820-2879 no power

[peterfixit]

I have an 2879 with no power
initially came in a month ago for no green light no fan spin, fixed no green light by replacing R6905
was checking rails found 3.3v s3 missing, traced back to R7812, missing PM_SLP_S4_L
rabbit hole or not?

 

[dukefawks]

These do not auto power on, short power pads. Also what is resistance to GND on 3V42 rail?

 

[peterfixit]

0.273@c6999, partial short?
shorted smc_onoff_L to ground and nothing

 

[aprendiz]

RESISTANCE to GND on 3V42 rail, not diode mode...

 

[peterfixit]

36k at c6999

 

[dukefawks]

That could be ok. 3V3_S5 present?

 

[peterfixit]

3.3V dead on pin 1 R1987

 

[dukefawks]

PPBUS even present? TPS51125 area?

 

[peterfixit]

ppbus 12.61@C7331 , U7200 area was replaced, if i remember correctly the whole place looked messed up

 

[dukefawks]

There is your issue. U7200 makes 3v3_s5. G2_EN present?

 

[peterfixit]

SMC_PM_G2_EN R7273 pin1 3.406v, pin 2 0v, after replacing i get both sides 1.4 Vto 4V, could u7840 be bad? pin 4 u7840 is 0.398volts

 

[larossmann]

R7273 is for PP5V_S5, not PP3V3_S5. What do you get for P3V3S5_EN_L?

 

[peterfixit]

0.365V at pin 5 Q7221 2.990V at pin 2 Q7221

 

[dukefawks]

"after replacing i get both sides 1.4 Vto 4V"

Well that is messed up. This means G2_EN is now pulsing? Pretty sure something around U7200 or U7200 is messed up.

 

[peterfixit]

replaced u7200 no change, 1.6v on charger output, no shorts on pp3v3_s5
p5vs3_EN_L is 3.3V
p3v3s5_EN_L is 0.3v
smc_pm_g2_en 0.185v
removed u7840 and got 3.4v on pin 1, 1.28V on pin 2, 0.21V on pin 3, 3.3v on pin 6, 0.8v on pin 7, 0v on pin 8

 

[dukefawks]

G2_EN is the problem. If it is not pulsing I suspect SMC problem.

 

[peterfixit]

ok ive tested and, R7273 i get 0V, at pin2 u7840 i get 0V
so smc replacement? from what ive heard I have to pull another smc off the exact same model, is that right?

 

[nate8organic]

that is right about the smc, needs to be the exact same model. first try to reflow the smc just in case a ball is corroded or not connected sometimes this works and saves time and a smc. if that does not work remove the replacement and old smc very well so that you can just seat the replacement without reballing it.

 

[peterfixit]

ok reflow and no change, I dont have the exact board to replace it with so this will have to go on hold unless there are any other ideas

 

[peterfixit]

please mark this as closed as the owner has cancelled the job, thanks for the assistance