820-00239 missing PPVCCEDRAM_S0_CPU

[cwalex]

Hi,

This is a liquid damage board. The board turns on but does not POST. I have all the S0 rails except PPVCCGT_S0_CPU AND PPVCCEDRAM_S0_CPU. I'm struggling a bit to figure out how the voltage regulator circuits on these newer boards are supposed to work. Any help would be appreciated.

 

[2informaticos]

Check U7760/90 voltages.
Test for USB activity.

 

[cwalex]

U7760 Pin1: 5V, all other pins 0V
U7790 pin6: 1V, all other pins 0V

 

[2informaticos]

PPVCCEDRAM_S0_REG_F should be present at pin 5 of U7760.
Did you check it at L7700?

 

[cwalex]

Apologies, I just double checked my readings. I get 1.05V at L7700 and at pin5 of U7760.
Corrected: U7760 Pin1: 5V, pin5: 1.05V, all other pins 0V

 

[2informaticos]

Where was the spill?
Check for short on missing power rails.

 

[cwalex]

68R to gnd on PPVCCEDRAM_S0_CPU
5.8R to gnd on PPVCCGT_S0_CPU

The spill was at C7837. Had to run a jumper from pin1 C7837 to pin1 C7838. Replaced C8000 and C7962.

 

[2informaticos]

Check signals for U7800/(1 of 10).

 

[cwalex]

Pmic_shutdown_l = 3.3v
pm_slp_s0_l = 3.08v
s5_pwrgd = 3.3v
p5vs4_pgood = 3.3v
pm_slp_s3_l = 3.3v
p1v8sus_pgood = 3.3v
pm_slp_s4_l = 3.3v
pm_slp_sus_l = 3.3v
cpuvr_pgood = 3.3v
pm_slp_s0_l = 0v

 

[2informaticos]

"pm_slp_s0_l = 3.08v
-----------------------
pm_slp_s0_l = 0v"
Strange, no?

 

[cwalex]

Wow, sorry again. I'm sure that was my mistake. I have just taken all the readings again.

PMIC_SHUTDOWN_L = 3.27V
PM_SLP_S0_L = 3.08V
S5_PWRGD = 3.32V
P5VS4_PGOOD = 3.32V
PM_SLP_S3_L = 3.35V
P1V8SUS_PGOOD = 3.29V
PM_SLP_S4_L = 3.35V
PM_SLP_SUS_L = 3.35V
CPUVR_PGOOD = 3.31V

 

[cwalex]

Got an update. PP5V_S0 is missing from pin 29 of U7410 and the other phases of my missing rails. There is a 0.2R short to gnd on that line. Now I just have to figure out where the short is.

 

[cwalex]

Scratch that. The boardview for this model is screwed up on those sic chips so I was counting the pins manually. I didn't realise that a pin is skipped on the bottom edge so I had the wrong pin which was gnd Looking at the datasheet for the sic631 since I can't find the datasheet for the 635 on my board.

 

[2informaticos]

If board stays on, you cannot have short on 5V_S0...

Use quality flux to reflow U7800; possibly crap under.

 

[cwalex]

Cheers, there is no short I was probing the wrong pin. I'll reflow U7800 with some amtech.

 

[2informaticos]

Enabling graphics cores is not so simple.
PCH, CPU and BIOS are involved.
As you miss other voltage, GTx will not come on.
I supposed to be the last voltage which appears on the board.

 

[cwalex]

Do you mean PPVCCGT_S0_CPU is the last voltage to appear? I suppose I could try flashing an EFI dump if I can find one. Can you think of anything else to try?