820-3437 water damage around SMC

djdblaster

New member
Board was water damaged. Cleaned with UC. Damaged areas showed in pictures. After cleaning, looks pretty good, including under SMC.

Rails present & stable:
PPBUS
PP3V42
PPVRTC
PP5V_S5
PP3V3_S5

Not present:
PP5V_S4 0V
PP3V3_S4 0.235V
 

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2informaticos

Administrator
Staff member
Did you reball SMC?
Does it start in SMC bypass mode?
Check PM_SLP_SUS_L and 3V3_SUS.
Any pulse (at least) at PM_SLP_S4_L?
 

djdblaster

New member
I haven't done anything to SMC yet.
It doesn't start in SMC bypass mode.
PM_SLP_SUS_L - 3.3V
PP3V3_SUS - 3.3V
PM_SLP_S4_L - 0.02V (no pulse)
DCPS shows 30mA steady draw. It hangs somewhere.
 

JohnB8812

New member
You must flux and heat the board at least before UC....likely crap under the SMC still also could have an issue with TPS51980, clock chip, Q8150, U1950 etc. First, reflow the SMC and see if any change
 

djdblaster

New member
Okay. Before I do that, I went around a bit and found PM_SLP_S4_L having 3.5Ohms. So hopefully not PCH or SMC pulling it down... Should I first try to remove other components on that rails and check?
 

2informaticos

Administrator
Staff member
There are few chips you can remove before; U2030/3510/4810,
Look if R1461 has no corrosion around.
If still low value, put good flux and heat SMC first; next one, PCH.

I stillrecommend to reball SMC.
Don't forget to check if short is gone when SMC is removed.
 

djdblaster

New member
Okay, I lifted mentioned chips (except SMC and PCH, of course) and nothing changed. Then I heated SMC with flux and PM_SLP_S4_L is back to 100kOhms.

I wanted to check for PM_SLP_S4_L value and checked wrong resistor (R1995) instead of R1461. Basically, R1995 shows PP3V3_S0 being 0 Ohms.

Power hasn't been pushed through motherboard. I'd rather like to probe around for shorted things instead of pushing power.

Am I thinking logically here?
 
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2informaticos

Administrator
Staff member
Never power up the board if you detect a short.
In this case is safe to inject voltage on 3V3_S0 line.
Start with 1V, and go high maintaining ampers bellow PSU current limit.
However, stop before reaching 4V...
 

2informaticos

Administrator
Staff member
If you get two (or more) different power rails shorted to ground, and both (all) go to a common chip, guess which is the culprit...
 
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