820-00840 not turning on

[Kyle93]

Arrived not powering on with liquid damage. Before replacing components it was drawing 20V. After replacing U8210 and U650 it somehow went down to 5V.

PP3V42 is present at 3.42V What can cause it to go from 20V to 5V?? What should be checked next?

 

[2informaticos]

Probably corrosion under some BGA chips; could be CD3215, or ISL9239.
Post PPBUS_G3H, voltage and diode mode.
Do you get BUF_SMC_RESET_L?

"U650"
???

 

[Kyle93]

PPBUS_G3H 0.030v

BUF_SMC_RESET_L 3.4v

Typo, it was U7650

 

[Kyle93]

PPBUS_G3H diode 0.385

 

[2informaticos]

Where else did you note liquid on the board?
Try to reflow USB-C input area.
You may need to reball CD3215 chips.

 

[Kyle93]

only areas were U7650 and CD3215 area along with audio section. CD3215s were reflowed

 

[2informaticos]

Looks like CD3215 area reacted to the heat when you've changed the chips.
Try reballing both of them.

 

[Kyle93]

Replaced CD3215 that had liquid spill and its now solved.

 

[Kyle93]

not solved. After ultrasonic board only drawing 20v at 0.01a

noticed small bridge on Q7860. Fixed bridge powered again then smoked in area. Replaced Q7860 and booted successfully once. Now stuck at 0.01a again and PPBUS_G3H is shorted 0.001 diode mode.

Any way to find short without injecting voltage?

 

[2informaticos]

Bad news .

"Q7860"
Do you mean Q7680?
I cannot find any Q7860 in schematic...

Check ohm mode at PPBUS_G3H and all big coils, especially CPU ones.
Any has the same value as PPBUS_G3H?
Don't forget L7690, as you had problem there.
Be sure R7684/85/86 and C7689 are good, as traces too.

 

[Kyle93]

yes, I meant Q7680

PPBUS_G3H ohm value the same as all the big coils around 1.2

Replaced R7686 and C7689 but still no change. The R7684 and R7685 measured normal

 

[Kyle93]

L7690 is good as well

 

[Kyle93]

Bad Q7680 caused PPBUS_G3H short. Replaced and PPBUS_G3H back to 13V but board only drawing 0.04 and 0.05 amps.

What to check next?

 

[2informaticos]

Overvoltage on L7690 could be letal damage.
Check basic signals for power on sequence.
Do you get 3V3_S5/SUS?

 

[Kyle93]

PP3V3_S5 0V

PP3V3_SUS does not appear on board view

 

[Kyle93]

PP3V3_S5 is shorted. Should voltage be injected to find short?

 

[2informaticos]

Which is the exact ohm value to ground?
First remove U7650 and Q7660, one by one; and check value each time.
If still low value, then you can inject, if is the case.

 

[Kyle93]

1.6 without Q7660 and or Q7660 removed

 

[2informaticos]

1.6 ohm is really problem now.
You can start injecting with 2V, no more than 4V in any case.