By the failure phenomenon analysis, failure should be in the playback of audio circuit. Try in video reproduction state, from audio playback process integration block IC401 (XRA7767A) 7, 8, 9 feet into the induction signal, the speaker inside have "hum hum". Illustrate IC401 audio signal processing and the audio input after all work is normal, fault should be in audio head to IC401 audio input circuit or super audio signal generator. Try to determine the scope of the fault, in the condition of video reproduction, use a screwdriver to touch head (audio heads) output signal, the results remain silent in the young voice, specify in the former. Ultimately, finally had external audio signal input capacitance is IC4014 foot C413 (47 (including 35 v/F) serious leakage. After replacing C413 fault disappear.n9mservice manual download site