820-3476 Dead, no 5v power rail

[Imyk]

So I have this water damaged A1502 MBP 13" Retina, it was very light water damage, as no apparent physical signs of corrosion.

PPBUS_3GH is good, all PP3v42 are good.

NO PP5V_S5.

U7501 is receiving 3.3 @ VIN but no voltage at SMC_PM_G2_EN , S5_PWR_EN or P5VS4RS3_EN.

I do get a faint green light on the charger, no fan spin.

However one random time I plugged in the magsafe to test voltage, the charger showed a solid bright green / orange light.
PP5V_S5 was showing 4.1 volts after unplugging and re inserting the magsafe, the charger went back into faint green light, and no power at PP5V_S5

I am no expert when it comes to this stuff, so bear with me in my explanations.

Where should i start checking first? Does SMC_PM_G2_EN need to be present before S5_PWR_EN?.

EDIT: I went through the power rails one more time. I am now getting a short to ground on PPVRTC_G3H and PP3V3_S5, Also it seems as if someone attempted board repair prior to me receiving it, C1910 is gone, looks like it was scratched off when trying to probe.

 

[dukefawks]

First thing is to get a good green light that turns orange after 3 seconds. Is ACOK coming high from ISL6259? SMC_RESET high? Voltage on PPBUS?

 

[Imyk]

Duke,

Voltages are -
SMC_BC_ACOK - 3.3v
SMC_RESET_L - 3.3v
PPBUS_G3H - 12.3v

Adapter_sense is getting 3.4v, does that prove that the sys_onewire is working?

I am getting 16.7v on either side of DC IN fuse (F7005) as well as PPDCIN_G3H

 

[dukefawks]

PPBUS at 12.3V means the SMC is probably not running. Probably crap under the SMC, apply some flux and heat to SMC. Do not fully reflow, just 150-200C heat to clear the crap under it.

 

[Imyk]

Okay I will try that and post my results, would crap under the smc cause all of the shorts I'm having on the 3v3 rail?

 

[Imyk]

Duke,

After semi reflowing the SMC, as suggested, I now get a solid green to orange light.

PPBUS_G3H is now 4.2v
PP3V3_S5 is now 1.2v
PP5V_S5 is now 4.1v

I assume these voltages are still too low for normal operation?

 

[Imyk]

Just another note, when leaving the magsafe plugged in, the CPU area temperature goes from about 86-120+ F.
Is this a case of dead CPU?

 

[dukefawks]

PPBUS is way too low, measure resistance to GND. Check if PPBUS is shorted to CPU Vcore because I think it will be.

 

[Imyk]

Duke,

When checking in Diode / Continuity mode, PPBUS to ground is showing 145 drop, PPVCC is showing 40 drop.

PPBUS is showing 89 Ohm resistance to ground
PPVCC is showing 23.9 Ohm resistance to ground

Resistance to each other is 179 Ohms

 

[Imyk]

Is this indicating a short on PPVCC? I recall in a video from Louis that it isn't a significant enough drop on a major power rail to call it a short.

 

[dukefawks]

PPBUS should be way higher than 89 Ohm. Measure from PPBUS to all the coils to see if there are any FETs shorted on the high side. Anything under 89 Ohm is of course suspect then.
24 Ohm on PPVCC is not a problem

 

[Imyk]

Duke,

Just so I can confirm before posting results, You are requesting the readings between PPBUS and the source side of the FET?

Just not sure what you mean by the "high" side, other than the source side. Or do you want readings at the drain?

 

[dukefawks]

Between PPBUS to any of the coils.