Defective controller. When controller is switched on, video glasses show video image but there is no audio output from either controller audio jack or video glasses' audio jack.
When controller is switched off, there is audio output from the audio jack of the controller but is only audible from amplified speakers (sound volume might be to low for earphones). There is no sound volume / video brightness controls on controller of GX-380 model.
So there might have been a short circuit in the audio wirings inside the controller. Or could it be the factory adjusted sound volume is too low or muted?