Huawei YU220, Service Manual

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YU220 service manualV1.0
2013-10-18
Huawei secrets, no dispersion without permission

circuit schematics analysis
：
Part of receiver circuit as show in picture, MIC audio input signal is
differential signal, then the baseband chip MIC input channels, VMICBIAS0
work for the MIC bias voltage.

failure analysis processes
：
Fault：Call opposite cannot listen to voice；
Overhaul flow：check MIC weld whether is OK, can change MIC test; put
through telephone, measure mainboard MIC circuit magnetic bead capacitance
weld whether is completed；
MICBIAS0 whether have2.0v bias; check MIC circuit whether have
tainted stickers, stickers wrong question; additional
welding baseband
chip U301;