Due to defective controller of the video glasses, there is no audio when watching a video on the video glasses. There is only sound when the controller is switched off which could mean a short-circuit inside the controller audio wirings.

So the composite video source and audio source are directly connected to the video glasses using the supplied "Signal-connect line 2" cable. Audio was audible from the earphones plugged into the audio jack of the video glasses. Since there is no power supply to the video glasses, there is no video.

This narrows down the problem to the controller.

[The controller is the device that contains the lithium battery. It combines power source from battery, video & audio signals to the video glasses. GX-380 model's controller has no audio volume / video brightness controls on it.]