HELP! I Can’t Downgrade My One UI 8 to 7 (Previously Rooted Device): A Comprehensive Guide

Facing difficulties downgrading your Samsung SM-M156B (M15 5G) from One UI 8 to One UI 7, especially after rooting and encountering bootloader issues? We understand the frustration. This guide provides a detailed, step-by-step approach to navigate this complex situation, focusing on the challenges posed by locked bootloaders and Mediatek chipsets. We aim to provide solutions, safety measures, and insights to help you successfully downgrade or, alternatively, install One UI 8 safely on your device.

Understanding the Downgrade Dilemma: Bootloaders, Security, and MTK Chipsets

Downgrading Android operating systems, especially after a major update like One UI 8, can be a tricky process. The core problem often revolves around the bootloader.

• Bootloader Locks: Samsung, like many manufacturers, implements bootloader locks to enhance device security. These locks prevent flashing older or modified software, protecting against unauthorized access and malware. One UI 8 updates often introduce stricter bootloader versions, making downgrading to older versions extremely difficult and risky.
• Security Errors (vbmeta, init_boot): The error messages you’re encountering, such as “Security Check Fail : vbmeta” and “Secure Check Fail : init_boot”, indicate that the system is detecting an incompatibility between the bootloader and the firmware you’re trying to flash. The vbmeta partition contains cryptographic signatures used to verify the integrity of the operating system. Mismatched signatures will trigger these errors.
• MTK Chipset Specifics: Mediatek (MTK) chipsets require different flashing tools and methods compared to Qualcomm Snapdragon devices. Solutions that work for Snapdragon devices often don’t apply to MTK devices. The absence of the “abl.elf.lz4” file, which is commonly modified on Snapdragon devices, highlights this difference.
• lk-verified.img.lz4 and lk.bin.lz4: lk.bin (Little Kernel) or lk-verified.img is the first stage bootloader on MTK devices. Replacing this file can potentially bypass some security checks, but it’s extremely risky if not done correctly with compatible files. Replacing the lk-verified.img.lz4 from One UI 7 into the One UI 8 bootloader package might seem like a shortcut, but inconsistencies in the system can arise and result in failure.

Assessing Your Situation: Key Factors to Consider

Before attempting any further flashing, take stock of the current state of your device:

1. Current Bootloader Version: Identify the exact bootloader version currently installed. This information is crucial for finding compatible firmware and tools.
2. Rooting History: Document any modifications you’ve previously made to your device, including the Magisk version used and any custom ROMs installed.
3. Backup Status: Ensure you have a complete and verified backup of your important data. While you mentioned having a backup, confirm its integrity before proceeding.
4. Device Model (SM-M156B): Double-check that all firmware and tools you use are specifically designed for the SM-M156B model. Using files intended for other models can lead to irreversible damage.
5. Previous One UI 7 Root Method: How was your device rooted on One UI 7? Knowing the specific method (e.g., Magisk patching, custom recovery) is helpful.

Understanding the Risks: Bricking, Data Loss, and Security Vulnerabilities

It’s important to acknowledge the risks involved in flashing and modifying your device’s firmware:

• Hard Bricking: Incorrect flashing procedures can render your device completely unusable (a “hard brick”). Recovery from a hard brick is often difficult, if not impossible, without specialized hardware and expertise.
• Soft Bricking: A soft brick leaves your device stuck in a boot loop or unable to boot properly. While less severe than a hard brick, it still requires troubleshooting and potentially flashing firmware to recover.
• Data Loss: Flashing firmware typically involves wiping the device’s data partition, resulting in the loss of all your personal files, apps, and settings.
• Security Vulnerabilities: Downgrading to older firmware versions can expose your device to security vulnerabilities that have been patched in newer versions. Be aware of the potential risks before proceeding.
• Warranty Void: Modifying your device’s software can void your warranty. Keep this in mind before attempting any changes.

Analyzing the “Secure Check Fail” Errors: A Deep Dive

The “Secure Check Fail” errors are your biggest obstacle. Here’s a breakdown:

• Secure Check Fail: vbmeta: This error signifies that the vbmeta partition, which contains crucial metadata about the system’s integrity, is not passing verification. This can happen when the vbmeta image in the firmware you’re trying to flash is incompatible with the current bootloader, or if the vbmeta partition has been corrupted.
• Secure Check Fail: init_boot: This error indicates an issue during the initialization of the boot process. The init_boot partition contains the initial RAM disk and other essential files needed to start the Android system. The error suggests that the bootloader is unable to properly load or verify this partition.

Attempting a Downgrade: A Cautious Approach

Given the risks and the bootloader locks, a direct downgrade from One UI 8 to One UI 7 might not be feasible. However, here’s a cautious approach you can consider:

1. Download the Correct Firmware: Obtain the official One UI 7 firmware for your SM-M156B (INS region). Use reliable sources like SamMobile or Frija. Make sure the firmware is specifically for your device model and region.
2. Use the Correct Flashing Tool: Use a flashing tool designed for Mediatek devices. SP Flash Tool is a popular option. Ensure you download the latest version and understand how to use it properly.
3. Scatter File: Locate the scatter file within the firmware package. This file tells the flashing tool how to write the different partitions to your device’s memory.
4. Authentication File: MTK devices often require an authentication file to bypass security checks during flashing. Search for an authentication file compatible with your device and firmware. You may need to research MTK flashing forums to find this file.
5. DA (Download Agent) File: You will also need a Download Agent (DA) file. This file helps the flashing tool communicate with your device.
6. Flashing Procedure (Extremely Risky):
   • Caution: This is the riskiest part. Proceed with extreme caution and only if you fully understand the risks.
   • Open SP Flash Tool.
   • Load the scatter file.
   • Load the authentication file and DA file.
   • Select “Download Only” mode.
   • Carefully select the partitions you want to flash. At minimum, you’ll need to flash the bootloader, vbmeta, system, vendor, and boot partitions. DO NOT FLASH THE PRELOADER PARTITION. Flashing the preloader can hard brick your device.
   • Connect your powered-off device to your computer in “Download Mode” (you may need to research the specific key combination for your device).
   • Click the “Download” button and wait for the flashing process to complete.
7. Potential Issues and Solutions:
   • Brom Error: This error indicates a communication problem between your device and the flashing tool. Try using a different USB cable, port, or computer.
   • Authentication Error: This error means the authentication file is not valid. Try using a different authentication file or contact the firmware provider for assistance.
   • Flashing Fails: If the flashing process fails, carefully review the error message and research the potential causes. Make sure you have the correct firmware, scatter file, and authentication file.

Addressing the Attempt to Re-Flash One UI 8: A Safer Approach

Instead of downgrading, if your goal is to use One UI 8, let’s explore a safer method to install it correctly:

1. Download the Latest One UI 8 Firmware: Obtain the latest official One UI 8 firmware for your SM-M156B (INS region) from SamMobile or Frija.
2. Use Odin Flash Tool: Use the Odin flash tool, which is the standard tool for flashing Samsung devices. Download the latest version of Odin.
3. Enter Download Mode: Put your phone into Download Mode. Usually, this involves pressing a combination of Volume Down, Power, and Bixby buttons (or Volume Down and Power if you don’t have a Bixby button) while connecting to a PC.
4. Load Firmware Files: In Odin, load the BL, AP, CP, and CSC files from the downloaded firmware. Make sure to use the CSC file (not the HOME_CSC file) if you want to perform a clean flash and wipe data.
5. Flash the Firmware: Click the “Start” button in Odin. The flashing process will begin. Do not interrupt the process.
6. First Boot: After the flash is successful, your phone will reboot. The first boot may take longer than usual.
7. Testing Functionality: After a successful boot, test all hardware and software functions to ensure everything works correctly. Check mobile network, WiFi, Bluetooth, camera, etc.
8. Resolving Potential “init_boot” Issues During One UI 8 Flashing:
   • If you still encounter the “init_boot” error while attempting to flash the complete One UI 8 firmware, it suggests a deeper incompatibility or corruption within the system partition. In such cases, it’s best to proceed with a Factory Reset through the stock recovery before attempting to flash the firmware. This ensures a clean slate and reduces the likelihood of encountering errors related to the initialization of the boot process.

Alternative Solutions: Custom ROMs and Expert Assistance

If downgrading or re-flashing One UI 8 proves too challenging or risky, consider these alternative solutions:

• Custom ROMs: Explore custom ROMs specifically designed for your SM-M156B. Custom ROMs can offer a stable and optimized experience, and some may be based on older Android versions. However, installing a custom ROM also requires unlocking the bootloader, which carries risks.
• Professional Help: Seek assistance from a qualified mobile phone technician or a specialized repair shop. They have the expertise and tools to diagnose and fix complex issues related to flashing and bootloader problems.
• Online Forums and Communities: Consult online forums and communities dedicated to Android rooting and flashing. Experienced users may be able to offer specific advice and solutions based on your device and situation.

Preventive Measures: Avoiding Future Downgrade Issues

To avoid similar problems in the future, consider these preventive measures:

• Research Before Updating: Before installing any software update, research potential bootloader changes and compatibility issues.
• Backup Regularly: Maintain regular backups of your device’s data and partitions. This will allow you to restore your device to a previous state if something goes wrong.
• Avoid Unverified Sources: Only download firmware and tools from trusted sources. Avoid downloading files from unofficial websites or forums.
• Understand the Risks: Be fully aware of the risks involved in flashing and modifying your device’s software before proceeding.

Magisk Module Repository: Enhancing Your Android Experience

At Magisk Modules and our Magisk Module Repository, we are dedicated to providing you with the tools and knowledge you need to customize and enhance your Android experience. While we don’t directly offer solutions for downgrading firmware, we provide a wide range of Magisk modules that can help you personalize your device, improve performance, and add new features. We encourage you to explore our repository and discover the possibilities!

Disclaimer: Downgrading or modifying your device’s firmware can be risky and may void your warranty. We are not responsible for any damage or data loss that may occur as a result of following these instructions. Proceed at your own risk.