LG KF390 Service Manual page 104

4.12.4 Speaker Path ( MP3 , Speakerphone , Key tone )
Signal Pass : MSM6280 Line_N/P → U401 ( Amplifier ) → FB404 / FB405 → CN403 → Speaker
Start
Remove rear-case and
Connect the speaker
Check Connector Status and speaker wire
Does you see the waveform
at C420 / C419
No
Check Amplifier(U401 ) and
component status
Good
Change the Main board
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Only for training and service purposes
4. TROUBLE SHOOTING
SPK+
Yes
Change the
Speaker
Bad
Replace U401 or
Re-solder
- 105 -
SPK-
C419 C420
22p 22p VA415 VA416
LGE Internal Use Only
CN403
1
2