Thanks Paleo12 and Sfar, very much appreciate your help.
The computer and mobile phone connected to the receiver is not a problem now, but I suddenly found that the subwoofer sound is very small, when I use the mobile phone to use the 3.5mm to RCA cable to connect to the receiver to play music or listen to the FM radio, The left and right speakers can hear the bass, but the subwoofer is similar to none, the sound is very weak, I don't know why. Is the subwoofer broken?