MacBook Pro 2017 A1706 820-00923 no power, low voltage PPBUS_G3H

[Tennen]

Heya, so recently a MacBook Pro 2017 A1706 820-00923 reached my table, showing no signs of life at all. I am trying to use it as an opportunity to get more into the details of fixing Apple products. What I did so far might not have been ideal, but I am trying to improve.

The story I got told:
The MacBook received a new battery at some point and later at a random point in time just stopped working. Some specialist shop tried to diagnose the issue but only tried another battery - concluded mainboard damage and returned it to the customer.

What I did and learned so far:
Visually it looks fine for the most part. The occasional solder ball or a minute amount of white debris do not really look like the issue.
U8200 got warm very quickly when powered from a 5 Volt power source (into a USB-C port on the mainboard). Measuring PP3V3_S5 to ground looked like a short (0 Ohms) to me. I desoldered U8200 to take it out of the equation, but nothing really changed. Wrong order of actions I suppose, but here we are.
The mainboard draws 1.5 Amps at 5 Volts. The CPU heats up slowly on 5 Volts, but gets hot very quickly with a 20V PD-supply. I did not notice it at first, because at 5V 1.5A the heatsink did a great job of passively cooling it down.

Voltages:

PP3V3_G3H 3.42V
PPVIN_G3H_P3V3G3H 4.63V
PPBUS_G3H @ D6902, pin # 1 4.25V
PPDCIN_G3H_CHGR @ D6902, pin # 2 4.92V (Powerbank, 5V)
PPBUS_G3H @ F7000, pin # 2 4.25V
PPVBAT_G3H_CHGR_REG @ F7000, pin # 1 4.25V
PPDCIN_G3H 4.93V (Powerbank, 5V)
Q7030 1/2/3 4.92V
PPBUS_HS_CPU 4.22V

Mosfets:
Resistance between:

1. source & drain
2. source & gate
3. gate & drain

Q7030:

1.1 630kΩ S1/D2-D1
1.2 -200kΩ S2-D1 going up
1.3 2000kΩ S2-S1/D2 going up
2.1 inf S1/D2-G2
2.2 1960kΩ S2-G2
2.3 2000kΩ S2-G1 going up
2.4 0kΩ S1/D2-G1
3.1 1920kΩ Ohm D1-G1 going up
3.2 0kΩ S1/D2-G1
3.3 2000kΩ D1-G2 going up
3.4 inf S1/D2-G2

Q7040:

1.1 50kΩ S1/D2-D1 going up slowly
1.2 -374kΩ S2-D1
1.3 555kΩ S2-S1/D2
2.1 1910kΩ S1/D2-G1
2.2 inf S1/D2-G2
2.3 inf S2-G1
2.4 1920kΩ S2-G2
3.1 inf D1-G1
3.2 inf D1-G2
3.3 1910kΩ S1/D2-G1
3.4 inf S1/D2-G2

I am suspecting a failure of the Mosfets or something in that direction, but I lack the experience to know where to look exactly and which conclusions to draw. The CPU might be gone for good, given it's intermediate role as a space heater (which . But I would still like to try to fix the rest and see for myself.
Any directions would be insanely helpful!

[mon2]

Re: MacBook Pro 2017 A1706 820-00923 no power, low voltage PPBUS_G3H

1) PPBUS_G3H is low. There must be an excessive load on this rail.

2) remove all power, check the resistance to ground on both sides of F7000 fuse.

3) remove F7000 and power up again. What is the voltage on the smd pads before F7000 ? Is it now higher?

[reformatt]

Re: MacBook Pro 2017 A1706 820-00923 no power, low voltage PPBUS_G3H

Sounds like you aren't getting 20V negotiated via USB-C. CPU/PCH getting warm in that condition does not sound great so don't get your hopes up.

Look for corroded caps on the extreme edges of the board, in addition to the circular bits where the fans are. A shorted sub-rail will result in a dead board and no 20V.

These boards are badly designed with the CPU VRM driver IC and DRMOS IC's at the top edge of the board. They are the first to be hit when you get liquid spillage and it's often fatal. Check for resistances around each rail for the CPU and PCH before you invest too much time into it. U7270, U7210, U7220 are the main ones.

[MobileXT]

Re: MacBook Pro 2017 A1706 820-00923 no power, low voltage PPBUS_G3H

Do you have a USB-C meter? look like you only having 5V on the DC-in. Check one of the CD3215 it could be bad or shorted.

[kurland]

Re: MacBook Pro 2017 A1706 820-00923 no power, low voltage PPBUS_G3H

I don't see how Q7030/40 could have anything to do with it, your problem is 0 ohm on PP3V3_S5, which goes directly to CPU and loads of other places.

When you removed U8200, is resistance to ground still 0ohm? If so it's likely the CPU if that is getting hot (although that doesn't explain why U8200 got hot)
If you have an infrared camera you would see a short within the CPU starting as a concentrated spot, whereas a more uniform spread of heat is normal. You may also use Zippo lighter fuel like Zorin in this video

How to spot a failed CPU