From the phenomenon analysis, data, audio circuit, field scanning circuit may cause the failure. m4jservice manual download site
 m4jservice manual download site
Test the data line voltage from 3.6 V to 3.6 V and 3.6 V ~ 3.5 V, normal should be 4.1 V ~ 4.3 V and 4.3 V ~ 4.2 V, considering the presence of the phenomenon of sound, and sound circuit problems can also affect the data, so check the audio circuits in the first place. Audio waveform measurement have been input IC2101, but no output, audio crystals of oscillation circuit. m4jservice manual download site
 m4jservice manual download site
 m4jservice manual download site
Replace the crystals X2130 troubleshooting. m4jservice manual download site
 m4jservice manual download site
Because of the data bus control circuit, the audio circuit, such as problems may cause other fault phenomena, so when maintenance should be paid attention to.m4jservice manual download site