The preliminary judgment for the audio circuit fault phenomenon has a problem, use "fault locating device" check test, found that the machine's sound circuit BA7751 {16} feet no audio output, but the first {7}, {9} feet are normal audio signal, and potential multimeter is used to inspect the integrated circuit of each foot are normal, so decided to IC402 (BA7751) internal circuit has local damage, because the IC is not easy to purchase and the price is expensive, so take the local emergency substitution method, only with a piece of ordinary and cheap audio power amplifier IC LA4140 and two C1815 triode and a number of rc components to repair it, play the effect is very good also. See attached figure after transforming circuit. wjQservice manual download site
 wjQservice manual download site
 wjQservice manual download site
Note: 1. The "x" should be cut off with the original circuit connection. wjQservice manual download site
2. + 5 v, + 12 v voltage from the unit.wjQservice manual download site