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820-00875A Pulsing S5 rails

C

CRC2018

Member
Another liquid damaged macbook in today this one 820-00875A. Was a lot of liquid damage focussed around keyboard connector. Keyboard connector was burned and has been replaced. Board has been Ultrasonic'd for 4 minutes. The issue is the machine won't start, the S5 3.3V and 5V rails just pulse when charger is connected, PPBUS is stable at 13V and if a battery is attached it wont take power/charge. Charger negotiates correctly to 20v.

Seeing no activity on any S4 rails - i've checked 3.3v and 5v S4, S3 and S0 rails for shorts and found none.

PP1V_S5G is reading 105ohm to ground, it is also pulsing but voltage is not going very high (up to 0.1V or so)

I've checked all big coils on the board for shorts and also found nothing only L7410, L7420, L7430, L7210 and L7220 are showing 3ohm to ground and L7960 50ohm to ground but I think this is normal if someone could confirm.
 
2informaticos

2informaticos

Administrator
Staff member
Low values on CPU coils are likely normal.

1V_S5G rail is probably OK, as it goes to PCH.
You cannot detect peak pulse with DC voltmeter; o-scope can catch any fast peak pulse.

Atr you testing the board alone on the desk?
 
C

CRC2018

Member
Do not currently have a scope unfortunately - am checking rails with a Fluke meter. Yes board is being tested alone on desk without anything else attached other than a 85W Type C Charger.
 
2informaticos

2informaticos

Administrator
Staff member
Do you have any pulse at PM_SLP_S4/3_L?
Repeatedly trigger SMC_ONOFF_L and check for pulse at any of these signals; as S3/0 voltages too.

Don't forget page 64, be sure no short on any output.
 
C

CRC2018

Member
no pulses at PM_SLP_S4/3_L, no pulses on any S3 or S0 voltages either when triggering SMC_ON_OFF_L.
I'll check Page 64 again but I didn't see any shorts before.
 
C

CRC2018

Member
ok right i've gone through all the S5 rail feedback resistors and found R7910 was dead - have replaced and now board powers up. So that's one issue resolved.
Now issue #2 is the board works fine on the choose a boot device screen (option) but when I boot it up to either the customers SSD or my testing external HDD it'll boot then go to the login screen and then freeze very shortly after that then shut off after 30 seconds or so. Pressing the power button again makes it turn on once again but same behaviour.
 
C

CRC2018

Member
Ok i've tried a Windows 10 install USB - which boots fine and will sit on the welcome to windows screen for an hour no issue, no freezing no shutting down. Mac OS safe mode is also behaving the same as it does in normal mode = boots then shuts down shortly after hitting the login screen. Is this a possible ME issue? or OS X is looking for some sensor which isn't working maybe?
 
2informaticos

2informaticos

Administrator
Staff member
Could be ME region issue.
You can finish Windows installation and start to install all the drivers.
Then see if any driver causes shutdown the machine.
 
C

CRC2018

Member
Finished the windows install - works fine until drivers there - once windows update has run and installed drivers the machine again will freeze then shut off - just like it does after loading mac os.
I've been over the board carefully under the microscope and can see nothing else visible
 
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