Connected the fan at the point of supply 3.3 V (pins 20\40). The speed of the fan is sufficient to provide acceptable temperature level (fan at 5 V). When you turn off VIM this connector is also switched off (and the fan also turns off). So the fan turns on when you turn on VIM and is completely off when shutting down (the power supply is plugged in). Request to the Khadas representatives - add documentation description connector (pinout diagram) allowable current for all of the supply pins (5 V and 3.3 V) and specify which contacts have a constant voltage (and off) and which are disabled when you turn off VIM (when the power supply to the network).