-Tested working on firmware A125USQS3BVA2
-A MTK bootloader unlocking tool, tested working with UnlockTool
-This is for A125U on binary 3 ONLY
Special thanks to @Boster27 for translate guide and test method
1- Boot into Download Mode (vol+ & vol- & pwr) and flash this custom BL file BL_A125.tar with ODIN patched using the BL button. The device will reboot to an error screen, this is normal.
2- Boot into BROM mode using Test Points (picture attached, needs light dissasembly). Using UnlockTool or your MTK tool of choice, head to the Samsung section and select A125, then on the BROM tab, choose Unlock Bootloader.
After this the device should reboot into recovery and perform a factory reset automatically. In case it doesn't, go into recovery manually (vol+ & pwr) and perform a factory reset. After this the device should boot normally.
3- Once the setup process is complete, connect to Wifi and enable Developer Options to confirm that OEM Unlock is enabled and unlocked. Install the latest version of Magisk Manager and use it to patch the AP file for the corresponding firmware.
4- Boot into Download Mode, make sure the AutoReboot option is unchecked in ODIN, and flash the magisk_patched.tar AP file, and the stock CP, CSC and USERDATA files. Then manually boot into recovery and perform a factory reset. After this the device should boot normally.
5- Once the setup process is complete again, connect to Wifi and enable Developer Options to confirm that OEM Unlock is still enabled and unlocked. Install the latest Magisk app and launch the app.
It should show a dialog asking for additional setup. Let it do its job and the app will automatically reboot your device.
You write the BL_A125.tar, disconnect the battery and unlock the booloader, after this it enters without problems and is deleted.
If it doesn't, disconnect battery and force enter recovery with volume up and power, do a factory reset