820-01987 - pulsing PP3V3_G3H

dudipupan

Member
Hello everybody :)

I'm currently working on a MBP (820-01987) with some corrosion around C6406 with pulsing PP3V3_G3H.
It is taking 20V and pulsing 15mA to 22mA.

I don't see any obvios liquid damage on U7650, but I think this could cause the pulsing PP3V3_G3H? It's pretty close to C6406 and could be damaged too?

I am a bit cautious since it is a very new device - so I prefer to ask here first :)
Best regars

Lucas
 

dudipupan

Member
I have the correct schematic - just missing boardview. But there is a illustration of the components in the schematic.
 

dudipupan

Member
Oh sorry, didn't understand that you need the schematic :-D Thought you were just asking if I'm using the right one ;-)

Uploaded it here
 

2informaticos

Administrator
Staff member
Steady 20V at USB input?

Check for short on all big coils.
Be sure all solders and traces around U7650 are good.
 

dudipupan

Member
Yes I'm getting steady 20V at USB input (according to my USB-C amp-meter).

Resistance to Ground on the big coils:
L7270: 4.2 Ω,
L7210: 0.6 Ω,
L7220: 0.6 Ω,
L7410: 0.8 Ω
L7420: 0.8 Ω,
L7702: 41.5 Ω,
L8102: 130.5 Ω,
L8100: 0.295 kΩ,
L7030: 365 kΩ,
L7690: 1.9 kΩ,
L7670: 23 Ω,
L8410: 1.11 MΩ,
 

2informaticos

Administrator
Staff member
"L7210: 0.6 Ω,
L7220: 0.6 Ω,
L7410: 0.8 Ω
L7420: 0.8 Ω"
Looks like shorted CPU.
To be sure, lift all these coil one side and see where the shorts remain.
 

dudipupan

Member
The shorts remain on the CPU (PPVCC/GT) side (pin 2) on all of the 4 coils.
Just injected 1.5V on pin 2 of coil L7210 - the CPU took 3 apms, getting warm but not as hot (especially not locally hot) like the other CPU shorts occured on other boards i had for repair in the last months.

I'm still struggling in rating if a resistance of the CPU core is good or not(if it's not 0 or 0.1 Ω :D)
 

2informaticos

Administrator
Staff member
The resistance should be bit higher than 1 ohm.
If you have 0.6 ohm, multimeter leads have 0.3 ohm probably.
So CPU itself remains with 0.3 ohm...
 

dudipupan

Member
Hmm okay :-( Maybe just don't want to admit that it's another dead CPU :D That was the diagnosis of my last 5 boards.
Sould the pulsing of the PP3V3_G3H stop with removed coils?
 

dudipupan

Member
I just measured the resistance of the CPU a friends Macbook Pro from 2019. Odlly he had nearly the same CPU resistance (0.9 Ω and 0.8 Ω) on the coils. So maybe there is still some hope for the MBP?
 

piernov

Moderator
Staff member
As a reminder resistance to ground must be measured when board/CPU is dead cold and all power drained from it.
 

dudipupan

Member
That's what I did :) Battery disconnected, board was completely cold, left the probes very long for the measurement to be sure it is completely discharged :)
 
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