External Audio - Nokia 301 Service Manual

RM-839; RM-840; RM-841
System Module
Microphone
The internal microphone is placed on PWB below the keypad, which is a SMD analog microphone.
The microphone circuit is configured in pseudo-differential mode (Wheatstone bridge) for better noise
performance. The affected components in the Wheatstone bridge are: R2825, R2826, R2827, R2828 and
C2837.the bias voltage put into MICP1 from VMIC, the affected components are: R2824 and C2836.
Figure 56 Internal microphone
Figure 57 Internal MIC bias circuit

External audio

External audio is circuit loop mainly related to basic headset which use its own microphone system.
Issue 1 NOKIA INTERNAL USE ONLY Page 6 – 27
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