For users of Redmi K90, restoring to the initial version (i.e., downgrading the system or reverting to the factory-installed system) is a common requirement to address system lag, compatibility issues, or to access the functions of the older version. This article will provide detailed explanations of three scientific and safe operation methods, covering the system rollback needs in different scenarios.
I. Reset to Factory Settings: Applicable to regular scenarios where the BL lock has not been unlocked.
If the Bootloader (BL lock) of the mobile phone is not unlocked and the target version is only slightly different from the current version, a basic rollback can be achieved by restoring the factory settings. This method is simple to operate, but please note the following steps:
Data backup: Through “Settings – My Device – Backup and Restore”, contact information, photos, documents, etc. can be backed up to Xiaomi Cloud or a computer. If the phone has an SD card inserted, it is necessary to remove it in advance to avoid accidental deletion.
2. Enter Recovery Mode: After powering off the device, press and hold the “volume down + power button” for 10 seconds. Wait for the phone to vibrate and then release the button. This will bring you to the Fastboot interface. Use the volume keys to select “Recovery Mode”, and after entering, choose “Clear Data – Factory Reset”.
3. Wait for the system rollback: The phone will automatically delete the current system and install the factory-installed version. The entire process takes approximately 15 minutes. After the restoration is complete, you will need to reconfigure basic settings such as language and Wi-Fi.
Notes: This method is only applicable for version rollbacks within the same major version (e.g., reverting from MIUI 15.0.1 to 15.0.0). If you attempt a cross-version operation (such as reverting from MIUI 15 to MIUI 14), it may result in the system not starting.
II. Manual Replacement of System Packages: Suitable for precise downgrade when BL lock has been unlocked
For users who have unlocked the BL lock, they can achieve precise downgrade by replacing the system update package. This method requires downloading the target version package and manually triggering the installation:
Download the target version package: Obtain the old version system package that matches the Redmi K90 from the official Xiaomi community or a third-party ROM site (make sure the version number is compatible with the hardware).
2. Rename and Replace: Rename the downloaded ZIP file to “download_rom.zip” and then move it to the “/download_rom” directory on the phone.
3. Trigger system verification: Go to “Settings – My Device – MIUI Version”, click the upper right menu and select “Manually Select Installation Package”. The system will automatically verify and install the previous version.
4. Clear data and restart: After installation, in the Recovery mode, select “Clear data” to avoid system abnormalities caused by cache conflicts.
Risk Warning: If the replacement process is interrupted or the package name is incorrect, it may cause the device to brick. It is recommended to keep the phone’s battery level above 50% throughout the process and turn off the “System Automatic Update” function before operating.
III. Retracing of the Line Brush Tool: The Ultimate Solution
When the above methods fail, the wire brush is the ultimate solution to restore to the original version. This method requires unlocking the BL lock and using professional tools. The operation steps are as follows:
Unlock BL lock: Apply for unlocking permission through the official website of Xiaomi Unlock Tool. After waiting for the 72-hour review period, connect the computer in Fastboot mode to perform the unlocking process.
2. Enter EDL mode: After powering off, press and hold the “volume down + power button” to enter Fastboot mode. Then, use the data cable to short-circuit the test points to trigger the EDL (Emergency Download Mode).
3. Flashing the old version: Open the official Xiaomi flashing tool (MiFlash), select the path of the line flashing package that matches the Redmi K90, click “Refresh” to identify the device, and then proceed with the flashing process. The entire process takes approximately 5 minutes.
4. Initial Setup: After the device is flashed, it will automatically restart to the initial settings interface. You will need to reconfigure the language, Wi-Fi, and other parameters.
Technical requirements: The line brush operation requires entering the EDL mode and involves hardware short-circuiting. For beginners, it is recommended to seek assistance from Xiaomi’s after-sales service or professional repair shops to complete the operation.
Key Considerations:
Data Security: Before any operation, make sure to back up the data to prevent data loss due to system rollback.
2. Version Compatibility: Downgrading across major version numbers may cause system instability. It is recommended to preferentially choose the official recommended rollback version.
3. Battery Assurance: During the operation, ensure that the phone has sufficient battery power (it is recommended to keep it above 50%). Avoid interrupting the flashing process due to low battery levels.
4. Disable the “Find My Phone” function: If the “Find My Phone” feature is enabled, you need to log in to your Xiaomi account before using it to turn it off. Otherwise, after the device is restored, it may trigger the activation lock.
By using the above methods, users of Redmi K90 can choose the appropriate system rollback solution according to their own needs. If there are any doubts about the operation steps, it is recommended to refer to the official Xiaomi documentation or contact customer service for technical support.