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820-00165 no power (U7600 liquid)

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Alex97Lewis

Member
So today I was working on a board which was apparently "sometimes not turning on", had it for a week and was always powering on fine, without inspecting it - I was going to send it back to the customer tomorrow but spotted it wouldn't turn on.

Long story short after inspecting the board, found liquid damage across the U7600 area, three resistors were completely burnt through and believe U7600 was damaged, so replaced it all and still won't power and only pulls around 0.1A.

Don't have many readings at the moment because I'm not with the board now but will do tomorrow morning. I checked PPBUS_G3H and had noticed it was on 1.9V. Injected volts and spotted Q7630 was blown (not surprised) as well as a cap above it so took them off and PPBUS now has ~8V. When I replaced Q7630 the board still wouldn't power up but had 1V coming out of the inductor after Q7630. I sprayed some isopropyl alcohol over the area to see for any shorts and after a minute or so saw a pop come from Q7630 itself. It had blown.

I'm not sure what could be causing this as I've replaced all of U7600 area, and Q7630 keeps blowing.

Really need help with this as its a very stressful board to work on. I understand it would be difficult for anyone to help because of the lack of readings, but if anyone can point me in a direction for what readings are needed, I'll get those as soon as I can!

Thank you
 
2informaticos

2informaticos

Administrator
Staff member
When injected voltage into PPBUS_G3H, with shorted Q7630, you've also injected into PCH.
You should read more threads on the forum, before doing this; PCH may be dead now.

Bad R/C7630, R7631, or their traces, could be the reason why Q7630 gets burnt now.
 
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Alex97Lewis

Member
I will have a look at those you have named shortly as I'm about to have a look at this board again now.

Should I assume that this board is now as good as dead? I do remember that the CPU area was getting fairly warm even with ppbus being on 1.9V, guessing that's because of the Q7630 short.

When I injected volts into ppbus, I did that after replacing both U7600 and its resistors, as well as replacing Q7630 with a known working one so I'm guessing something else might have caused Q7630 to pop
 
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Alex97Lewis

Member
I replaced C7630 and good news! It powers up so PCH isn't dead thankfully.

Bad news is it seems to only like booting up when I spray isopropyl alcohol on top of the U7600. So will be investigating that further.
When there is no alcohol over that area, the board pulls 0.05A, and L7630 only has 0.2V, then with alcohol over U7600 its a full 1V.

Not sure if you may know the possible cause and if readings are required I'll be able to get those now. Sorry for the lack of readings - Never really attempted in-depth board repairs like this, only a case of if I see liquid, replace those parts and not bother with readings (now I'll start keeping a Datasheet of all diode, resistance and volt readings for parts)
 
2informaticos

2informaticos

Administrator
Staff member
Resolder U7600 and be sure to have good traces around.
I suspect some resistor loses correct value.
Change all resistors/capacitors directly, if you have a scrap board available.
 
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Alex97Lewis

Member
In process of that now, will post an update with how this goes, spotted some resistors/capacitors slightly misaligned so will work on this area.
I think it's more likely the U7600 not fully flush with the board, hate working on chips that have thermal pads because I can never seem to use a rework station to get the chip flat on the board as the thermal pad tends to build up with a lot of solder and cause a big bubble of solder. Practice makes perfect I guess.

Thanks for your help so far and will update once this area has been worked on - So glad the PCH isn't dead though
 
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Alex97Lewis

Member
I've noticed that PP1V05_S0 has a resistance of 70Ohms, and on a known working board I have 500Ohm - Assuming something has blown or PCH is in fact damaged in some way? It seems to power up fine but haven't tested with a screen and SSD yet.

I might look at replacing U7600 with another one as I've noticed some damage on the top side of this chip so maybe that's the issue with it not powering on without spraying alcohol over it. All caps and resistors around that area have been reworked and are fully seated.

In diode mode I get 67 with red probe on ground and on a known working board I get 160. These measurements are being taken from C7601
 
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