Dell Latitude 7420 Service Manual
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Dell Latitude 7420 Service Manual

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Latitude 7420
Service Manual
Regulatory Model: P135G/P136G
Regulatory Type: P135G001/P136G001
January 2021
Rev. A00

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Summary of Contents for Dell Latitude 7420

  • Page 1 Latitude 7420 Service Manual Regulatory Model: P135G/P136G Regulatory Type: P135G001/P136G001 January 2021 Rev. A00...
  • Page 2 A WARNING indicates a potential for property damage, personal injury, or death. © 2021 Dell Inc. or its subsidiaries. All rights reserved. Dell, EMC, 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 Chapter 2: Removing and installing components................11 Recommended tools................................11 Screw List.....................................11 Major components of your system..........................
  • Page 4 Clearing BIOS (System Setup) and System passwords...................77 Chapter 5: Troubleshooting......................78 Recovering the operating system..........................78 Backup media and recovery options..........................78 Dell SupportAssist Pre-boot System Performance Check diagnostics..............78 Running the SupportAssist Pre-Boot System Performance Check..............79 Diagnostic LED behavior..............................79 Real-Time Clock (RTC Reset)............................80 Flashing BIOS (USB key)..............................
  • Page 5 Flashing the BIOS................................81 WiFi power cycle................................81 BIOS recovery..................................82 BIOS recovery using hard drive..........................82 BIOS recovery using USB drive..........................83 M-BIST....................................83 LCD Built-in Self Test (BIST)............................84 Chapter 6: Getting help.......................85 Contacting Dell.................................. 85 Contents...

  • Page 6: Chapter 1: Working On Your Computer

    Damage due to servicing that is not authorized by Dell is not covered by your warranty. Read and follow the safety instructions that came with the product.
  • 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 that all field service technicians 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 that technicians keep sensitive parts separate from all insulator parts while performing service and that they use anti-static bags for transporting sensitive components.

  • Page 11: 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 12 Table 1. Screw list (continued) Component Screw type Quantity Image 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 M2x2 M2.5x5...
  • Page 13 Table 1. Screw list (continued) Component Screw type Quantity Image Keyboard M1.6x1.7 M2x2 Removing and installing components...

  • Page 14: Major Components Of Your System

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

  • Page 15: 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 16: 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 17: 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 18: 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 19 About this task Removing and installing components...

  • Page 20: 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 21 Removing and installing components...

  • Page 22: Solid-State Drive

    Steps 1. Connect the battery cable. 2. Align and place the base cover on the computer, and snap the base cover latches into place. 3. Tighten the eight captive screws to secure the base cover to the computer. Next steps 1.

  • 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 on the top left corner. 2. Loosen the single (M2x2.5) screw and remove the WWAN-card bracket. 3.

  • 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 lithium-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: Heatsink Assembly

    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: Palmrest Antenna Module

    Palmrest antenna module Removing the palmrest antenna module Prerequisites 1. Follow the procedure in before working inside your computer. 2. Remove the microSD card. 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.

  • Page 35: Display Assembly

    About this task The following image indicates the location of the palmrest antenna module and provides a visual representation of the installation procedure. Steps 1. Place the palmrest antenna module on the system and replace the two (M2x2.5) screws that secure it to the system. 2.
  • Page 36 About this task The following images indicate the location of the display assembly and provide a visual representation of the removal procedure. Removing and installing components...
  • Page 37 Steps 1. Remove the single (M2x2) securing the WLAN card bracket to the antenna cables. 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

    8. Open the display lid to 90º angle and remove the four (M2.5x5) screws securing the hinges to the palmrest assembly. 9. Remove the display assembly from the computer. NOTE: NOTE: The display assembly is a Hinge-Up Design (HUD) assembly and cannot be further disassembled once it is removed from the bottom chassis.
  • Page 39 Removing and installing components...

  • Page 40: Audio Board

    Steps 1. Align and place the display assembly at a convenient angle to the bottom chassis. 2. Replace the four (M2.5x5) 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

    4. Remove the base cover. 5. Remove the battery. 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 and peel the audio board FFC from the system board. 2.

  • 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. Next steps 1. Install the battery. 2.

  • 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 1. Release the cable from the tabs on the palmrest assembly. 2. Lift and remove the speakers from the computer chassis. Installing the speaker Prerequisites If you are replacing a component, remove the existing component before performing the installation procedure.

  • 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 9. Remove the heatsink assembly. 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 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. Enter the service mode. 3. Remove the microSD card. 4. Remove the card. 5. Remove the base cover. 6. Remove the solid-state drive.

  • 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

    4. Remove the card. 5. Remove the base cover. 6. Remove the solid-state drive. 7. Remove the WWAN card. 8. Remove the battery. 9. Remove the heatsink assembly. 10. 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 7. Remove the heatsink assembly. 8. Remove the audio board. 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

    Downloading Windows drivers Steps 1. Turn on the notebook. 2. Go to Dell.com/support. 3. Click Product Support, enter the Service Tag of your notebook, and then click Submit. NOTE: If you do not have the Service Tag, use the auto detect feature or manually browse for your notebook model.

  • Page 63: Chapter 4: System Setup

    Boot menu Press <F12> when the Dell logo appears to initiate a one-time boot menu with a list of the valid boot devices for the system. Diagnostics and BIOS Setup options are also included in this menu. The devices listed on the boot menu depend on the bootable devices in the system.

  • Page 64: Navigation Keys

    Boot sequence enables you to bypass the System Setup–defined boot device order and boot directly to a specific device (for example: optical drive or hard drive). During the Power-on Self-Test (POST), when the Dell logo appears, you can: ● Access System Setup by pressing F2 key ●...
  • Page 65 Table 2. System setup options—System information menu (continued) Overview Signed Firmware Update Displays whether the Signed Firmware Update is enabled on your system. Battery Information Primary Displays that battery is primary. Battery Level Displays the battery level of the system. Battery State Displays the battery state of the system.
  • Page 66 Table 3. 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 5. System setup options—Storage menu (continued) Storage By default, the Secure Digital (SD) Card Read-Only Mode option is not enabled. Table 6. 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 9. 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. System setup...
  • Page 72 Table 12. 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 14. 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 In Windows

    If BitLocker is enabled, it must be suspended prior to updating the system BIOS, and then re enabled after the BIOS update is completed. Steps 1. Restart the computer. 2. Go to Dell.com/support. ● Enter the Service Tag or Express Service Code and click Submit. ● Click Detect Product and follow the instructions on screen. System setup...

  • Page 75: Updating Bios On Systems With Bitlocker Enabled

    3. Insert the USB flash drive into the computer that requires the BIOS update. 4. Restart the computer and press F12 when the Dell logo appears to display the One Time Boot Menu. 5. Using arrow keys, select USB Storage Device and press Enter.

  • Page 76: System And Setup Password

    Figure 2. DOS BIOS Update Screen System and setup password Table 18. System and setup password Password type Description System password Password that you must enter to log on to your system. Setup password Password that you must enter to access and make changes to the BIOS settings of your computer.

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

    1. Key in your computer's service tag number into the locked BIOS/system setup screen. 2. Convey the code generated to the Dell Tech Support agent. 3. The Dell Tech Support agent will provide a 32 character Master System Password that can be used to access the locked BIO/system setup.

  • Page 78: Chapter 5: Troubleshooting

    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 79: Running The Supportassist Pre-Boot System Performance Check

    Running the SupportAssist Pre-Boot System Performance Check Steps 1. Turn on your computer. 2. As the computer boots, press the F12 key as the Dell logo appears. 3. On the boot menu screen, select the Diagnostics option. 4. Click the arrow at the bottom left corner.

  • Page 80: Real-Time Clock (Rtc Reset)

    Real-Time Clock (RTC Reset) The Real Time Clock (RTC) reset function allows you or the service technician to recover Dell Latitude, systems from No POST/No Power/No Boot situations. The legacy jumper enabled RTC reset has been retired on these models.

  • Page 81: Flashing Bios (Usb Key)

    4. Connect the bootable USB drive to the computer that needs the BIOS update. 5. Restart the computer and press F12 when the Dell logo is displayed on the screen. 6. Boot to the USB drive from the One Time Boot Menu.

  • Page 82: Bios Recovery

    BIOS recovery using hard drive About this task NOTE: Ensure that you have the previous version and the latest version of the BIOS from the Dell support site available to use. NOTE: Ensure that you have the file type extensions visible in the operating system (OS).

  • Page 83: Bios Recovery Using Usb Drive

    Ensure that you have the file type extensions visible in the operating system. NOTE: Ensure that you have downloaded the latest BIOS from the Dell support site and save it on your system. Steps 1. Browse to the location of the downloaded BIOS update executable (.exe) file.

  • Page 84: Lcd Built-In Self Test (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 85: Chapter 6: Getting Help

    About this task Dell provides several online and telephone-based support and service options. Availability varies by country and product, and some services may not be available in your area. To contact Dell for sales, technical support, or customer service issues: Steps 1.

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