Power On Troubleshooting - LG CU405 Service Manual

4. TROUBLE SHOOTING
4. BB Trouble Shooting

4.6 Power ON Troubleshooting

Power On sequence of CU405 is :
PWR key press(Key PCB) → KEY_ON_SW_N go to low(D601),PM6650 KPDPWR_N pin(24) →
PM6650 Power Up → VREG_MSMC_1.25V(C434), VREG_MSME_1.8V(C435),
VREG_MSMP_2.6V(C427), VREG_MSMA_2.6V(C425), VREG_TCXO_2.85V(C414) power up
and system reset assert to MSM → Phone booting and PS_HOLD(D400) assert to PMIC
VREG_MSMC_1.25V,VREG_MSMP_2.6V,
VREG_MSME_1.8V, VREG_TCXO_2.85V,
LGE Internal Use Only
Start
Battery voltg. higher
than 3.28V?
YES
D601 high to low
when key press?
YES
VREG_MSMA_2.6V power up?
YES
Is clock ok?
R405 : 19.2M
X400(pin1,4) : 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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