Enabling US Bands

Warning

This guide is for MT6761 (Helio A22) devices only. If you have an MT8766 processor, see the MT8766 disclaimer before proceeding.

Overview

Enable additional US LTE bands on the Qin F21 Pro by transplanting modem configuration from the Qin F30, a US-market variant. This modification adds support for bands 2, 4, 12, 13, 17, 66, and 71—enabling compatibility with major US carriers like T-Mobile and Verizon.

What you’ll accomplish

  • Enable US LTE bands (2, 4, 12, 13, 17, 66, 71)

  • Improve compatibility with US carriers

  • Maintain device functionality

Danger

Advanced Modification: This requires an unlocked bootloader and flashing critical system partitions. Errors can result in lost network connectivity or device brick. Windows PC required.

This guide uses modem files from the Qin F30, community-extracted scatter files, SP Flash Tool for flashing, and SN Write Tool for identifier restoration.

Understanding the Modification

The F30 Connection

The Qin F30 is a US-market variant of the F21 Pro with identical hardware but US-optimized cellular bands. This modification replaces three NV partitions (nvram, nvdata, nvcfg) and the modem image (md1img_a) with F30 versions, enabling frequencies already supported in hardware but disabled in software.

Supported Bands After Modification

  • LTE Band 2 (1900 MHz) - AT&T, T-Mobile, Verizon

  • LTE Band 4 (1700/2100 MHz) - T-Mobile, AT&T

  • LTE Band 12 (700 MHz) - T-Mobile extended range

  • LTE Band 13 (700 MHz) - Verizon primary

  • LTE Band 17 (700 MHz) - AT&T primary

  • LTE Band 66 (AWS) - T-Mobile, AT&T capacity

  • LTE Band 71 (600 MHz) - T-Mobile extended range

Hardware Limitations

The F21 Pro’s antenna design was optimized for Chinese frequencies. Bands 12, 13, 17, and 71 (lower frequencies) often show weaker reception than US-designed phones. Bands 2, 4, and 66 typically perform better. Performance is adequate in strong signal areas but may struggle in fringe coverage.

Prerequisites

Software & Tools (Windows Only)

  • Windows PC (7 or newer, 64-bit recommended)

  • Python (latest version, with “Add to PATH” enabled)

  • MTKClient

  • SP Flash Tool

  • SN Write Tool

  • MediaTek USB VCOM drivers

  • F30 US Bands Package (modem files, scatter file, databases)

Device Requirements

Critical: Record Your Identifiers

Danger

DO NOT SKIP: Flashing F30 partitions overwrites your unique identifiers with dummy values. You must record and restore them.

Record These Values

Navigate to Settings → About Phone and record:

  • IMEI (15 digits, usually starts with 86…)

  • Wi-Fi MAC address (format: XX:XX:XX:XX:XX:XX)

  • Bluetooth address (format: XX:XX:XX:XX:XX:XX)

Save these in a text file named my-f21-identifiers.txt. You’ll enter them manually into SN Write Tool later.

Installation Steps

Step 1: Install Prerequisites

  1. Install Python:

    # Download from python.org
# Check "Add Python to PATH" during installation
python --version

  2. Install MTKClient:

    cd C:\mtkclient
pip3 install -r requirements.txt

  3. Install MediaTek USB VCOM drivers

    • Run installer from extracted package

    • Restart computer after installation

  4. Extract SP Flash Tool to C:\SPFlashTool

  5. Extract SN Write Tool from F30 package

Step 2: Back Up NV Partitions

Create recovery backups before modification:

  1. Power off device

  2. Run backup command:

    cd C:\mtkclient
python mtk r nvram,nvdata,nvcfg nvram_backup.bin,nvdata_backup.bin,nvcfg_backup.bin

  3. Enter BROM mode:

    • Hold Volume Up + Volume Down

    • While holding, plug in USB cable

    • Keep holding until MTKClient detects device

  4. Wait for completion (1-2 minutes)

Optional full backup:

python mtk rl --skip userdata f21_full_backup

Step 3: Flash F30 Modem and NV Partitions

  1. Launch SP Flash Tool:

    • Run flash_tool.exe as Administrator

    • Click Scatter-loading

    • Select MT6761_Android_scatter.txt from F30 package

  2. Configure partitions:

    • UNCHECK ALL partitions

    • Check ONLY these four:

      • nvcfg

      • nvdata

      • nvram

      • md1img_a

    Danger

    Critical: Verify preloader is unchecked. Flashing wrong preloader will brick your device.

  3. Verify file paths:

    • Click each checked partition

    • Confirm path points to correct .img file from F30 package

  4. Flash partitions:

    • Click Download button

    • Power off device

    • Hold Back button (top right)

    • While holding, plug in USB cable

    • SP Flash Tool will auto-detect and flash

    • Wait for green “Download OK” checkmark

    • Disconnect USB

Step 4: Restore Identifiers with SN Write Tool

  1. Launch SN Write Tool:

    • Run SN_Writer.exe as Administrator

  2. Configure settings:

    • Click System Config

    • In Write Option, check only:

      • ☑ IMEI

      • ☑ BT Address

      • ☑ Wifi Address

    • Under IMEI Option, select Dual IMEI

  3. Load database files:

    • Check “Load AP DB from DUT”

    • Check “Load Modem DB from DUT”

    • Click MD1_DB → Select MDDB_InfoCustomAppSrcP_MT6761... from AP DB Base\MT6761

    • Click AP_DB → Select APDB_MT6761... from same folder

    • Click Save

  4. Write identifiers:

    • Click Start

    • Enter your values from recorded identifiers:

      • IMEI_1: Your original IMEI

      • BT Address: Your Bluetooth MAC

      • Wifi Address: Your Wi-Fi MAC

    • Click OK

  5. Flash identifiers:

    • Power off device

    • Hold Back button

    • While holding, plug in USB cable

    • Wait for green PASS message

    • Disconnect USB

Step 5: Verification

  1. Check identifiers:

    • Power on device

    • Go to Settings → About Phone

    • Verify IMEI and MAC addresses match your recorded values

  2. Verify enabled bands:

    • Dial *#*#3646633#*#* to open Engineer Mode

    • Tap Telephony → Band Mode

    • Confirm LTE bands 2, 4, 12, 13, 17, 66, 71 are enabled

    Warning

    Do not change settings in Engineer Mode unless you know what you’re doing.

  3. Test connectivity:

    • Insert US carrier SIM

    • Enable mobile data in Settings → Network & internet

    • Verify LTE icon appears

    • Make test call and browse web

Troubleshooting

No IMEI or Invalid IMEI

Cause: Step 4 skipped or SN Write Tool failed.

Solution:

  • Repeat Step 4, carefully entering YOUR original IMEI

  • Check IMEI on device box or under battery (if accessible)

Signal Shows But No Network Connection

Cause: Carrier hasn’t activated IMEI, or weak signal area.

Solution:

  • Contact carrier to refresh IMEI on network

  • Reset network settings: Settings → System → Reset → Reset Wi-Fi, mobile & Bluetooth

SP Flash Tool “PMT Changed” Error

Cause: Scatter file partition layout mismatch.

Solution:

  • Verify using scatter file from F30 US Bands Package

  • Confirm F21 Pro is 4GB/64GB variant

SP Flash Tool Doesn’t Detect Device

Cause: Drivers not installed or incorrect button timing.

Solution:

  • Verify MediaTek VCOM drivers in Device Manager

  • Use USB 2.0 port instead of USB 3.0

  • Confirm holding Back button (top right) while plugging in

  • Try different USB cable

Weak Signal After Modification

Cause: Expected hardware limitation—antenna design not optimized for US frequencies.

Solution:

  • Normal behavior for bands 12, 13, 17, 71

  • Performance better on bands 2, 4, 66

  • Consider carrier using bands 2/4 primarily (T-Mobile urban areas)

  • No software fix available

Reverting to Chinese Bands

  1. Restore NV partitions:

    python mtk w nvram,nvdata,nvcfg nvram_backup.bin,nvdata_backup.bin,nvcfg_backup.bin

  2. Flash stock Chinese modem with SP Flash Tool

  3. Original identifiers restore automatically from backup