820-01949 no power

[Kyle93]

this arrived with liquid damage in the u3100 area. Before working on the board it has 20v with low amp draw but did not power on. Replaced resistors and u3100 since liquid was under u3100. Stuck at 5v now with amp meter cycling every few seconds on this port. Using a known good CD3217. All traces and resistors in area look good. LDO voltages are good.

What should be checked next?

 

[2informaticos]

Usually, input voltage cycles when the board tries to start.
Check diode mode to ground on all big coils.
Also check if starts in SMC bypass mode.

 

[Kyle93]

L8100 is only 0.002

 

[Kyle93]

does not start in SMC bypass

 

[2informaticos]

Looks to have short to ground there.
I don't have comparison board, but I don't see a good reason for such low value.

 

[Kyle93]

Replaced Q8100 with no change. Injected 1v before but nothing got warm

On a known good board the value is 0.008

 

[Kyle93]

What should be checked next? Shouldn't the issue with meter cycling on the one port be addressed first?

 

[2informaticos]

Only one port stuck on 5V?
What happens on other port?

 

[Kyle93]

All ports are stuck at 5v. U3100 port has meter cycling turns on and off every few seconds even with a known good CD3217

 

[2informaticos]

The problem may be on the other ports.
U3100 port may cycle because the board tries to start there.
But strange, if you had 20V before touching the board.

The heat might affected something on the board, or moved components.

 

[Kyle93]

Can you advise on what to check or try next?

Have a good board besides this one and all components are present. The only diode measurement that is off is PP3V3_G3H_RTC good board is around .350 but only 0.085 on this board but cannot be a short since 3.3V is still present

 

[2informaticos]

No short, but is very low value.
This may point to bad chip, or filter cap.
The problem is there are many chips and caps connected...

 

[Kyle93]

When injecting 3v nothing got warm. Can this low value be the issue even though 3.3v is present?

What should be removed first?

 

[2informaticos]

Lower value than normal, but too high for voltage injection method.
In this case, should start with the chips which generate voltage for the areas affected by liquid.
Is more or less question of luck...