 3 / 4 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 76 2. If the result comes out ’NG, replace Power B/D. If it comes out ‘OK’, check if Main B/D and Module operate normally. Note. 4 / 4 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 77 Connect the T-Con ~ motherboard FFC cable to the Jig A jig for sending test patterns ※ SVC Part P/No : RAD33749101 Parts connecting Cable Appendix. 1 / 1 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.
  • Page 78 VDD-EPI / 2 HVDD HVDD uses half the voltage of VDD-EPI (7.7V~8.1V) VDD-EPI 16.2V ~ 16.8V HVDD 32V ~ 36V VGH1 VCC1.8 Appendix. 1 / 1 Copyright © 2023 LG Electronics. Inc. All rights reserved. Only for training and service purposes.

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