Power On Trouble - LG U300 Service Manual

4. BB Trouble Shooting

4.8 Power ON Trouble

Power On sequence of U300 is :
PWR(END) key press → PM_ON_SW_N go to low(D601),PM6650-2 KPDPWR_N pin(24) →
PM6650-2 Power Up → VREG_MSMC_1.250V(C436), VREG_MSME_1.8V(C437),
VREG_MSMP_2.7V(C428)
VREG_MSMA_2.6V(C424), VREG_TCXO_2.85V(C418) power up and system reset assert to MSM →
Phone booting and PS_HOLD(D400) assert High to PMIC(PM6650-2).
Start
Battery voltg. higher
than 3.28V?
YES
Press PWR key
Keypad LED on?
YES
D601 high to low
when key press?
YES
YES
Is clock ok?
R411,C438 : 19.2M
X400 : 32.768Khz
YES
Change the Main board
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4. TROUBLE SHOOTING
NO
Change or charging the
Battery
NO
Follow the LED trouble
shoot
NO
Check the Diode
NO
Change the Main board
NO
Check the TXCO