Huawei YU220 Service Manual page 38

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
tainted stickers, stickers wrong question; additional
chip U301;
2013-10-18
YU220 service manualV1.0
have2.0v bias; check
Huawei secrets, no dispersion without permission
：
：
MIC circuit
welding baseband
whether have