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820-01958 liquid damage

B

Blackmambo90

Member
Hi all,

Have this board in with "no backlight" issue
After inspecting i saw that it is a water damage and that most of the damage is around backlight circuit.

Replaced affected components, repaired traces, try to power on - all work

Power off the unit and went to tea break..

After coming back i saw that the unit is off but the cpu is warm... start to inspect and saw that it does not power on anymore..

Now it act this way:
Battery connected take 20v 0amp
Battery disconected take 5v and 0.06amp

The power light on the board pulse

What i noticed is that when i was cleaning/fixing water damage is that there was a strange behavior around damaged caps:

On doner board on one side it was ground and on the other it is 1mohm however on this board it was 20ohm... and now at this exact spot it is shorted to ground..

Unfirtunatly dont have the right board view for that board so dont even know where that goes but at one point during my cleanup/repair i took measurements and it vas 3.something volts at those pads...
Attached images is the caps i am talking about on the donor board..

Any idea what to look for now?
Many thanks
 

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B

Blackmambo90

Member
Ps. Last time i was searching i was not able to find the board view... did a quick search now and found it 👏
Didnt had time to look at it yet, but here it is in case it might be useful:
 

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2informaticos

2informaticos

Administrator
Staff member
It comes from 3V3_G3H, through R5520.
So the short can be in any point of 3V3_G3H power rail.

Use voltage injection method.
Start with 1V, no more than 4V (if needed).
Set PSU to max amp first.
Use high amp rated wires; need to heat the board, not the power cables.
 
B

Blackmambo90

Member
Hi @2informaticos,

Yes, just took a look at it and also removed r5520 -> still short.. went ahead and removed c8150, c8164, c8161 and u8150... still short... so i presume somewhere in layers the issue is....

Should i inject the voltage?
 
2informaticos

2informaticos

Administrator
Staff member
So, after removed R5220, the short remains on its pin 1?
Then inject voltage on this point; as above described.
 
B

Blackmambo90

Member
But there was the issue with pads off the caps from the first photo. They vas rusted/melted and i had to cut them and apply green mask
Maybe i didnt clean well and there is coal left... will try to remove mask and clean it more...

Any other ways to find the short between layers? I read that if you apply voltage to between layers short, it will make more coal and more damage... is that true?
 
B

Blackmambo90

Member
Ok after another cleaning it look good, no more short.. however it still have the same behavior of not powering on, stays at 5v with out battery and the light on the board is flashing... no PP3v3_G3H is at 0 volts...
 
B

Blackmambo90

Member
Ok, the flashing light is due to PP3V3_G3H_RTC that cicle around.. so no 3v3 on it... but it come and goes.. no short
Mesured at R6979
 
B

Blackmambo90

Member
Yes, ppbus_g3h fluctuate as well between 5and 12v
And no the board does not turn on with battery and charger, how ever it goes to 20v on usb c and U7800 get very hot...
 
B

Blackmambo90

Member
Ok, no short on them... how ever on L7816/17 donor board show 80ohm and this one 55ohm
L7806/7/8/9 shows 12ohm and 19ohm on donor board... dont think its critical...
 
B

Blackmambo90

Member
Ok found the short:
All small caps around U7800
C78B0/1/2/3/4/5/6/7/8/9
On the PP3v3_G3h_pmu_vvdmain

Edit: ok the pp3v3_g3h is shorted now... strange...
 
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