LG F1200 Service Manual page 75

4. TROUBLE SHOOTING
(1) Checking LDO Circuit
Checking Points
U104
Pin 6 : RF_EN
Pin 1 : RF2.85V
LDO Circuit Diagram
RF2.85V
MIC5255-2.85BM5 U104
5 1
OUT IN
2
GND
4 3
BYP EN
C133 C132
1u 0.01u
Pin1 : 2.85V OK?
LDO Circuit is OK.
Go to the next stage
VBAT
C131 C130
2.2u 1000p
Checking Flow
Pin6
High?
No
Yes
Replace U104
Waveform
RF_EN
RF_EN
- 74 -
Redownload
No
phone S/W
Yes