Power On Troubleshooting - LG U970 Service Manual

4. TROUBLE SHOOTING

4.9 Power ON Troubleshooting

Power On sequence of U970/KU970 is :
PWR key press(Key PCB) → PM_ON_SW_N go to low(VA800),PM6650(U400) KPDPWR_N pin(24)
→ PM6650 Power Up → VREG_MSMC_1.2V(C430), VREG_MSME_1.8V(C431),
VREG_MSMP_2.7V(C420), VREG_MSMA_2.6V(C419), VREG_TCXO_2.85V(C412) power up and
system reset assert to MSM → Phone booting and PS_HOLD(D400) assert to PMIC
VREG_MSMC_1.2V,VREG_MSMP_2.7V,
VREG_MSME_1.8V, VREG_TCXO_2.85V,
Start
Battery voltage. higher
than 3.28V?
YES
VA800 high to low
when key press?
YES
VREG_MSMA_2.6V power up?
YES
Is clock ok?
R406 : 19.2M
X400 : 32.768Khz
YES
Change the Main board
NO
Change or charging the
Battery
NO
Check the Key Dome
NO
Change the Main board
NO
Check the TXCO
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