What Is ISP Pinout

ISP (In-System Programming) pinout is a hardware-level technique that allows a repair technician to communicate directly with the NAND flash storage on the Samsung SM-A426U motherboard without relying on the device's operating system or bootloader. By identifying and connecting to specific test pads on the PCB, a compatible ISP tool can read, write, or erase data at the chip level. This method is especially valuable when normal USB-based flashing is not possible due to software corruption, bootloader failure, or an active FRP (Factory Reset Protection) lock that blocks standard OEM unlock paths.

When to Use ISP

ISP access is the preferred repair method for the SM-A426U in the following scenarios:

  • FRP / Google Account Lock: When the device is stuck on the Google verification screen and ADB or download mode are inaccessible.
  • Dead Boot / Brick: When the phone shows no signs of life after a failed firmware flash or interrupted OTA update.
  • Bootloader Corruption: When the bootloader partition is damaged and the device cannot enter EDL or download mode normally.
  • Persistent Boot Loop: When software-based repair tools fail to resolve a recurring restart cycle.
  • IMEI / EFS Restore: When the EFS partition needs to be read or restored after a baseband failure.

SM-A426U ISP Test Points

The SM-A426U uses a UFS 2.1 storage interface routed to dedicated test pads on the motherboard. The standard ISP signals for UFS-based Samsung devices are listed below. Note that exact pad coordinates on this specific board revision are not fully verified in public documentation and are marked accordingly.

  • CLK (RCLK): UFS reference clock signal pad
  • DATA0 (DIN / DOUT): Differential data line pad (positive)
  • DATA0N: Differential data line pad (negative)
  • VCC: 2.9V main storage power supply pad
  • VCCQ: 1.8V I/O voltage pad
  • GND: Ground reference pad
  • RST: Reset signal pad (device-specific; location uncertain)

Always verify pad locations against a confirmed board-level schematic or a trusted ISP pinout diagram before making contact.

ISP Access Procedure

Follow these steps to establish a successful ISP connection on the SM-A426U:

  • Fully disassemble the device and remove the motherboard from the chassis.
  • Identify the UFS ISP test pads using a verified pinout diagram for the SM-A426U.
  • Solder fine ISP wires or apply ISP probe clips to CLK, DATA0, DATA0N, VCC, VCCQ, and GND pads.
  • Connect the wired pads to your ISP tool interface box (e.g., EasyJTAG Plus or UMT ISP adapter).
  • Launch the corresponding ISP software, select the Snapdragon 750G / SM-A426U profile, and apply the correct voltage settings before powering on.
  • Execute the required operation (FRP erase, firmware write, or EFS backup) and safely disconnect after the tool confirms completion.

Safety Tips and Precautions

ISP work carries significant risk if performed incorrectly. Observe the following precautions at all times:

  • Always verify VCCQ is set to 1.8V and VCC to 2.9V — incorrect voltages will permanently damage the UFS chip.
  • Remove the battery and all external power before soldering to test pads.
  • Use a temperature-controlled soldering iron at no more than 300°C and fine-gauge wire (30 AWG or thinner).
  • Double-check all pad connections for shorts with a multimeter before applying power.
  • Work in an ESD-safe environment and wear an anti-static wrist strap throughout the procedure.
  • Never force a flash if the tool does not detect the chip — recheck connections before retrying.

Pin / Test Point Reference

PinDescription
CLK (RCLK)UFS reference clock signal test pad — Exact pad location unconfirmed; verify against schematic
DAT0+UFS differential data line, positive — Exact pad location unconfirmed
DAT0-UFS differential data line, negative — Exact pad location unconfirmed
VCCMain UFS storage supply voltage — 2.9V
VCCQUFS I/O voltage — 1.8V
GNDGround reference pad
RSTUFS reset signal pad — Location uncertain on SM-A426U board revision

Tools required: EasyJTAG Plus with UFS ISP adapter, UMT (Ultimate Multi Tool) with ISP cable set, Octoplus / Octopus Box with ISP support, 30 AWG ISP wire or ISP probe clip set, Temperature-controlled soldering station, Digital multimeter (for continuity and short checks), Anti-static wrist strap and ESD mat

Supported operations: FRP Erase, Dead Boot Repair, Read Firmware / Full UFS Dump, Write Firmware, EFS Backup and Restore, IMEI Repair (via EFS restore)

âš  Safety note: UFS VCC must be 2.9V; VCCQ must be 1.8V. Incorrect voltage permanently destroys the storage chip. Disconnect battery before soldering. Work in an ESD-safe environment.