A1708 820-0840-A no power

[hgoncalves]

Hi,

I have an A1708 820-0840-A that hat a very small liquid contact, and has no power. Ampmeter stays black, and i get no voltage on F3000.
C8167 was oxidated and i removed (looks that was the only point with liquid contact).

After removing C8167, i notice that PP3V3_S4, on diode mode, and ohm reading oscilates a lot (diode readings oscilates bettwen 0.485 and 0.086. ohm reading oscilates bettwen 45k ohm and 5k ohm).

Can you help?

 

[Vogelek23]

First of all, have you inspected USB-C ports? Are they clean and free from corrosion? If so, what is the resistance to ground on F3000?

 

[hgoncalves]

They look clean and F3000 has 2.5K ohm of resistance to ground

 

[2informaticos]

Check diode mode to ground on the CC1/2 pins of the CD3215 chips.

 

[hgoncalves]

It looks that U3100 is shorted.
Diode readings:
U3100
CC1=0.041
CC2=0.122

U3200:
CC1=0.545
CC2=0.550

 

[2informaticos]

Two bad readings point to bad U3100...

 

[hgoncalves]

Hi,
I've replaced U3100 and now i get 5V on one usb-c port and 5V on F3000.
However, on the other usb-c port i get black ampmeter, and 0V on F3010, but diode readings on CC1/2 of U3200 are the same as U3100 (good)

 

[2informaticos]

Compare diode mode readings between U3100/200 on various points; especially the lines connected to J3300.
Also check U2890 and adjacent components.

 

[hgoncalves]

Hi,
It seams that I have a short in PP3V3_UPC_XB_LDO.
C3208 has 0.0006 in diode reading.

 

[2informaticos]

Very likely bad U3200.
You should remove C3208 and test again.
Be aware, PP3V3_UPC_XB_LDO splits into more rails; look at pages 28 and 69.

 

[hgoncalves]

Hi,
After removing U3200 the PP3V3_UPC_XB_LDO short is gone, but afetr I replaced U3200, now i get 5.15V on both usb-c ports

 

[2informaticos]

Do you get correct LDO rails for CD3215 chips now?
Check in voltage and diode mode.

Any other voltages appear on the logic board?
What happens if you connect known good battery, with some charge?

 

[hgoncalves]

OK,
the first cd3215 (U3100) was bad (don't understant why, because the readings were the same as the U3200). After replacing it, it started to work again.
TKS