820-00840-A Power Issue

outta-warranty

New member
Hi!

I would like to ask for assistance in a 820-00840-A board. I'm more like into iPhone repair but I had some success in older Macbook repairs. This is not a customer board, it is for me to entertain myself in this hard covid times...

I think I found a rabbit hole but I would like to ask for some guidance, and please be very clear and lucid with me, also with patience. Thank you.

HIstory: It is water damaged.
C7748 was shorted so I removed it.

ppbus_g3h_cpu steady 13.05V
ppbus_g3h steady 13.05V
pp3v3_s0 0V .170 in diode mode
pm_en_p3v3s0 0V

From the power supply:
19.9V
0.04-0.06A
0.03-0.08A

Where should I look next?

Thank you for your time.
 

2informaticos

Administrator
Staff member
Any liquid sign around U7650?
Post diode mode to ground at L7670/90.
Also post U7650 voltages; pins 23, 12, 13, 22, 29, 21.
 

outta-warranty

New member
Hi!

Sign of liquid around U7650

L7670 is .416
L7690 is .001

pin12:0V
pin13:0V
pin21: 0V
pin22: 3.3V
pin23: around 0.5V
pin29: 0V

Edit:
Looks like the pin23 is damaged by corrosion. There is 13.05V on c7650 capacitor.
Also the PP3v3_S5 rail is shorted.
 
Last edited:

2informaticos

Administrator
Staff member
U7650 is still connect there.
If looks ugly, you can remove it and check again.
If short goes off, is yuor lucky day.
Be aware, do NOT power up the board without U7650, under any reason!!!

Is more probably to have the short in other point.
Ohm value is low enough to heat something injecting voltage.
Start with 1V and do not go higher than 4V.
Let PSU current limit to max and remove CPU heatsink.
 

outta-warranty

New member
Hi!

I tried to locate the short but I can't find which one is. It is somewhere around C8233 where the heat comes from. I tried to use the alcohol method and the thermal camera method but the whole area is heating up. Also the CPU is getting hot by the time because that is on the other side.

I checked and there is a short to ground on the PP1V_S5G as well.
 

2informaticos

Administrator
Staff member
Central die is for CPU core, smaller one close to big coils is iGPU and the other is PCH.
Does PCH die overheats?
 
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