Demolition machine cover, left and right sound channel audio output socket without loose, check the wiring welding is good. Trial tweezers separately touch switch integrated circuit XIC3, CIC4 (both for TC4053) 1 foot, found the horn without reaction; Touch again op-amp integrated circuits XIC1, XIC2 buffer (1558) 2, 6 feet, and found that the speaker; Directly from the audio processor XIC6 (KA9401) 30, 35 feet lead to signal into the horn, the sound is normal, on the basis of suspected the mute circuit malfunction. This machine noise circuit as shown in figure 3, in the process of instant on/off or selects a, high level from the CPU via XR39 add to Q6 base, Q6 and Q4 conduction, Q4 collector output of high level Q1 and Q2 conduction, L, R channel signal is short circuit to ground at this time, so as to realize the noise. V7uservice manual download site
 V7uservice manual download site
Examination revealed Q6 base and the collector are in low level. Remove the Q6, measuring its ce knot has short circuit breakdown, after replacement, troubleshooting.V7uservice manual download site