820-00165 dead brain?

[jadao]

Hi all,

This is water damaged board.
Initially no Magsafe light, shorted pp3v42_g3h in SMC.
Replaced and we are back with green/orange light.

After Magsafe light there was no fan spin and no PM_SLP_S4_l, PMSYSRST_L was stuck at 0.50V but no short.
Decided it was time for a good bath, after ultrasonic fan spins once, it stops and then on again and stay on.

Is that normal on these 2015+ boards? I know the usual 830-3437 with 3 fan rtc cycles before it boot but not aware for these newer model...

All rails were present except PP3V_S4 witch is low (2,5V) but no short (4kohms to gnd, 0.355 in diode mode). I am not sur if this rail can prevent the board from booting, if I recall it used forr some peripheral wifi, bluetooth, Tbolt, trackpad...
Replaced U8000, but pp3v_s4 still low.

Here are some measures:
pp3v3_S4: 2,5V
cpu_VCORE 1,8V

PM_sysrst_L: 3.3V
PM_PCH_SYS_PWROK: 3.4V
PM_PCH_PWROK: 3.3V
PM_RSMRST_L: 3.3V
PM_BATLOW_L: present 3.3v
SMC_ADAPTER_EN: present 3.3V
PM_PWRBTN_L: present 3.3V
PLT_RESET_L: 3.3V
PPVRTC_G3H : 3,4v present at all places
RTC ic clock 32kHz yes

I have no red light on USB.
I replaced just in case the bios but nothing changed.

I am lost at this point about witch issue I should focus.
Thanks for any suggestion.

 

[jadao]

Ok I just tested with another 820-00165 and in fact it doesn't rtc cycles like 820-3435/37.
So my issue is:

1)PP3v3_s4 low 2,5V
2)It cycles once (i mean fan is on then off then on and stay on).

Not sure if 1) and 2) are related I am more concerned by 2).
Checked all 22 resistors and traces for spi rom and all is ok.

Out of desperation should I swap also U6101 and again ultrasonic?
Note I put back original U6100 as nothing happen when swaped.
thanks

 

[2informaticos]

PP3V3_S4_ comes out from U8000.
Does it get correct level for PP3V3_S5 and S4_PWR_EN?
You can bypass IN-OUT directly, just for test; see what happens.

To drop output from 3V3 to 2V5, U8000 should overheat, in case of external issue.
If not, maybe bad inputs (power, enable).

This board doesn't cycle at all when starts; if is OK, of course...

 

[jadao]

Yes, absolutely correct level at the inputs, PP3V3_S5 and S4_PWR_EN are both 3,4V.
This is why I conclude for bad chip but when replaced same thing...
I compared diode mode and it's the same with good board.
Thanks for the suggestion, iI will see what happen with bypassed 3v3 on in/out.
I will report back.

 

[jadao]

So I tied together 3v3 from input to output, and the voltage doesn't drop.
But the board is still cycling once and then stay on.
Any idea? Thanks

 

[2informaticos]

Do you get all secondary voltages?
All S3, S0 (pages 57/58), not only in the big coils...
VCORE tries to appear?

 

[JohnB8812]

This is one of those really shitty issues I’ve seen a few times and haven’t solved. I’m thinking it’s gotta be BIOS related, but I could be wrong. If VCore is definitely present, I’d say try another BIOS for testing

 

[2informaticos]

Don't forget to save backup.
I saw so many 00165 with corrupted BIOS...

 

[jadao]

2informaticos

Yes! all secondary voltages are present, will check them again in case something changed. The only tricky one was the PP3V3_S4 being 2,5V instead of 3,3v..
Vcore is present at flat 1.8V no adaptation no red light on the mouse.


JohnB8812

Thanks for the suggestion I've already tried another 820-00165 bios to discard any bios issue. But no change so I put back original Bios. At this desperate point I will try maybe to replace U6101 just to be 100% sure no bios issue.

Next thing I will try to reflow replace again SMC, I've already had a similar issue with 820-3437 macbook air was'nt cycling 3 times, instead it was doing the same: one cycle then stay on, reflowed smc corrected it.

Yep it's a shitty one...came back from far but probably not fixable, I will let you know thanks!

 

[jadao]

I stopped working on this board, first time I encounter this issue next time I will not spend that much time;(
Thanks for your help and sharing your experience.