Flashing a Control Board (SD Recovery)

When (and why) you flash a control board

Reflashing the control board (CB) reinstalls the miner's operating firmware. It's a SOFTWARE restore - not board repair.

• The web UI won't boot, the miner is stuck in a boot loop, or firmware is corrupted.
• The web UI won't accept a normal firmware upgrade.
• You're moving between signed stock and custom firmware (Braiins/Vnish/LuxOS).
• Recovery from checksum errors (Whatsminer codes 800/801/802/100001+).

Make the SD card correctly

1. Use a SMALL, name-brand microSD: 2-16 GB (SanDisk/Samsung/Kingston). Cards >32 GB frequently fail - the bootloader can't read exFAT/SDXC.
2. Format the card FAT32.
3. Download the correct recovery image for the EXACT model from the manufacturer.
4. UNZIP the image and copy its CONTENTS onto the card (don't just drop the .zip on it).
5. Tools: balenaEtcher (easiest, cross-platform), Win32DiskImager, or Rufus (Windows).

Antminer SD recovery procedure

1. Power OFF the miner.
2. Insert the prepared microSD into the control board's card slot.
3. Power ON - the board auto-loads from the card (~30 s to a few minutes).
4. When the green LED goes STEADY, flashing is complete. Do NOT interrupt power.
5. Power off, REMOVE the card, power on - it boots the recovered firmware.
6. Reconfigure network + pools (config was wiped) and verify the version.

Whatsminer & Avalon

• Whatsminer: flash the control board from a prepared SD card, then FINISH the process with WhatsMinerTool. Used for checksum/signature errors.
• Match the firmware GENERATION (Whatsminer code 8410 = wrong-gen image, e.g. M2x firmware on an M3x).
• Avalon: recovery is done through the AvalonMiner control/upgrade tools; keep the exact-model image.

Newer Antminer locks (2024+ hardware)

The classic 'flash a stock SD image to recover it' no longer works on the newest Antminers - know this before you condemn a locked unit to RMA.

• Amlogic control boards (roughly March 2024+ hardware) block unsigned/custom firmware - a plain SD image won't take.
• Stock firmware from around September 2025 won't boot or downgrade from an SD card and closes the old microUSB unlock path.
• A locked S21 that refuses SD recovery isn't necessarily dead - it may need a controller unlock/downgrade, not a wrongful RMA.
• This is hardware- and firmware-version dependent and moving fast - check the exact board and firmware date before assuming a method works.

The golden rules

• Always use the image for the EXACT model - a wrong image can brick the unit.
• Stable power for the whole flash; use a rack you can't accidentally kill.
• If a correct reflash STILL won't boot the CB -> swap/RMA the unit. That's the end of the field line.