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820-2850-A Liquid Damaged With Some Heating and Low Resistance to Ground

rany

rany

New member
I fixed WD 820-2850 by jumping wires to replace corroded vias/traces from R7052 to R7050, and replaced R7052.
U7971 was nicked and J5815 was destroyed with its traces from prior pry damage. Replaced them both. Near them were some corroded components that I replaced.
Q7055 was corrosion underneath it, removed it and cleaned everything. Not sure if I replaced it, forgot to take note and the laptop sat for some time waiting for a new battery.
Now the laptop runs almost normally except that it charges extremely slow and discharges quickly, and I felt some heat coming from Q7635, L630.
Tested the line between them and I got 13 OHM resistance to ground. I narrowed this low resistance to PP1V05_S0. Is this normal in any way? Never worked on this line before and have no idea!
Note: U7971 which I had replaced has nothing to do with it. Removing it doesn't change resistance to ground of PP1V05_S0.
 
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rany

rany

New member
I will, but even with Q7055 removed, I have that same low resistance between PP1V05_S0 and ground = 13OHM. Is it normal?
 
rany

rany

New member
aprendiz said:
Absolutelly normal..... ohm´s law, low voltage/high current = low resistance
Click to expand...

I have to close shop. Will test tomorrow the charging and see if it changed after replacing Q7055.
And so the lesson is I don't have to hunt for a short to ground on PP1V05_S0 because it will normally have low resistance?
If yes, reminds me of the first time I thought I found shorted caps on the line going under the iPhone CPU.
 
rany

rany

New member
OK this is becoming interesting.
Before I replaced Q7055, it was charging very slowly.
I replaced Q7055 and got "battery not charging" and no orange light, only green. 3V42 is present.
As I said before, I noticed heat next to U9600, and I noticed that if I tap U9600, fans stop from spinning (still with green light on charger), then they start again.
Should I reball or reflow? I am afraid some silicone/glue crap will go underneath it.
And should this resolve my issue of no charging?
 
larossmann

larossmann

Administrator
Staff member
U9600 has nothing to do with anything other than screen flicker/distortion. Are you sure we're looking at U9600 here?
 
rany

rany

New member
Yes I am sure it is U9600. By the time you replied I had reballed it.
I can confirm also that it was not causing the interruptions because it is still doing it, though less. Heating may have reflowed something although I can't see what?!
LD was around U9600 and I found what seem to be oxidized pads on the chip, and the image did flicker sometimes so I hope I did not do useless work.
Before replacing Q7055 as suggested by apprentiz, I had slow charging and orange light. After replacing "no charging" and only green light.
First time I worked on it, via from R7052 to R7050 was corroded and I had to jump. So I poked around and found missing line between Pin 4 of Q7055 and Pin 16 of ISL. Must have failed during last rework. After jumping CHGR_BGATE the laptop is back to charging and orange light, BUT still restarts if I poke next to U9600. Not sure if this is something I need to address?
I am going to test speed of charging now.
 
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rany

rany

New member
- Charging normally, this is solved.
- Wasted time on U9600 but I'd like to think I may have saved it from near future failure since the pads were oxidized.
- Still some heat near U9600 and poking there still restarts laptop! Otherwise working normally.
I'm handing it back to client having solved what he brought it for: started with LD leading to no charge then no boot when lines got corroded.. That's solved.
 
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rany

rany

New member
larossmann tried to upload picture of U9600 with oxidized pads. Got => Error while saving content: SyntaxError: JSON Parse error: Unexpected identifier "Forbidden"
 
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