820-00928 20V Not turning on

Client brought in a macbook - 820-00928 that wasn't turning on.

It takes in 20V .1A- .8A fluctuating on all 4 ports
Liquid damage on U3906 area
No Voltage on Big coils

Cleaned up corrosion
Lifted U3906 removed corrosion.
With a new known good battery it takes 2-3A - cpu doesnt get hot

PPBUS_G3H is present
PP3v3_SUS is present
CPU Lines not present / 2OHMS to ground
SMC Reset/Bypass made both fans spin at max w/ new battery but no display

Seems like its trying to turn on but cant complete the sequence
 

2informaticos

Administrator
Staff member
Do you get CPU core voltage, when the board turns on (SMC reset/bypass)?
If yes, what is the voltage after 10-15s?
Also check USB activity, in this case.
Did you try known good BIOS?
 
CPUCORE_BOOT1: 4.8V
CPUCORE_BOOT2: 4.8v
CPUCORE_BOOT3: 4.8v
CPUCORE_BP1: 4.8v
CPUCORE_PHASE1: 0v
CPUCORE_PHASE2: 0v
CPUCORE_ISNS1_N: 0v
CPUCORE_SW1: 0v

There is USB Activity
I have not tried a known good bios yet
 

2informaticos

Administrator
Staff member
Impossible to get USB activity, without CPU core voltage.
Don't confuse USB power with activity!

If no CPU core, which other voltage appears on the board, when fans spin?
Check on all big coils.
 
The USB gets power but no communication/activity.

None of the big CPU coils get voltage on them

L7900: 1.2v
L8410: 3.3v
L7960: 0.95v
L8000: 1.0v

PPBUS_G3H: 11.34
PP3v3_sus: 3.29
PP3v3_G3H: 3.3
PP5V_S0: 5.1
 

2informaticos

Administrator
Staff member
Power good signals from the power supplies controlled by U7800 directly, are not routed externally.
So check presence of voltages from pages 71 & 72.
 
Took a second look over the board & noticed u8295 getting hot. Removed the chip and Pin 5&6 were short (PP3v3_s0_left)

Used an infrared camera and sent 1.8v through the line and it led to C2991(PP3v3_TBT_X_S0). Removed the Cap but short is still present.
 

2informaticos

Administrator
Staff member
You can inject until 3.5V without problems.
U2800 is the first suspect there.
Lift its metal shield to properly check if heats up.
 
U2800 was heating up after injecting 3V into the into Pin 5/6 on U8295

Replaced U2800 and everything is looking good. Thank you for the help.
 
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