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Power On problem 820-2879

bighead

bighead

New member
Hi guys,

I've a 820-2879 here with a power problem.
This one is not liquid damaged. Lot of dust in the computer, but no liquid damage.
The problem is that it turns on sometimes and it works ok, but lot of times it won't turn on.

Some measurements:

When it's not turning on:

PPBUS_G3H - 12.55V but goes down and up.
PP3V3_S5 - jumping between 3.3V - 1V

Sometimes everything goes down to 0V and stays there until I disconnect and reconnect the charger.

SMC crystal is oscillating.

I changed U7200 I thought I've a problem with the PP3V3_S5 line.

There is no short on PP3V3_S5 nor on PP5V_S3

Any idea?

Thank you!
 
bighead

bighead

New member
Yes, looks like those are stable even when it's not turning on.

PP3V42_G3H - 3.4V
SMC_RESET_L 3.2V
SMC_PM_G2_EN 3.3V

I also have the 3.3V(P5V3V3_REG_EN) on U7200 all the time.
 
bighead

bighead

New member
When it's fluctuating its between 12.55V - 12V on the scope. The thing is that it's not always fluctuating. Sometimes it just goes down to 0V.
 
bighead

bighead

New member
Back to this board. Yes, sense resistors and traces are all ok.

So just to make it clear. PPBUS_G3H goes up to 12.56 it's there for 2 sec and collapse.
I believe the problem is that the PP3V3_S5 rail is all over the place. There is no short on the 3.3V rail.
However if I heat the board just a little bit everything is fine, but when it cools off the problem comes back.

I checked the traces to q7220 all seems ok.
 
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