820-2936 One wire ok, no power. Nothing past PP5v_SUS.

[gcain]

Customer board had a blown backlight fuse. Couple weeks later the board is back and not powering on at all.


PPBUS_G3H : 3.325
PP5v_S5: 5.02
PP5v_SUS: 0.431

C7841: 4.89v
R7842: 5.02

C7840:in1 5.02v
C7840:in2 4.89v

 

[larossmann]

PP5V_S5 is created by a chip that is powered by PPBUS_G3H - it steps down PPBUS_G3H's 12.6v to 5v.

PPBUS_G3H is 3.3v on your board. But you say PP5V_S5 is 5v.

?

 

[gcain]

Sorry, I miss read my notes!

PPBus_G3H is indeed 12.6
PP3v3_S5 is 3.325

I really need to tidy up my notes when I write them down.

 

[Repairable]

Pp3v3_s5 is 3.325 volts thats close inuf.
Keep going.
First s5 rails partly there.
Second s3 rails.
Third s0 rails.

 

[Gurmon]

what you getting on pin 6 U7940 ?

 

[gcain]

what you getting on pin 6 u7940 ?

u7940::1 = 3.323
u7940::3 = 0;
u7940::4 = 0;
u7940::5 = 3.323
u7940::6 = 0;


And Q5040:in1 == 0.640v.

 

[dukefawks]

The backlit fuse did not just pop for no reason. This must have been liquid spill. Corrosion under SMC/clock chip?

 

[gcain]

No evidence of liquid, but the board was pretty dusty so may have been humidity.

SMC area looks pretty clean and tidy.

 

[dukefawks]

Backlight fuse still good now? Could be a short in the LCD cable and that could short out BKL to any bus that is connected to the LCD. Check RTC stuff and shorts on all rails.

 

[gcain]

Backlight is OK now.

The system won't boot up and PP5v_SUS is around 0.430v.

 

[gcain]

dukefawks Any suggestions on where to measure from here?

I have a few of boards with missing PP5v_SUS now.

 

[dukefawks]

S5_PWRGD and PM_DSW_PWRGD present?

 

[gcain]

S5_pwrgd @ u7941::8 = 3.450

pm_dsw_pwrgd @ r1909::1 = 1.521

 

[dukefawks]

1.5V at DSW is no good. Usually SMC related, I bet there is crap under it.

 

[gcain]

Thanks Duke.
What are my options for sorting out the problem? I seem to get a large amount of SMC issues.

 

[dukefawks]

Reflow/pull and reball/replace another.