Phone Model

• Galaxy S21 FE 5G ( SM-G991U ) Verizon

• IMEI: 350166284742611 || TAC: 350166 || FAC: 28 || SNR: 474261 || CD: 1

Enter Bootloader

1. With the phone powered off , hold both volume up and volume down until you enter it

   

Enter Recovery Mode

1. Phone has to be connected via usb

2. Power Down Phone

   • Hold power button and volume down until screen goes blank

3. Once screen has gone blank , continue to hold down the power button

4. Release the volume down , wait half a second , switch to volume up

5. Continue to hold volume up and power button until you enter recovery mode

Attempt

• Existing firmware is corrupted somehow

• Lock screen runs separately on an isolated chip

• Normally you could enable “developer options” in android settings

• • And then use android debugging bridge ( adb ) program to upload a new firmware image to the device

  • https://www.sammobile.com/samsung/galaxy-s21/firmware/SM-G991U/VZW/download/G991USQS5CVCB/1629585/

• Since developer options can’t be enabled , there is a failsafe adb command , “sideload” to push a new firmware image

• However this keeps failing no matter which firmware I try

JTAG

• JTAG ( Joint Test Action Group ) = hardware interface that can access internal memory and registers

• https://www.eetimes.com/jtag-101-part-1-overview-and-on-chip-debug-methods/

• I've never done this before , but I imagine a lot of shops have

• But somewhere on the circuit board , there is a place to connect a debugger over the "JTAG" interface

• https://android.stackexchange.com/a/158897

• Then you should be able to extract the data stored in the internal memory.

JTAG Links

• https://android.stackexchange.com/questions/37019/what-is-jtag-in-regards-to-android#37023

• https://www.fonefunshop.com/jtag-emmc-chip-off/Jtag-Adapters/Samsung-Jtag-Adapters/S-Boot-Repair-Clip.html

• https://www.fonefunshop.com/jtag-emmc-chip-off/Jtag-Adapters/Samsung-Jtag-Adapters/gsm-multi-functional-boot-cable.html

• https://www.cellcorner.com/xshp/cell-phone-unlocking/samsung-jtag-adatpers/

• https://android.stackexchange.com/questions/137895/can-fastboot-be-used-to-backup-device

• https://www.ifixit.com/Device/Samsung_Galaxy_S21

• https://naldotech.com/samsung-galaxy-s21-ultra-download-recovery-mode/

• https://openocd.org/pages/supported-jtag-interfaces.html

• https://vrm24.com/reviews/tech-review-of-samsung-galaxy-s21-sm-g991/

• https://www.fonefunshop.com/jtag-emmc-chip-off/Jtag-Boxs/

• https://www.fonefunshop.com/jtag-emmc-chip-off/Jtag-Boxs/GPGJTAG-Box-Jtag-Pro.html

• https://www.fonefunshop.com/jtag-emmc-chip-off/Jtag-Adapters/Samsung-Jtag-Adapters/gsm-multi-functional-boot-cable.html

• https://www.fonefunshop.com/jtag-emmc-chip-off/Jtag-Boxs/emmc-isp-chip-off-forensic-data-extraction-kit.html

• https://www.mobilerdx.com/category/samsung

• https://www.fonefunshop.com/jtag-emmc-chip-off/Jtag-Adapters/Samsung-Jtag-Adapters/

• https://www.mobilerdx.com/2020/08/latest-easy-jtag-plus-box-setup.html

• https://medusabox.com/eng/features/models

• https://www.fonefunshop.com/jtag-emmc-chip-off/Jtag-Adapters/medusa-box-2-basic

• https://www.mobilerdx.com/2017/07/z3x-box-and-lg-tool-latest-setup-download.html

Boot Repair Service

• https://www.fonefunshop.com/phone-repair-service/phone-jtag-boot-repair-service/Samsung-Boot-and-Software-Repair-Service-mail-in-repair-service.html

  • Newer phones not supported

Samsung Galaxy S21 UltraUFS ISP Pinout Image

1. You need to take the rear case away from your phone. Next, unplug the motherboard from the existing battery, fingerprint sensor, and camera.

2. Unscrew the screws from the motherboard and take it out and put it in a safe place.

3. On your motherboard, locate the six eMMC pins. The pins are TxOp, TxOn, RxOp, RxOn. You will require to cut through the steel cover to reveal them.

4. Bring the UFI box and take the adapter out from it. You will see the exact same pins in the adapter I have mentioned in the previous step.

5. Solder the 4 pins: TxOp, TxOn, RxOp, RxOn with jumpers between the motherboard and the adapter. Left the VCC and VCCQ for the USB to power them out.

6. Put the adapter inside the UFI box. Connect the box to the computer.

7. Connect the motherboard to the phone’s battery. Then, put the USB cable on the phone and connect it to the computer.

Universal JTAG Interface

• https://www.fonefunshop.com/jtag-emmc-chip-off/Jtag-Adapters/universal-jtag-interface

Misc

• https://www.mobilerdx.com/2018/11/umt-dongle-samsung-tool.html