LG KS20 - Speaker Phone Path

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Only for training and service purposes
4. TROUBLE SHOOTING
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4.19 Speaker phone path
MSM7200 LINE_OP,LINE_ON → C402/R403, C401/R402 → Speaker AMP(U401) → 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
Sine wave appears at
C402/R403 and C401/R402?
Change the Main board
NO
nSPEAKER_SHDN(TP400) is
2.6V?
Change the Main board
NO
YES
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
YES
The sine wave appears at
SPK+?
Change the Main board
NO
YES
Check an U100 SMT status
by X-ray
Exchange U100 or
Change the Main board
And Retest