Help Me diagnose A1706 820-00239 0.13v on PPBUS

[zipporobotics]

Hi everybody

trying to get data out of my MacBook Pro which I accidentally liquid damaged.

A Small drop of tea travelled on the back of the board nearby the trackpad connector: blowing it (see picture) digging a small hole in the motherboard (probably removed the first two layers.

https://imgur.com/a/TyHyyPm
Cleaned everything
Now trying to get this machine to boot again

Reading up a few post I've done some tests

Removed battery

A few measurements
- PPDCIN_G3H (19.95 V)
- PPBUS_G3H @ F7000, pin # 2 ( 0.13 V) (resistance to ground = 14 ohm)
- PP3V3_G3H (3.390 V)
- PPVIN_G3H_P3V3G3H (19.59 V)
- PPBUS_G3H @ D6902, pin # 1 (Missing, value 0.13 V)
- PPDCIN_G3H_CHGR @ D6902, pin # 2 (19.85 V)
- PPVBAT_G3H_CHGR_REG @ F7000, pin # 1 ( 0.13 V)
- SMBUS_SMC_5_G3_SDA (3.25V)
- TBA_VDDP (5 Volt)
- PPBUS_HS_CPU (0.13 v)

-L9400 both pin 11.05 K Resistance to ground
-Q7030 is getting 19.85 volt on pin 1-2-3
-Q7040 is getting 0.13 v on pin 1-2-3
-No voltage on L3500 and L8410
-0.13 volt measuring Q7030, L7030

couldn't find anything misplaced
how do I find if something is heating up without a thermocamera ?

Plugging in the USB C tester measures 19.99 volts and draws 0.067 amps

What should I test next ?

[mon2]

Re: Help Me diagnose A1706 820-00239 0.13v on PPBUS

PPBUS_G3H @ F7000, pin # 2 ( 0.13 V) (resistance to ground = 14 ohm)

Resistance is too low. Need to determine which side of the F7000 is responsible for this short condition.

Remove fuse F7000. With NO power, measure the resistance to ground of each side of the fuse pads (no fuse is installed).

Suspecting that the downstream (consumer side) is with the low resistance?

Power up again. Measure the voltage to ground of the PCB pad that is towards the ISL (regulator = SOURCE) side.

What is the voltage now of PPBUS_G3H without this load ?

[zipporobotics]

Re: Help Me diagnose A1706 820-00239 0.13v on PPBUS

Found the short

I removed F4500 and now I have 12.84 volts on PPBUS

Still
no signs of life

Now its drawing 0.13 amps at 20 volt
cpu is warming up


Further Check

I have no voltage on PPVCCSA_S0_CPU neither on PPVCC_S0_CPU

what should I check next ?

[mon2]

Re: Help Me diagnose A1706 820-00239 0.13v on PPBUS

Remove all power. Measure the resistance to ground of PPVCCSA_S0_CPU.

[zipporobotics]

Re: Help Me diagnose A1706 820-00239 0.13v on PPBUS

Hang ON
And thank you for patience as I'm re-learning power rails and I think I've found the correct order
So

PPBUS_G3H is ok at 12.98

Then I went on Measuring the PP5V_S5 rail and got 5 volt
So I went on the 3V3 Rail PP3V3_S5 and found it appears just a few seconds after plugging in the USB C and then its quickly cut off

Seeing its generated by U7650, nearby coil L7660, I measured the resistance to ground and got 7K. So it doesn't seem to be short neither it seems to be low

Could it be another stage being served by PP3V3 that has gone failed thus causing PP3V3 to shut down ?

I've noticed in the meantime U7900 and U7800 are getting really hot

and U7800 seems to be generating PP1V2_S3 which I suppose is the voltage needed for the cpu to turn on ?

Coil L7900 Measures 170 ohm to ground and PP1V2_S3 shows no voltage

Thinking about it, The tea drop (with a bit of honey) that travelled along the board, travelled through both U7900 and U7800. I have cleaned them around and superficially but I haven't yet tried spraying isoprophilic alcol under them.

Do you think I can try cleaning under them or should I just replace them ?

[zipporobotics]

Re: Help Me diagnose A1706 820-00239 0.13v on PPBUS

DID IT!

So I reflowed U7800

and the machine then booted again

Only issue

Fans are spinning at 6000 rpm

And Kernel Task is taking 254 % cpu


Could it be because trackpad isn't plugged in ?

Given I won't ever be able to plug in trackpad.
Is there a way to disable or tell SMC not to care about it ?

Already tried resetting Nvram Pram and SMC

No difference

[mon2]

Re: Help Me diagnose A1706 820-00239 0.13v on PPBUS

Attach the trackpad and test again. Be sure to also inspect the quality of the trackpad cable and that it is clean and well seated.