820-00840 / No boot / PP3V3_G3H Short to ground

[MisterAIL]

Hello everyone,

Firstly sorry for my english, french guy inside.

I brought a macbook pro A1708 - 820-00840 logic board, wasn't powering on.
History is a day, nothing happened when opening the laptop.

Nothing special inside, no corrosion, no liquid damage, never opened.

First, with the logicboard alone on the desk, mesures are :
5v017 and 0.000 amp. nothing else.
Finding a short on the PP3V3_G3H_VR, but not on the PP3V3_G3H (0.540 on diode mode), PPDCIN_G3H_CHGR_R present (5,1 volts) PPVIN_G3H_P3V3G3H around 4.1 volts. PM_EN_P3V3_G3H around 2 volts.

To isolate the CC, removed L6995. Short was not before it, but after, on PP3V3_G3H_VR. No short on PP3V3_G3H (at this time). Removed all caps C6996/5/7/8/C6988/9, but short still there.
Decided to remove the R6999. Then no short on PP3V3_G3H_VR (happy) but now PP3V3_G3H is shorted ! (around 0.002 on diode mode)

Replacing L6995, plug-in USB-C charger => 5v017 on charger, 0.00 amp, but PP3V3_GH3_VR present (3.42 Volts). Replacing R6999 (the real mistake?) but nothing else. No short on PP3V3_G3H_VR (Pin 1 of R6999) but sill present on pin 2. I suppose resistance can isolate a short, because nothing is connected to the ground.

Removing C7080 on PP3V3_G3H (the most easier before thinking at U7000) and... nothing more. I decided to leave the board beside.

This morning, i plug the charger to make new tests, and, without touching nothing since the last day, charge stays at 5v017 but amp drop from 0.3 to 1.8 ! Nasty smell around U3100 and U3200... touching in the zone and burning my finger on Cap C3100... Damned !

Charger pulling down to 0.6 amp and 4.7 volts on first usb-c port, stay around this values and, around 5v017 and 0,3 amp on other port...

So i decide to take the mesure of PM_EN_P3V3_G3H => 5,17 volts !! how it's possible !

I decided to remove C3100, C3200, and U7000. Unfortunatly there still a short on PP3V3_G3H, and another on the PP3V3_G3H_XPC_XA and XB. Not removed yet the R3000 and R3001 but i need your help before making more damage to the board...

A idea for the nexts steps (without more destruction?)

thanks a lot for your help

[mon2]

Re: 820-00840 / No boot / PP3V3_G3H Short to ground

Remove R3000 & R3001 - one at a time to see if the PP3V3_G3H short is removed.

PP3V3_G3H_XPC_XA and XB

I think you mean PP3V3_G3H_UPC_XA and XB.

Perhaps one or both of the ACE (U3100 / U3200) controllers got zapped.

[MisterAIL]

Re: 820-00840 / No boot / PP3V3_G3H Short to ground

I think you mean PP3V3_G3H_UPC_XA and XB.

Yes of course, excuse my mistake. It's lines PP3V3_G3H_UPC_XA & XB

So i remove the tinyyyyyy R3000 and 3001, one by one.

Short is gone on PP3V3_G3H_UPC_XA and XB, so i suppose U3000 & U3001 chips are fines.

But short on PP3V3_G3H is still there !

I remove R6999 to be sure again, but no difference...

With schematic, i'm a little bit confused what to test after that.

[mon2]

Re: 820-00840 / No boot / PP3V3_G3H Short to ground

You have a short on PP3V3_G3H somewhere on the board. With 0 ohms, appears to be a hard short where dead caps are often low resistance ohms but personally have not seen 0 ohms on a bad cap.

Remove the KEYBOARD cable and inspect the logic board keyboard connector with the meter to see if there is a possible short between pins 15 & 16.

PP3V3_G3H_KBD == PP3V3_G3H

Regardless, leave keyboard & R6999 out till the short is found.

[MisterAIL]

Re: 820-00840 / No boot / PP3V3_G3H Short to ground

Thanks for your reply mon2.

Board is alone on my desk since the beginning, nothing plugged on it.

Keyboard connector looks perfect, nothing special.

However, values are below :

Resistance from pin 15 to ground => around 2,6 ohms
Resistance from pin 16 to ground => around 0,9 ohms (same as shorting my multimeter)
Resistance from R6999 (pin 2) to ground => around 2,6 ohms

So Pins 15 & 16 aren't shorted together, connector seems fine.