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820-00239 missing PPVCCEDRAM_S0_CPU

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cwalex

New member
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.
 
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cwalex

New member
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
 
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cwalex

New member
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.
 
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cwalex

New member
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
 
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cwalex

New member
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
 
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cwalex

New member
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.
 
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cwalex

New member
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

2informaticos

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

Use quality flux to reflow U7800; possibly crap under.
 
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cwalex

New member
No luck with the reflow. I have been reading the datasheet for SiC631 (U7410). The actual chip on the logic board is SiC635 but I can't find the datasheet for it and this one seems functionally the same. If I understand it correctly, the SiC chip (U7410 etc) needs communication from the controller (U7100) on the PWM pin. The signal tells it how and when to switch the built in mosfets. When I measure the voltage on the PWM pin of U7410 (pin1) I get 2.59V and it's just a straight DC signal. I double checked with the scope to see if there was a PWM signal and it's just a DC voltage.

I replaced U7410, U7420 and U7100 but it still has the exact same symptoms. I also checked that there is continuity between pin1 of U7410 and pin 25 of U7100. So my guess is that the 2.59V I'm reading on pin 1 U7410 is a result of the chip being put in tri-state mode by U7100. So where is the signal I'm missing that is causing U7100 to disable my missing voltage rails?
 
2informaticos

2informaticos

Administrator
Staff member
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.
 
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cwalex

New member
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?
 
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