RK3399FanControl
From FriendlyELEC WiKi
Change the behavior of the PWM fan
By default, the speed of the fan is dynamically adjusted according to the CPU temperature. If you need to let the fan run, you can modify the script /usr/bin/start-rk3399-pwm-fan.sh to the following:
#!/bin/bash echo 0 > /sys/class/pwm/pwmchip1/export sleep 1 echo 0 > /sys/class/pwm/pwmchip1/pwm0/enable echo 50000 > /sys/class/pwm/pwmchip1/pwm0/period echo 1 > /sys/class/pwm/pwmchip1/pwm0/enable echo 45000 > /sys/class/pwm/pwmchip1/pwm0/duty_cycle