SOLVED: A1707 820-00281 - 20V 0.02A after liquid damage

[it-solve]

Hi Guys, have got this board with mild liquid damage. Multiple corrosion points, mainly around charging ports.

R2890 was fallen off, replaced now
C3501 knocked off, left off as filter cap

Usb charging voltage is up, but I'm missing output from U7000


SMC_RST_L - 3.3V
PP3V3_G3H - 3.3V
HPWR_EN_L - 3.3V
TBA_VDDA - 5V
PPDCIN_G3H - 20V
PPBUS_G3H - 0.3V
PPVBAT_G3H_CHRGR_R - 0.3V
PM_EN_P3V3_G3H - 5V
SMC_BC_ACOK - 3.3V

Seems like its failed U7000, what you guys think? Shall I replace and retest or is there something else to test before it?
No visible shorts or unexpected heat signatures

Thanks

 

[2informaticos]

Did you check diode mode to ground on PPBUS_G3H?
F7000/1 are good?

I didn't see TBA_VDDP voltage.
Be sure all R/C7030/40 and traces are good also.

 

[it-solve]

Sorry, havent posted it as same as VDDA

Traces seems to be alright at TBA_BOOT

TBA_VDDP -5V
TBA_BOOT1_RC - 4.7V
TBA_BOOT2_RC - 4.7V


Fuses are fine, though PPBUS_G3H to ground 0.1VDc or 111Ohm
Inject at PPBUS?

 

[2informaticos]

Two high ohm value for voltage injection.
Did you check reverse reading on diode mode?
Any big coil with the same reading?
If not, remove F7000/1 and see which side remains this value.

 

[it-solve]

Two high ohm value for voltage injection.

What would you say is reasonably lower resistance which can accommodate voltage injection? Under 50 Ohms?

Yes, this is reverse reading in diode mode 0.111Vdc

Other coils with same low readings are:

L7960 - 0.11Vdc
L800 - 0.06Vdc
L7900 - 0.26Vdc

L7410/20 - 0.01Vdc
L7211/21/31 - 0.006Vdc

When Fuses removed 0.05Vdc is on PPBUS_G3H side

 

[2informaticos]

"Yes, this is reverse reading in diode mode 0.111Vdc"
I just asked about second reading, reversing probes...

Now check resistance between PPBUS_G3H and L7960.

 

[it-solve]

Apologies, I thought you meant reverse being black probe to ground.


0.04Vdc - Red on G3H - Black to Ground
0.08 - 0.1Vdc - Black on G3H - Red to Ground

G3H to L7960 short 0.5 Ohm

 

[2informaticos]

Replace U7960 and test again...

 

[it-solve]

Spot on @2informaticos Thank you again