If your flight controller gets bricked, it'll not be able to power up properly. In this case, flash firmware in DFU mode is needed. There are two ways to flash firmware in DFU mode, via the SpeedyBee app or in your PC Betaflight configurator.

Method 1 Flash a bricked flight controller in the PC Betaflight configurator

1.Hold down the BOOT button, then insert the USB cable to enter DFU mode.

2. The flight controller status changes to solid red light, and the blue light is off.

3. Enter Betaflight, the serial port changes to DFU, click to update firmware.

4. After selecting the flight controller version based on your own flight controller, choose to load the firmware from the internet

（If you are flashing firmware version 4.4 or above, you can refer to this article：How to correctly flash Betaflight 4.4 firmware.）

5.After the loading is complete, click to flash the firmware

6.After the flashing is complete, you can click to connect and enter normally

4.You may use the ImpurseRC driver fixer to fix this issue. Please refer to:

What If your Flight Controller Won't Enter the DFU Mode（Windows）?

Method 2 Flash a bricked flight controller in the SpeedyBee app

If your flight controller has built-in Bluetooth & WiFi chip(for example SpeedyBee F7 V2/F7 V3/F745 BLS 35A AIO), then you could flash the bricked flight controller in the SpeedyBee app.

Here are the steps:
1. Connect a USB cable to a phone charger.
2. Hold the BOOT button (usually the only button on the FC) with one hand, plug the USB cable into the FC with the other hand at the same time, then the FC will enter DFU mode.
3. Open the SpeedyBee app, go to the FC Firmware Flasher page, and perform the Firmware Flashing as prompted. We recommend you enable "Full Chip Erase".

4. After the firmware is flashed successfully, connect to the app immediately. Then the app will ask you to apply custom default settings. Answer 'Apply'.