A1706 MacBook 820-00923-A sudden death - missing vcore - 20V - 0.25A

[Crizz]

The Logicboard have no visible corrosion or burn marks.
The whole machine is clean.... I mean CLEAN! No dust in the fins!
I'm the first opened it.

No shorts on the coils!
All the S0-lines comes up except:
PPVCC_S0_CPU =0V 4.8Ohms tg
PPVCCGT_S0_CPU =0V 2.8Ohms tg
PPVCCSA_S0_CPU =0V 6.5Ohms tg

I get 20V / 0.25A on the Amp meter without battery.
I tried to boot in DFU-mode without success.

The power button works as i can turn the S0-rails on/off.
The heat sink gets slightly warm over time.

 

[2informaticos]

PPVCCGT_S0_CPU will only appear under graphics load, like playing YouTube videos.
PPVCCSA_S0_CPU must appear before VCORE (PPVCC_S0_CPU ).
All these voltages are controlled by U7100.

Check if you get correct voltages for U7100 and U7210/20/70.

Can be CPU problem, or BIOS corruption.

 

[Crizz]

OK as I said the optical inspection of U7100 and U7210/20/70 is witout any doubts.
I checked now all the VIN-pins, VCC-pins, EN-pin and pgood-pin....
All the pins have the voltage they should have.
I would like to learn more about the U7100-ic. It seams it is responsible for the vcore-lines and has a lot of other I/O lines.
Witch of these lines should I test next?
If this doesn't give me a hint, I will try to flash the BIOS tomorrow. I have allready a donor-BIOS and I have to clean the ME-region before flashing.

 

[2informaticos]

"I checked now all the VIN-pins, VCC-pins, EN-pin and pgood-pin....
All the pins have the voltage they should have. "
Do you mean to have voltage on all these pins?
I doubt to have high level on pgood of a missing output power rail...

 

[Crizz]

Yes I mean every pin has the right voltage.
I double checked it: U7100
CPUVR_PGOOD is indeed UP with 3.45V
CPU_VR_EN_R 3.35V
The PWM lines have 2.7V
None of the SENSE-lines have any voltage....

 

[2informaticos]

"CPUVR_PGOOD is indeed UP with 3.45V "
This indicates good VCORE, which is not present in your case.
It is only possible if bad solder on pin 47/U7100.
You can have more bad solders...

 

[Crizz]

I replaced U7100 with minor changes.....
PPVCCSA_S0_CPU came up = 1.1V
But PPVCC_S0_CPU =0V
And now CPUVR_PGOOD = 0V

Now I get 20V / 0.36Aon the amp meter....
How I get the vcore back?
Should I expect a dead CPU?
Or should I try my luck with flashing the BIOS?
______________________________________________________________

OK flashing the BIOS changed nothing!
I've another A1708 liquid damage that I fixed today and I compered ALL the pins of U7100:



The only big difference that I see is PIN 34.
But U7270 is working since PPVCCSA_S0_CPU is 1,1V
I don't know what else to check....
Is this a rabbit hole to hell???

 

[2informaticos]

"How I get the vcore back? "
You didn't have VCORE before.
"PPVCC_S0_CPU =0V "
Power good of U7100 was bad instead.

"
I replaced U7100 with minor changes.....
PPVCCSA_S0_CPU came up = 1.1V "
Not minor at all, you didn't have this voltage before.

"But PPVCC_S0_CPU =0V
And now CPUVR_PGOOD = 0V "
Power good signal is correct now, as you don't have VCORE.

Check R7120/23...

 

[Crizz]

R1720 R7120 are spot on 13,3K
But R7123 and R7124 are both 180K instead of 220K... I guess this is OK?

 

[2informaticos]

This could end in bad CPU...
You can try BIOS now, just for test.

 

[Crizz]

Finally I flashed the BIOS once again without any change.
So I have to stop further investigation due to lag of time and give it a NO-FIX here.