How to Flash LineageOS 14.1 on Lenovo S850: A Comprehensive Guide

Upgrading your aging Lenovo S850 can breathe new life into it, and one of the best ways to do this is by flashing a custom ROM. LineageOS 14.1, based on Android 7.1.2 Nougat, offers a significant improvement over the stock firmware, providing enhanced features, performance, and customization options. This guide provides a detailed walkthrough on how to flash LineageOS 14.1 onto your Lenovo S850. Please proceed with caution and ensure you understand the risks involved.

Before we begin, it’s crucial to understand that flashing a custom ROM is not without risk. Incorrect procedures can potentially brick your device, leading to it becoming unusable. Ensure you read through this guide carefully and follow each step precisely. We are not responsible for any damage caused to your device during this process.

Prerequisites and Important Considerations

Before you start the flashing process, ensure you meet the following requirements:

Backup Your Data: This process will wipe all data from your phone. Back up all important data, including contacts, messages, photos, and files, to your computer or cloud storage.
Battery Level: Ensure your Lenovo S850 has at least 50% battery charge to prevent interruptions during the flashing process.
ROW Firmware: Your Lenovo A850 must be running on ROW (Rest of World) firmware. You can check this in “Settings” -> “About phone” -> “Baseband version”. It should contain “ROW”. If you are on CN firmware, you need to flash a ROW ROM first. A suitable ROW ROM can be found here.
TWRP Recovery: You need to have TWRP (Team Win Recovery Project) custom recovery installed on your Lenovo S850. If you don’t have it, you’ll need to flash it first.
Download Necessary Files: Download the LineageOS 14.1 ROM zip file and store it on your phone’s SD card. You can download the ROM from here.

Step-by-Step Guide to Flash LineageOS 14.1 on Lenovo S850

Once you have met all the prerequisites, follow these steps to flash LineageOS 14.1 on your Lenovo S850:

Boot into TWRP Recovery:
- Power off your Lenovo S850 completely.
- Press and hold the Volume Up button and Power button simultaneously until the TWRP recovery menu appears. You may need to try different combinations or methods if this doesn’t work initially. If you encounter issues booting into recovery using buttons, you can try booting through the power menu after enabling “Advanced reboot” in Developer Options (Settings -> About phone -> tap “Build number” multiple times -> Developer Options -> Advanced reboot).
Perform a Nandroid Backup (Highly Recommended):
- In TWRP Recovery, navigate to “Backup”.
- Select all partitions (System, Data, Boot, etc.) to backup.
- Swipe to backup. This creates a full backup of your current ROM, allowing you to restore your phone to its previous state if anything goes wrong.
Wipe Data/Factory Reset:
- In TWRP Recovery, navigate to “Wipe”.
- Select “Advanced Wipe”.
- Check “Dalvik / ART Cache”, “System”, “Cache”, and “Data”.
- Swipe to wipe. This will erase your current system and data partitions, preparing your phone for the new ROM.
Flash the LineageOS 14.1 ROM:
- In TWRP Recovery, navigate to “Install”.
- Locate the LineageOS 14.1 ROM zip file that you downloaded and placed on your SD card.
- Select the zip file and swipe to flash. The installation process may take a considerable amount of time, so be patient and do not interrupt it.
Reboot System:
- Once the flashing process is complete, tap on “Reboot System”.
- The first boot after flashing a custom ROM may take longer than usual. Be patient and wait for your phone to boot into LineageOS 14.1.

Successful flash of LineageOS 14.1 on Lenovo A850, showcasing the Android 7.1.2 interface.

Post-Installation Steps and Important Fixes

After successfully booting into LineageOS 14.1, you may need to perform some additional steps:

Enable Root Access and Advanced Reboot:
- Go to “Settings” -> “About phone”.
- Tap “Build number” multiple times to unlock “Developer options”.
- Go back to “Settings” and enter “Developer options”.
- Enable “Advanced reboot” and configure “Root access” as desired.
Fixing IMEI Issues:
Flashing custom ROMs can sometimes lead to IMEI (International Mobile Equipment Identity) issues, causing problems with mobile network connectivity. If you encounter IMEI problems, you can try the following methods to fix them:
- Using Tool Hero: Tool Hero is an updated version of MobileUncle Tools and can be used to restore IMEI. After using it, you can uninstall the app.
- Using MobileUncle Tools: Follow the steps outlined in this XDA thread to use MobileUncle Tools for IMEI repair.
- IMEI & SN Writer Tool: For a more advanced method, you can use the IMEI&SN Writer V1.5.3 tool. You might need to flash the ROW ROM (provided here again for convenience) and install necessary drivers before using this tool. Format your phone using Flash Tool (Format -> Auto) and then flash the ROW ROM again (Download). After this, use IMEI&SN Writer V1.5.3 to restore your IMEI.

Known Bugs and Potential Issues

While LineageOS 14.1 significantly improves your Lenovo S850 experience, be aware of the following known bugs and issues:

Camera Focus: Camera focus might be buggy and may not work correctly.
Limited System Space for Gapps: There is limited system space, which might prevent installing Gapps (Google Apps) directly. A workaround is to move WebView to a user app and then install a minimal Gapps package like Pico Gapps.
Magisk/SuperSu Installation Issues: Installing Magisk or SuperSu for root management might not work.
Xposed Libraries: Xposed libraries are untested and might cause issues.
Recovery Boot Issues: Getting into recovery using hardware buttons might be inconsistent. Use the “Advanced reboot” option from Developer Options as a reliable alternative.
Reboot from Recovery Issue: Rebooting to system from recovery might cause the phone to power off. If this happens, unplug and re-plug the battery and reboot.
Reboot Powers Down Device: The “Reboot” option might simply power down the device instead of rebooting.
Potential Bootloops with Greenify: Using Greenify app might cause bootloops.
Mobile Data Instability: Some users have reported mobile data problems where data connectivity is intermittent.

Conclusion

Flashing LineageOS 14.1 on your Lenovo S850 can give your device a new lease of life with Android 7.1.2. While there are some bugs and potential issues, the improved performance and features might be worth the effort for experienced users. Remember to proceed with caution, back up your data, and follow the instructions carefully. If you encounter any problems, refer to the troubleshooting steps and online communities for assistance.

Disclaimer: Flashing custom ROMs involves risks. Proceed at your own risk. We are not responsible for any damage to your device.

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