BLH7840 is a FT230X chip based USB <--> serial converter. It is used to connect the Blade 350QX to computer to update firmware and if firmware version 3 is flashed to connect it to GUI for diagnosis. The GUI can be downloaded here: https://www.horizonhobby.com/pdf/350_QX_PC_Interface.zip
If the FT230 driver was installed correctly BLH7840t will appear in the device manager als serial interface once it is connected to USB (no need to connect to Blade at this time).

Here is BLH7840 open:


Remark: Masse means ground.
br HE
If the FT230 driver was installed correctly BLH7840t will appear in the device manager als serial interface once it is connected to USB (no need to connect to Blade at this time).

Here is BLH7840 open:


Remark: Masse means ground.
br HE