liquid damaged 820-00165-A with no fan, amber light OK, ALL_SYS_PWRGD = 1.2V

[joshAU]

Hi all.
Liquid damaged 820-00165-A
Minor corrosion on top side of board around U6100 - U1900 & U7701.
On the bottom, only a tiny bit near Q7155

Cleaned affected areas.
Get green then amber LED on magsafe2 adapter.
Tested with spare known good adapter
No fan spin.

I've tried to manually start it via shorting R5115/R5116, even though should turn on without battery when AC is connected.

It gets vaguely warm in two areas, around U2800 and around L6560, but not warm enough to isolate which component is causing it, or even which side of the board it is coming from.
No heat from CPU.

ALL_SYS_PWRGD is 1.2V

PM_SLP_S4_L = 3.32v

PP1V8_S3, PP5V_S3, PP1V2_S3, PP1V05_S0, PP5V_S0, PP3V3_S0, PP1V5_S0 all measure correct voltages.

PPBUS_G3H = 8.56V
PPVRTC_G3H = 3.3V
RTC_RESET_L = 3.3V
PCH_SRTCRST_L = 3.3V
PCH_INTVRMEN_L = 3.3V
PCH_DSWVRMEN_L = 3.3V
PP3V3_S5 = 3.3V
PM_DSW_PWRGD = 3.3V
PP3V3_SUS = 3.3V
PM_BATLOW_L = 3.3V
PM_RSMRST_L = 3.3V
PM_PWRBTN_L = 3.3V

Any help greatly appreciated.

 

[2informaticos]

Clean U1950 pads and resolder it.

Test the board without Q8150.
Check R8167 value.

 

[joshAU]

Hi again 2informaticos, and thanks for your help.

I cleaned U1950 and reflowed with flux - no change.
I then removed it - Pad 8 did look dirty, but after cleaning looked good.
I cleaned the pads, added some leaded solder, then resoldered U1950 - no change.

I removed Q8150 - no change.
R8167 = 10KΩ

 

[2informaticos]

PM_SLP_S3_L gets 3V steady?
If yes, start removing the resistors from ALL_SYS_PWRGD; one by one, keep R8167 in place.
Check when/if the signal goes high to 3V.
You may need to change U1950...

 

[joshAU]

Hi again.
Sorry for the delay.
I was away from work from last Thursday.

ALL_SYS_PWRGD is actually 0.12v, not 1.2V.

PM_SLP_S3_L is absolutely steady on 3.32v.

I removed r8164, R8165, R8166, r8168 one at a time, while leaving R8167 in place.
ALL_SYS_PWRGD still low (0.12v).

PM_SLP_S3_BUF_L reads 3.3v on pin 1 of R8167.

I replaced U1950 from another board - no change.
Sigh...

 

[2informaticos]

Something pulls down ALL_SYS_PWRGD.
If R8167 is good for sure, then should fine the culprit removin any components connect to ALL_SYS_PWRGD (one by one).
Each time you remove something, check the signal.
If still low, do not solder back removed components; just remove other more.
Start with Q8150, U1845 and continue with R8164/66/68.