LG C3400 Service Manual page 65

4. Troubleshooting
Checking Flow
START
Check Battery Voltage
> 3.35V ?
YES
Push power-on key
And check the level change
of PWRKEY
YES
Check the voltage of
The LDO outputs at U102
YES
Logic level at KEYON of U102
= HIGH
YES
Does it work properly?
YES
THE PHONE WILL
POWER ON.
NO
Charge or Change Battery
NO
Check the contact of power key
NO
VCORE=1.8V
VMEM=2.8V
VRTC=1.8V
VSIM=1.8V or 2.85V
VAPP=3.0V
VVBACK=1.8V or 2.8V
NO
NO
The power-on procedure is
Completed. The problem may
be elsewhere.
- 64 -
Or dome-switch
Replace U102
VVCXO=2.75V
VUSB=3.3V
VEXT=2.8V
VABB=2.75V
VMIC=2.5V
Re-download software
Does it work properly?
NO
Replace the main board