820-00840-a Pulsing PP5v_s4

DoubleGrinder

New member
Hello, I have a board that had previous water damage that is pulsing PP5v_s4.

I can eliminate the pulsing of PP5v_s4 when I remove R7192, when this resistor is removed I get:

PP5v_s4: 5.014v
CPUVR_VCC: 1.6v

It seems when this resistor is put back into place PP5v_s4 begins pulsing again.

I have tried replacing U7100 twice with the same result of 1.6v on CPUVR_VCC and subsequent pulsing on PP5v_S4

I also tried replacing U7650 before I discovered the issue is pertaining to the connection point at R7192

When R7192 is removed I get:

USB-c Ammeter: 20v,0.05A
PP5v_s0: 5.115v
PP3v_s0: 3.3v
ALL_SYS_PWRGD: 3.2v
PPVCCCPU_S0G: 0v
PPbus_G3h_CPU: 13.03v

When R7192 is on the board I get:

USB-C Ammeter: 20v, 0.01-0.09A pulsing
PP5v_s5: 5.2v
PP5v_s4: 0.0-3.1v pulsing
ALL_SYS_PWRGD: 0V
PPVCCCPU_S0G: 0V
PPBUS_G3H_CPU: 13.03V

I'm not really sure what the next steps are, I'm confused on why CPUVR_VCC is at 1.6v as I believe the joining of the 1.6v and 5.1v from PP5v_s4 at R7192 is causing U7650 to pulse but I can't find any reason why CPUVR_VCC is at 1.6v on it's own
 

2informaticos

Administrator
Staff member
First of all, welcome to the forum!

Which areas have been affected by liquid spill?

Post exact ohm resistance to ground at L7210, L7370, L7410.
Also at C7102.
 

DoubleGrinder

New member
Thank you! After being a long-time lurker I'm excited to join the club!

Areas affected by the spill were USBC area from C6405 down to U8400, no liquid damage was actually on J3300 or U2800 , just around the rough area of that side of the board

Ohm to ground:

L7210: 8ohm
L7370: 12.1ohm
L7410: 4 ohm
C7102: 53 kohm
 

2informaticos

Administrator
Staff member
So liquid spill into backlight area, bad news.

CPU may be damaged now, because of leakage between backlight output and data lines.
Seems that board restarts when CPU power supply tries to work.
Check what happens in SMC bypass mode.

R7101 has correct ohm value?

If you can't find another corroded component, or broken trace, then bad CPU.
Just in case, test the board alone on the desk; nothing connected, apart of charger.
 

DoubleGrinder

New member
That's quite unfortunate,

My J4810 connector hinge broke so am currently waiting on a replacement to arrive soon before I can test SMC Bypass,

R7101 is at 53k ohm

I'll keep looking for another corroded component/trace, but as of now looks pretty bleak.

when board is tested alone, nothing connected I got similar ammeter reading of 20v, 0.02-0.13 amp pulsing.
 

DoubleGrinder

New member
I will also mention, this board did work after initial repair, when it first arrived it had a short on PPBUS_G3h which was repaired by removing and soldering on a new C6424
 

2informaticos

Administrator
Staff member
"R7101 is at 53k ohm"
In schematic, appears to be 10 ohm.

You don't need TP/KB for SMC bypass.
Use SW9988/89 pads, instead of power button.
 

DoubleGrinder

New member
Ah my apologies 2informaticos,

I misunderstood, R7101 is 10.9ohm measured, I measured it to ground the first time.

Also after connecting the two pads for SW9988 and plugging in the charger, device pulls 20v and pulsing 0.02-0.09 amps.
 

DoubleGrinder

New member
So I tested it after waiting 10 seconds with the two pads connected and still had the same result of pulsing amperage from 0.02-0.09ish amps, Still having pp5v_s4 pulsing as well
 

DoubleGrinder

New member
Hey 2informaticos,

I swapped BIOS chips between my working (without USB devices) MacBook and my non-working MacBook, looks like the BIOS chips are fine, the non-working machine is still remaining to have pulsing amperage between 0.02-0.09 amps at the ammeter,

looks like it might be water damage unless I can miraculously find an issue in the next coming weeks
 

2informaticos

Administrator
Staff member
Put back the SPI chip on the other board.
You don't need ME issues on that.

In this corroded board, if you can't find anything else affected by liquid, I bet for damaged CPU...
 

DoubleGrinder

New member
I have an update for this board, I decided to last-ditch effort toss the board into a reflow oven to see if maybe there was a poor solder connection somewhere that was causing the issue, when I pulled it out it was taking 20.3v 0.18-0.20amp. The device does cause fan spin for about 5-6 seconds before fan stops, this usually coincides with the amps going from 0.18-0.20amp to 0.04 amp, then back up to 0.18-0.20amp


The board is getting all S0 rails
and the board is getting PPBUS_G3H_CPU at 13v
L7210/20 are at 0v and PPVCCCPU_S0G is at 0v

Does this still sound like dead CPU or should I attempt to replace U7210/20 to try to get power to L7210/20?
 

2informaticos

Administrator
Staff member
CPU core voltage depends by PCH/CPU, but BIOS is also involved.
This voltage requires more than a simple enable signal.
 

DoubleGrinder

New member
Okay, I'll attempt a few different repairs, as of right now it sounds like it's worth while to test out new BIOS, and replace U7210/20 to see if I can get voltage on PPVCCCPU_S0G
 
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