LG KS20 - Receiver Path

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Only for training and service purposes
4. TROUBLE SHOOTING
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4.17 Receiver Path
MSM7200 EAR1_OP, EAR1_ON → R103, R104 → Analog Switch(U400) → R421, R420 →
CN400 → CN602 → R751, R750 → L703, L702 → CN701 → Speaker
Start
Connect the phone to network
Equipment and setup call
Setup 1KHz tone out
NO
Can you hear the tone?
YES
END
Sine wave appears at
R103, R104?
Change the Main board
NO
The sine wave appears at
Pin 4, 1 CN400?
YES
The sine wave appears at
SPKR_N,SPKR_P SUB PCB
Check SUB PCB.
Check CN602
YES
NO
Change speaker
NO
The sine wave appears at
SPK+?
Change the Main board
NO
YES
YES
Check an U100 SMT status
by X-ray
Exchange U100 or
Change the Main board
And Retest