820-3536-a wont turn on

[Gannons3]

I have an 820-3536-a macbook pro retina, I get an amber light on the charger, but the computer wont turn on, I am missing pp5v_s4, pp5v_s5 is presant. board was water damaged, thanks for any help

 

[aprendiz]

Check if pp5v_s4 is pulsing, you may need an oscilloscope, pulses are pretty fast and DMM may not catch it....

Also check for water damage around U6100 and U1900...

 

[Gannons3]

as far as i can tell pp5v_s4 isnt pulsing, but i dont have an oscilloscope. there was some blue along the 1-4 pin side of U1900 and the ground pin of U6100 had some aswell

 

[larossmann]

check the traces between the resistors around U6100 and the CPU

 

[Gannons3]

The only area that seems to have bad traces are the probe points on the pins 1-4 side of u8330

 

[dukefawks]

Look up all the termination resistors in the data lines of U6100 and check them all. Also check continuity between them all. I think there are 16 of them.

 

[Gannons3]

the only resistor that i found that was not what the schematic said was r6131, resistance was 77k ohms but theres no resistor on the board there; and its also not labled "no stuff"

 

[dukefawks]

Voltage on PPVRTC?

 

[Gannons3]

I am getting 274 mv on ppvrtc_g3h

 

[dukefawks]

Yeah, there is your problem. Check around U1900, usually corroded pins or dead. Also check resistance to GND on PPVRTC rail.

 

[Gannons3]

U1900 had pins 1-4 pretty corroded, pin 1 definiately the worst of them, getting anywhere from 3-8 ohms resistance to ground on ppvrtc

 

[dukefawks]

3-8 Ohms with U1900 removed? Is way too low of course, should be in the Ks.

 

[Gannons3]

I took u1900 off the board and got 2 ohms resistance to ground :/

 

[larossmann]

Most likely bad CPU and this is junk.

Sometimes it is a short that can be worked around, such as in this case: fast forward to 1:30:00 to see me fix a case of 0 ohms to ground on a board with shorted PPVRTC_G3H that is very similar to yours.

https://youtu.be/RtHRwZxvjME?t=5434

 

[dukefawks]

There is a few caps on the PPVRTC line to GND. Take them all off, if there still is a short the CPU is dead.

 

[Gannons3]

took off c1910 resistance to ground is now around 30m ohms

 

[Gannons3]

okay i replaced c1910 and u1900 i now get 3.35 volts on ppvrtc_g3h board still doesnt power on; also still missing s4 power rails

 

[dukefawks]

Check carefully for power cycling on the 5V bus L7520. PPBUS present at 12.6V? 3V at L7560?

 

[Gannons3]

ppbus is at 12.6v theres 3.34v at l7560 if theres 5v cycling at l7520 my meter just reads a steady 0

 

[dukefawks]

Check if U1900 is putting out 32kHz RTC signal.