820-00840 A1708 PP3V3_G3H pulled down

[jadao]

Liquid damage on this one, I found it difficult and time consuming.

1) It had a full short on C6990 PPVIN_G3H_P3V3G3H, replaced the cap and short gone.

2)Next, it had PP3V3_G3H low voltage around 2.2V. Diode mode was showing 0.340 very similar to other working boards however resistance to ground was reading 1.9KOhm.
This was pointing to a 2kohms resistance with other end shorted to ground, indeed I found R5381-pin2 SMBUS_SMC_5_G3H_SCL full shorted to ground. Turned out to be D6950 shorting the signal.

3)SMBUS_SMC_5_G3H_SCL was still reading a low short this time 0.041 in diode mode, additionnaly PP5V_LDO5V was shorted to ground, this time it turned out to be U7800 PMIC witch I replaced.

Now on PP3V3_G3H I have normal readings compare to other boards 0.340 in diode mode and 21kOhm to ground
PP5V_LDO5V is also 0,425 diode mode

My issue: I still have 2.29V on PP3V3_G3H.
If I remove R6999 I can see U6990 outputing 3.4V If I put back R6999 it is pulled down to 2,29V. R6999 measures fine 0 ohm.
If I inject 3,4V on system side I have 14mA draw exactly same with working board.

Can I assume U6990 and U7000 are ok since I get 3,4V on PP3V3_G3H when R6999 is removed? Or I am wrong as I perhaps get 3,4V only because there is no load?

PM_EN_P3V3_G3H is 4,8V and ppbus_g3h is 30mV with no short at all.

I am out of idea and thats why I am here!
Thanks

 

[2informaticos]

U7000 needs to talk with SMC, in order to generate PPBUS_G3H.
0.340 in diode mode at 3V3_G3H looks good, but you should check reverse way measurment too.

"SMBUS_SMC_5_G3H_SCL was still reading a low short this time 0.041"
Was this problem solved?
Must get very similar readings on both SCL/SDA lines.

 

[jadao]

Reverse diode mode reading on 3V3_G3H is normal 1.240 and comparable with other working boards.

Yes diode mode 0.041 on SMBUS_SMC_5_G3H_SCL was solved it was D6950 shorting partially to ground.

I decided to inject 5V on U6990 Vin and enable. It produced 3,4V when 5V was applied after D6905, I mean pin 3 of D6905.
It produced 2.2V when 5V was applied before D6905 (D6905-Pin2).

At that point I knew something was wrong upstream from D6905-Pin2.
I found out odd diode mode reading on D6905.

Black probe on pin3 Red proble on pin 1: Diode mode reading 0.201 ok
Black probe on pin3 Red proble on pin 2: Diode mode reading 0.569 -> should be 0,201 compared to other boards

Reverse diode mesurement was ok.
Replaced D6905 and got stable 3.4V on PP3V3_G3H and nice 13,5V on PPBUS_G3H. didn't know this would affect ppbus_g3H at that point!

After that: I had to replace TPS51980 because it simply never produced 5V_LDO...

Now board fully boots, I have to solve battery detected but not charging...

This is a very nice nightmare practice board with almost 6 different faults completely unrelated on each other...