820-00840 dead, no liquid

[aplas]

Hello,

820-00840 not turning on, no liquid damage, no history (customer told it's dead after sleep mode).

Board without battery, unplugged all connectors takes from charger:
20.33V
0.052A

Power rails:
PPBUS_G3H - 13.7V
PPDCIN_G3H - 20.35V
PP5V_S5 - 0V
PP3V3_G3H - 3.426V
PP3V3_S5 - 0V
PP1V8_S3 - 0V

no short on these rails
no heat through thermal camera

what should I check next?

thanks in advance, your help is appreciated.

 

[2informaticos]

Do you get 3V3_S5/SUS?

 

[aplas]

do you get 3v3_s5/sus?

pp3v3_sus - 0.00v
pp3v3_s5 - 0.00v

 

[2informaticos]

Do NOT quote an entire post, visible few centimeters above.
Maintain forum aesthetic, please.

Post BUF_SMC_RESET_L and SMC_PM_G2_EN levels.

 

[aplas]

Buf_smc_reset_l - 3.424v
smc_pm_g2_en - 3.420v

 

[2informaticos]

Post U7890 voltages.

 

[aplas]

U7890:

1 ssd_pwr_req - 0,33v
2 pmic_en_p3v3s5 - 0,09v
4 pm_en_pvxs5 - 0,00v
6 pp3v3_g3h - 3,42v

 

[2informaticos]

You have a problem on PMIC (U7800) area.
It receives SMC_PM_G2_EN, but doesn't send out enable for 3V3_S5.
Check PPBUS_PMIC, PP3V3_LDO3V, PMIC_SHUTDOWN_L.

 

[aplas]

I've found PPBUS_PMIC 0,01V, R7835 high resistance and C7844, C7843 shorted to ground. Replaced all three components and the system started!

2informaticos Many thanks for your help and patience! You've made a great job!

 

[2informaticos]

I bet was only ONE cap shorted.
For the future, remove one by one and check each time if short has gone...