820-00840-A not starting

Fanfwe

Member
Hi, I have this 820-00840-A board with liquid damage around U7650 and the backlight stuff also.
I've narrowed it down to U7650 not creating PP5V_S5 and that's due to PMIC_EN_P3V3S5 missing.

So, checking around PMIC, I could see that PP3V1_RTC is good, PP3V3_LDO3V is good, PP1V25_VREF is good.
PMIC_SHUTDOWN_L is high.
On this board, R7828 is the one present.

What should I check next ?
 

Fanfwe

Member
PPBUS is 13.02V
And yeah I should maybe have started there, but no issue with the CD3215 stuff, of course. 20V from charger, which also implies 3v3_g3h is indeed present.
 

Fanfwe

Member
Diode mode and resistance to ground:
L7670: 0.407V 900Ohms
L7690: 0.353V 780Ohms

PPVCCGT: 0.0023V 4.6Ohms
PPVCCCPU: 0.0043V 9Ohms
PPVCCSA: 0.0066V 13.37Ohms
PPVCCPCH: 0.0652V 130Ohms
PPVCCIO: 0.0531V 106Ohms
 

2informaticos

Administrator
Staff member
Check solders, traces and all the components around U7650.
Change the chip, just in case.
Check diode mode at 5V_S5.
 

Fanfwe

Member
Diode mode at 5V_S5 is 0.410V, so there's no short.
Traces, solders and probe points look okay, and I have tested continuity for the few ones I had a small doubt, they are all good.
I guess I'll try to replace the chip, just in case as you said, but I can't see how it can be the issue when the enable signal is low (and not shorted to ground)
 

Fanfwe

Member
Yeah that's what I thought too. I don't have any right now. I'll put this aside for now and report back later once I get some and replaced it.
Thanks
 

Fanfwe

Member
No, no pulse. It goes from floating state to 0V when I connect charger and that's it. And I do get the LDOs (PP3V1_RTC, PP3V3_LDO3V, PP1V25_VREF) with the new chip too.
So, you suggest that I try again with another U7800 ?
 

Fanfwe

Member
Do you know what's required as input on U7800 for it to make PMIC_EN_P3V3S5 high ?
PMIC_EN_P3V3S5 is PGD, so does that mean that it needs VSD to be good ? Or VSA, VSB, VSC, VSD all need to be good ?
I assume VSx stands for Voltage Sense, and PGx stands for Power Good, so I'd expect PGD to turn on if VSD is good, but maybe there's additional logic that requires other voltage sense to also be good so that power rails turn on in sequence ?

What about the STANDBY# pin of U7800 ? Can it have an effect on PMIC_EN_P3V3S5 ?
 
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