Power On Trouble - LG U990 Service Manual

4. TROUBLE SHOOTING

4.7 Power on trouble

Power on sequence of KU990 is :
PWR key press → PM_ON_SW_N go to low (VA700, PM6650-2M KPDPWR_N pin#24) → PM6650-
2M Power Up → VREG_MSMC_1.2V(C560), VREG_MSME_1.8V(R520), VREG_MSMP_2.7V(R513),
VREG_MSMA_2.6V(R508), VREG_TCXO_2.85V(C510) power up → PON_RESET_N assert to MSM
→ Phone booting & PS_HOLD(D500) assert High to PMIC(PM6650-2M)
Battery voltg. higher
than 3.2V?
Press PWR key
Keypad LED on?
VA700 high to low
when key press?
VREG_MSMC_1.2V,
VREG_MSMP_2.7V, VREG_MSME_1.8V
VREG_TCXO_2.85V,
VREG_MSMA_2.6V power up?
Is clock ok?
X100 : 19.2M
X500 : 32.768Khz
Change the Main board
LGE Internal Use Only
Start
NO
YES
NO
YES
NO
YES
NO
YES
NO
YES
Change or charging the
Battery
Follow the LED trouble
shoot
Check open Pattern
of power button
Check Dome Sheet
Change the Main board
Check the TXCO and SLEEP CRYSTAL
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