https://devzone.nordicsemi.com/f/nordic-q-a/94565/dfu-firmware-update-issue-with-custom-nrf-52833-boardHi Nordic, Soft device is s140 SDK version is: nRF5_SDK_17.1.0_ddde560 Bootloader - Secure bootloader. We are trying buttonless DFU process using secure bootloader with customized nrf52833 board. When we tried with nrf52833 DK the DFU processen-USTelligent Community 13Wed, 07 Dec 2022 11:17:43 GMThttps://devzone.nordicsemi.com/thread/399383?ContentTypeID=1Wed, 07 Dec 2022 11:17:43 GMT137ad170-7792-4731-bb38-c0d22fbe4515:7da3baeb-2945-454a-9b38-bd5940fba62cHung Bui<p>Hi Hareesh,&nbsp;</p> <p>Error 133 is a generic error and not much we can tell from the error. We may need more debug information from the nRF52.&nbsp;What I can see is that the error occurred right at the time the phone try to connect to the bootloader after it sent the command to switch to bootloader to the application. There is a chance that it couldn&#39;t established the connection to the bootloader.&nbsp;</p> <p><br />If you test by only flash bootloader + softdevice can you do DFU update ?&nbsp;<br /><br />Do you have any bonding on the phone to the nRF52 ?&nbsp;</p> <p></p> <p>I don&#39;t see any reason it wouldn&#39;t work on your custom board.&nbsp;I don&#39;t know if you use 32kHz crystal or 32kHz RC on the board but I assume you have configured the bootloader accordingly.&nbsp;</p><div style="clear:both;"></div>