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Dell Latitude 7420 Service Manual

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Latitude 7420/Latitude 7420 2-in-1
Service Manual
Regulatory Model: P135G/P136G
Regulatory Type: P135G001/P136G001
July 2023
Rev. A04

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Summary of Contents for Dell Latitude 7420

  • Page 1 Latitude 7420/Latitude 7420 2-in-1 Service Manual Regulatory Model: P135G/P136G Regulatory Type: P135G001/P136G001 July 2023 Rev. A04...
  • Page 2 A WARNING indicates a potential for property damage, personal injury, or death. © 2021-2023 Dell Inc. or its subsidiaries. All rights reserved. Dell Technologies, Dell, and other trademarks are trademarks of Dell Inc. or its subsidiaries. Other trademarks may be trademarks of their respective owners.

  • Page 3: Table Of Contents

    Contents Chapter 1: Working on your computer................... 6 Safety instructions................................6 Service mode.................................. 6 Before working inside your computer........................8 Safety precautions................................ 9 Electrostatic discharge—ESD protection....................... 9 ESD field service kit ..............................10 Transporting sensitive components......................... 11 After working inside your computer......................... 11 Chapter 2: Removing and installing components................
  • Page 4 Deleting or changing an existing system setup password................. 77 Clearing BIOS (System Setup) and System passwords...................77 Chapter 5: Troubleshooting......................78 Handling swollen rechargeable Li-ion batteries......................78 Dell SupportAssist Pre-boot System Performance Check diagnostics..............79 Running the SupportAssist Pre-Boot System Performance Check..............79 Contents...
  • Page 5 LCD Built-in Self Test (BIST)........................... 80 System-diagnostic lights..............................81 Recovering the operating system..........................82 Real-Time Clock (RTC Reset)............................82 Backup media and recovery options..........................83 Wi-Fi power cycle................................83 Drain residual flea power (perform hard reset)......................83 Chapter 6: Getting help and contacting Dell................85 Contents...

  • Page 6: Chapter 1: Working On Your Computer

    You should only perform troubleshooting and repairs as authorized or directed by the Dell technical assistance team. Damage due to servicing that is not authorized by Dell is not covered by your warranty. See the safety instructions that is shipped with the product or at www.dell.com/regulatory_compliance.
  • Page 7 3. [For models configured with an Owner Tag] When the Owner Tag information appears on the screen, press any key to proceed. NOTE: The Service Mode procedure will automatically skip this step if the Owner Tag of the system is not set up in advance by the manufacturer.

  • Page 8: Before Working Inside Your Computer

    5. When the ready-to-proceed message appears on the screen, press any key to proceed. The system emits three short beeps and shuts down immediately. Once the system shuts down, you can perform replacement procedures without disconnecting the battery cable from the system board.

  • Page 9: Safety Precautions

    ESD protection is an increasing concern. Due to the increased density of semiconductors used in recent Dell products, the sensitivity to static damage is now higher than in previous Dell products. For this reason, some previously approved methods of handling parts are no longer applicable.

  • Page 10: Esd Field Service Kit

    It is recommended to use the traditional wired ESD grounding wrist strap and protective anti-static mat at all times when servicing Dell products. In addition, it is critical to keep sensitive parts separate from all insulator parts while performing service and that they use anti-static bags for transporting sensitive components.

  • Page 11: Transporting Sensitive Components

    Transporting sensitive components When transporting ESD sensitive components such as replacement parts or parts to be returned to Dell, it is critical to place these parts in anti-static bags for safe transport. After working inside your computer About this task NOTE: Leaving stray or loose screws inside your computer may severely damage your computer.

  • Page 12: Chapter 2: Removing And Installing Components

    Removing and installing components NOTE: The images in this document may differ from your computer depending on the configuration you ordered. Topics: • Recommended tools • Screw List • Major components of your system • micro-SD card • SIM card tray •...
  • Page 13 Table 1. Screw list  Component Screw type Quantity Image Base cover Captive screws NOTE: Screws are part of the base cover. Solid-state drive M2x2 WWAN M2x2.5 3-cell Battery M2.5x4 Captive screws 4-cell Battery M2x4 Captive screws Heatsink assembly M2x2.5 Palmrest antenna M2x2 M2x2.5 Display assembly...
  • Page 14 Table 1. Screw list (continued) Component Screw type Quantity Image Power button with fingerprint reader M1.6x1.7 Keyboard M1.6x1.7 M2x2 Removing and installing components...

  • Page 15: Major Components Of Your System

    Major components of your system 1. Base cover Removing and installing components...

  • Page 16: Micro-Sd Card

    18. WWAN card NOTE: Dell provides a list of components and their part numbers for the original system configuration purchased. These parts are available according to warranty coverages purchased by the customer. Contact your Dell sales representative for purchase options.

  • Page 17: Installing The Micro-Sd Card

    Installing the micro-SD card Prerequisites If you are replacing a component, remove the existing component before performing the installation procedure. About this task The following image indicates the location of the micro-SD card reader slot and provides a visual representation of the installation procedure.

  • Page 18: Installing The Sim Card Tray

    Steps 1. Insert a pin into the release hole to release the SIM card tray. 2. Push the pin to disengage the lock, and eject the SIM card tray. 3. Slide the SIM card tray out of the slot on the system. 4.

  • Page 19: Base Cover

    Steps 1. Align and place the SIM card in the dedicated slot on the SIM card tray. 2. Slide the SIM card tray into the slot in the system [6], and push it to lock in place. Next steps Follow the procedure in After working on your computer.
  • Page 20 About this task Removing and installing components...

  • Page 21: Installing The Base Cover

    Steps 1. Loosen the eight captive screws that secure the base cover to the computer. 2. Use a plastic scribe to pry open the base cover, starting from the U-shaped recesses near the hinges at the top edge of the base cover.

  • Page 22: Solid-State Drive

    Steps 1. Align and place the base cover on the computer, and snap the base cover latches into place. 2. Tighten the eight captive screws to secure the base cover to the computer. Next steps 1. Install the microSD card. 2.

  • Page 23: Installing The Solid-State Drive

    Steps 1. Remove the screw (M2x2) that secures the SSD shield and remove the shield from the SSD. 2. Remove the screw (M2x2) that secures the SSD to the system board. 3. Slide and remove the solid-state drive from the M.2 slot on the system board. NOTE: A thermal pad is included with the SSD plate and must always be adhered to the plate.

  • Page 24: Wwan Card

    Steps 1. Align the notch on the SSD with the tab on the M.2 slot and slide the SSD into the M.2 card slot on the system board. 2. Replace the screw (M2x2) that secures the SSD to the system board. 3.
  • Page 25 Steps 1. Using a plastic scribe, pry and remove the WWAN card shield covering the WWAN card. NOTE: Pry open the WWAN card shield from the recess. 2. Loosen the single (M2x2.5) screw and remove the WWAN-card bracket. 3. Disconnect the antenna cables from the connectors on the WWAN card. 4.

  • Page 26: Installing The Wwan Card

    Installing the WWAN card Prerequisites If you are replacing a component, remove the existing component before performing the installation procedure. About this task The following image indicates the location of the WWAN card and provides a visual representation of the installation procedure. Steps 1.

  • Page 27: Battery

    ● If the battery gets stuck inside your computer as a result of swelling, do not try to release it as puncturing, bending, or crushing a rechargeable Li-ion battery can be dangerous. In such an instance, contact Dell technical support for assistance. See www.dell.com/contactdell.

  • Page 28: Installing The 3-Cell Battery

    About this task The following images indicate the location of the battery and provide a visual representation of the removal procedure. Steps 1. Disconnect the battery cable from the system board. 2. Disconnect the speaker cable from the speaker board and release the speaker cable from the routing guides over the upper right side of the battery.
  • Page 29 About this task The following image indicates the location of the battery and provides a visual representation of the installation procedure. NOTE: If the battery is disconnected from system board, there is delay during computer boot as the computer undergoes RTC reset.

  • Page 30: Removing The 4-Cell Battery

    Removing the 4-cell battery Prerequisites 1. Follow the procedure in before working inside your computer. 2. Remove the microSD card. 3. Remove the base cover. NOTE: If the battery is disconnected from system board, there is delay during computer boot as the computer undergoes RTC reset.

  • Page 31: Installing The 4-Cell Battery

    4. Lift the battery and remove the battery from the computer. Installing the 4-cell battery Prerequisites If you are replacing a component, remove the existing component before performing the installation procedure. About this task The following image indicates the location of the battery and provides a visual representation of the installation procedure. NOTE: If the battery is disconnected from system board, there is delay during computer boot as the computer undergoes RTC reset.

  • Page 32: Heat Sink

    3. Connect the speaker cable to the speaker board and reroute the speaker cable into its routing channel over the upper right side of the battery. 4. Connect the battery cable to the system board. Next steps 1. Install the base cover.

  • Page 33: Installing The Heatsink Assembly

    Installing the heatsink assembly Prerequisites If you are replacing a component, remove the existing component before performing the installation procedure. About this task The following image indicates the location of the heatsink assembly and provides a visual representation of the installation procedure.

  • Page 34: Installing The Palmrest Antenna Module

    3. Remove the base cover. About this task The following images indicate the location of the palmrest antenna module and provide a visual representation of the removal procedure. Steps 1. Remove the (M2x2) screw that secures the WLAN bracket to the system board. 2.

  • Page 35: Display Assembly

    Steps 1. Place the palmrest antenna module on the system and replace the two (M2x2.5) screws that secure it to the system. 2. Reroute the antenna cables through the routing channel and connect them to the WLAN module on the system board. 3.
  • Page 36 Removing and installing components...
  • Page 37 Steps 1. Remove the single (M2x2) securing the WLAN card bracket to the system board. 2. Lift the bracket from the WLAN card module on the system board. 3. Disconnect the WLAN antenna cables from the WLAN module. 4. Disconnect the WWAN antenna cable and release the cable from the rubber guides on the system board. 5.

  • Page 38: Installing The Display Assembly

    Figure 1. Display assembly with antennae cables Installing the display assembly Prerequisites If you are replacing a component, remove the existing component before performing the installation procedure. About this task The following image indicates the location of the display assembly and provides a visual representation of the installation procedure.
  • Page 39 Removing and installing components...

  • Page 40: Audio Board

    Steps 1. Align and place the display assembly at a 90º angle to the bottom chassis. 2. Replace the four (M2.5x4) screws securing the hinges to the bottom chassis. 3. Route the display cable along the guiding tabs and connect the display, camera, touch screen, sensor board cables to the system board.

  • Page 41: Installing The Audio Board

    About this task The following images indicate the location of the audio board and provide a visual representation of the removal procedure. Steps 1. Disconnect the speaker cable from the system board. 2. Disconnect and peel the audio board FFC from the system board. 3.

  • Page 42: Speakers

    Steps 1. Align and replace the audio board into its slot in the computer. 2. Replace the M2x2.5 screw to secure the audio board to the computer. 3. Connect the audio board FFC to the system board. 4. Connect the speaker cable to the system board. Next steps 1.

  • Page 43: Installing The Speaker

    About this task The following images indicate the location of the speakers and provide a visual representation of the removal procedure. Steps NOTE: The speaker cable is already disconnected from the system board. Release the cable from the tabs on the palmrest assembly. 2.

  • Page 44: Smartcard Reader

    Steps 1. Replace the speaker into the slot in the computer. 2. Route the speaker cable along the cable guides on the palmrest assembly. NOTE: While replacing the speakers, route the speaker cable into the routing channels along the bottom side of the palmrest assembly.
  • Page 45 2. Remove the microSD card. 3. Remove the base cover. 4. Remove the battery. 5. Remove the speaker. About this task The following images indicate the location of the smart card reader and provide a visual representation of the removal procedure.

  • Page 46: Installing The Smart Card Reader

    Steps 1. Disconnect the touchpad module and peel the FFC cable from over the touchpad module. 2. Disconnect the smart card reader and NFC module cables from the USH board. 3. Remove the four (M2x2.5) screws and slide the smart card reader out from its slot in the chassis. Installing the smart card reader Prerequisites If you are replacing a component, remove the existing component before performing the installation procedure.

  • Page 47: System Board

    Steps 1. Slide the smart card reader into its slot in the computer chassis and secure it using the four (M2x2.5) screws. 2. Adhere the smart card reader and NFC module cable and connect it to the USH board. 3. Adhere the touchpad FFC cable along the sides of the touchpad module and connect it to the system board. Next steps 1.
  • Page 48 CAUTION: Remove the heatsink assembly before removing the system board as there are two (M2x3) screws underneath the heatsink that secures the system board to the computer. NOTE: For configurations shipped with a carbon fiber palmrest and without WWAN antennas, the dummy SIM card tray must removed from the system before removing the system board.

  • Page 49: Installing The System Board

    Steps 1. Remove the single (M2x2.5) screw from the finger print reader bracket and remove the bracket from the computer. 2. Disconnect the fingerprint reader FPC from the system board. 3. Remove the single (M2x2) screw and lift the bracket from the WLAN antenna cables. 4.
  • Page 50 Removing and installing components...
  • Page 51 Steps 1. Replace the system board into the computer chassis and tighten it using the single (M2x2.5) screw (for computer configuration with fingerprint reader on power button) or four (M2x2.5) screws (for computer configuration without fingerprint reader), two (M2x4) screws, and two (M2x3) screws securing the system board in place. 2.

  • Page 52: I/O Board

    I/O board Removing the I/O board Prerequisites 1. Follow the procedure in before working inside your computer. 2. Remove the microSD card. 3. Remove the card. 4. Remove the base cover. 5. Remove the solid-state drive. 6. Remove the WWAN card.

  • Page 53: Power Button With Fingerprint Reader

    About this task The following image indicates the location of the I/O board and provides a visual representation of the installation procedure. Steps 1. Replace the I/O board into its slot in the computer. 2. Secure the I/O board to the computer using two (M2x4) screws. Next steps 1.

  • Page 54: Installing The Power Button With Fingerprint Reader

    6. Remove the WWAN card. 7. Remove the battery. 8. Remove the heatsink assembly. 9. Remove the system board. About this task The following images indicate the location of the power button with fingerprint reader and provide a visual representation of the removal procedure.

  • Page 55: Keyboard

    Steps 1. Replace the power button with fingerprint reader into its slot in the computer. 2. Secure the power button with fingerprint reader to the computer using the two (M1.6x1.7) screws. Next steps 1. Install the system board. 2. Install the heatsink assembly.
  • Page 56 9. Remove the system board. 10. Remove the board. About this task The following images indicate the location of the keyboard and provide a visual representation of the removal procedure. Removing and installing components...

  • Page 57: Installing The Keyboard

    Steps 1. Peel the LED board FFC, USH board FFC, touchpad FFC and SmartCard reader FFC from the back of the keyboard. 2. Disconnect the keyboard FPC and keyboard backlight FPC from the touchpad module. 3. Remove the 26 (M1.6x1.7) screws that secure the keyboard assembly to the computer. 4.
  • Page 58 Removing and installing components...

  • Page 59: Palmrest Assembly

    Steps 1. Align and place the keyboard on the keyboard support plate and secure it using the two (M2x2) screw. 2. Replace the keyboard assembly in to its slot in the computer. 3. Connect the keyboard FPC and keyboard backlight FPC to the touchpad module. 4.

  • Page 60: Installing The Palmrest Assembly

    6. Remove the WWAN card. 7. Remove the battery. 8. Remove the heatsink assembly. 9. Remove the display assembly. 10. Remove the speaker. 11. Remove the smart card reader. 12. Remove the audio board. 13. Remove the system board. 14. Remove the board.
  • Page 61 3. Install the board. 4. Install the system board. 5. Install the audio board. 6. Install the smart card reader. 7. Install the speaker. 8. Install the display assembly. 9. Install the heatsink assembly. 10. Install the battery. 11. Install the WWAN card.

  • Page 62: Chapter 3: Software

    ● Windows 10 Home, 64-bit ● Windows 10 Pro, 64-bit ● Ubuntu 20.04 LTS, 64-bit Drivers and downloads When troubleshooting, downloading or installing drivers it is recommended that you read the Dell Knowledge Base article, Drivers and Downloads FAQ 000123347. Software...

  • Page 63: Chapter 4: Bios Setup

    BIOS setup CAUTION: Unless you are an expert computer user, do not change the settings in the BIOS Setup program. Certain changes can make your computer work incorrectly. NOTE: Depending on the computer and its installed devices, the items listed in this section may or may not be displayed. NOTE: Before you change BIOS Setup program, it is recommended that you write down the BIOS Setup program screen information for future reference.

  • Page 64: One Time Boot Menu

    Depending on your system and its installed devices, the items that are listed in this section may or may not appear. Table 3. System setup options—System information menu  Overview Latitude 7420 BIOS Version Displays the BIOS version number. Service Tag Displays the Service Tag of the system.
  • Page 65 Table 3. System setup options—System information menu (continued) Overview Primary Displays that battery is primary. Battery Level Displays the battery level of the system. Battery State Displays the battery state of the system. Health Displays the battery health of the system. AC Adapter Displays whether the AC adapter is connected or not.
  • Page 66 Table 4. System setup options—Boot Configuration menu  Boot Configuration Boot Sequence Boot mode Displays the boot mode. Boot Sequence Displays the boot sequence. Secure Digital (SD) Card Boot Enable or disable the SD card read-only boot. By default, the Secure Digital (SD) Card Boot option is not enabled. Secure Boot Enable Secure Boot Enable or disable the secure boot feature.
  • Page 67 By default, the Video/Power only on Type-C Ports option is disabled. Type-C Dock Override Enables to use connected Type-C Dell Dock to provide data stream with external USB ports disabled. When Type-C Dock override is enabled, the Video/Audio/Lan submenu is activated.
  • Page 68 Table 6. System setup options—Storage menu (continued) Storage By default, the Secure Digital (SD) Card Read-Only Mode option is not enabled. Table 7. System setup options—Display menu  Display Display Brightness Brightness on battery power Enable to set screen brightness when the system is running on battery power. Brightness on AC power Enable to set screen brightness when the system is running on AC power.
  • Page 69 By default, the Optimized option is enabled. USB Wake Support Wake on Dell USB-C Dock When enabled, connecting a Dell USB-C Dock will wake the system from standby. By default, the Wake on Dell USB-C Dock option is enabled. Block Sleep Enables to block entering sleep (S3) mode in the operating system.
  • Page 70 Table 10. System setup options—Security menu (continued) Security Clear Enables to clear the TPM owner information and returns the TPM to the default state. By default, the Clear option is disabled. PPI ByPass for Clear Commands Controls the TPM Physical Presence Interface (PPI). By default, the PPI ByPass for clear Commands option is disabled.
  • Page 71 By default, the option is enabled. Dell Auto operating system Recovery Controls the automatic boot flow for SupportAssist System Resolution Console Threshold and for Dell operating system Recovery Tool. By default, the threshold value is set to 2. BIOS setup...
  • Page 72 Table 13. System setup options—System Management menu  System Management Service Tag Display the Service Tag of the system. Asset Tag Create a system Asset Tag. AC Behavior Wake on AC Enable or disable the wake on AC option. By default, the option is disabled. Wake on LAN Wake on LAN Enable or disable the system to power on by special LAN signals when it...
  • Page 73 Table 15. System setup options—Pre-boot Behavior menu (continued) Pre-boot Behavior Enable Adapter Warnings Enable or disable the warning messages during boot when the adapters with less power capacity are detected. By default, the option is enabled. Warning and Errors Enable or disable the action to be done when a warning or error is encountered. By default, the Prompt on Warnings and Errors option is enabled.

  • Page 74: Updating The Bios

    For more information on this subject, search in the Knowledge Base Resource at www.dell.com/support. Steps 1. Go to www.dell.com/support. 2. Click Product support. In the Search support box, enter the Service Tag of your computer, and then click Search. BIOS setup...

  • Page 75: Updating The Bios In Linux And Ubuntu

    Updating the BIOS in Windows to download the latest BIOS setup program file. 2. Create a bootable USB drive. For more information, search in the Knowledge Base Resource at www.dell.com/support. 3. Copy the BIOS setup program file to the bootable USB drive.

  • Page 76: System And Setup Password

    Most of the Dell computers built after 2012 have this capability, and you can confirm by booting your computer to the F12 One-Time Boot Menu to see if BIOS FLASH UPDATE is listed as a boot option for your computer. If the option is listed, then the BIOS supports this BIOS update option.

  • Page 77: Deleting Or Changing An Existing System Setup Password

    Clearing BIOS (System Setup) and System passwords About this task To clear the system or BIOS passwords, contact Dell technical support as described at www.dell.com/contactdell. NOTE: For information on how to reset Windows or application passwords, refer to the documentation accompanying Windows or your application.

  • Page 78: Chapter 5: Troubleshooting

    ● Using a non-Dell or incompatible battery may increase the risk of fire or explosion. Replace the battery only with a compatible battery purchased from Dell that is designed to work with your Dell computer. Do not use a battery from other computers with your computer.

  • Page 79: Dell Supportassist Pre-Boot System Performance Check Diagnostics

    Check diagnostics About this task SupportAssist diagnostics (also known as system diagnostics) performs a complete check of your hardware. The Dell SupportAssist Pre-boot System Performance Check diagnostics is embedded with the BIOS and is launched by the BIOS internally. The embedded system diagnostics provides a set of options for particular devices or device groups allowing you to: ●...

  • Page 80: Lcd Power Rail Test (L-Bist)

    LCD Built-in Self Test (BIST) Dell laptops have a built-in diagnostic tool that helps you determine if the screen abnormality you are experiencing is an inherent problem with the LCD (screen) of the Dell laptop or with the video card (GPU) and PC settings.

  • Page 81: System-Diagnostic Lights

    (AC, battery, coin cell) and errors drain flea power by pressing and holding down power button for 3~5 seconds. CPU failure ● Run the Dell Support Assist/Dell Diagnostics tool. ● If problem persists, replace the system board. System board failure (included ●...

  • Page 82: Recovering The Operating System

    It enables you to diagnose hardware issues, repair your computer, back up your files, or restore your computer to its factory state. You can also download it from the Dell Support website to troubleshoot and fix your computer when it fails to boot into their primary operating system due to software or hardware failures.

  • Page 83: Backup Media And Recovery Options

    Backup media and recovery options It is recommended to create a recovery drive to troubleshoot and fix problems that may occur with Windows. Dell proposes multiple options for recovering Windows operating system on your Dell PC. For more information. see...
  • Page 84 NOTE: For more information about performing a hard reset, search in the Knowledge Base Resource at www.dell.com/ support. Troubleshooting...

  • Page 85: Chapter 6: Getting Help And Contacting Dell

    Getting help and contacting Dell Self-help resources You can get information and help on Dell products and services using these self-help resources: Table 22. Self-help resources  Self-help resources Resource location Information about Dell products and services www.dell.com My Dell app...

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Latitude 7420 2-in-1P135gP136g

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