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820-2936 - Doesn't start, S0 there, ALL_SYS_PWRGD missing

smiba

smiba

New member
Hey everyone another day, another issue

I have this 2936 board here where someone messed with before. I already fixed a area where their "put it full of flux and heat it up" procedure knocked an important pull-up resistor off.
Right now I managed to have all S0 power lines there, but I can't get ALL_SYS_PWRGD to become high

I've already replaced R7951 and R7952 as they did not mesure their right values, however the replacements do exactly the same which makes me think my multimeter can't calculate it properly as its a divider.


These are the values I measured, with the resistors I've written down their supposed values from the datasheet after the Part#:

Code: 
PP3V3_S0_VMON: 3.29V
R7951 (15k): 7.16k
R7952 (7.15k): 5.35k
VMON_3V3_DIV: 0.76V
R7933 (1k): 0.993k
VMON_Q2_BASE: 0.7V

PP3V3_S5_VMON: 3.30V
R7956 (150k): 148.7k
S0PGD_C: 0.13V

PP1V5_S3RS0_VMON: 1.48V
R7954 (1k): 0.995k
VMON_Q3_BASE: 0.78V

PP1V05_S0_VMON: 1.03V
R7955 (1k): 1.007k
VMON_Q4_BASE: 0.74V

R7957 (100): 99.6
S0PGD_BJT_GND_R: 0.109V

Between Q2&Q3 (Pin 8): 0.135V
Between Q3&Q4 (Pin 2): 0.127V

ALL_SYS_PWRGD: 0.049V

Any idea what could be it? It feels once again like the answer is right in front of my nose but I just can't quite put my finger on it.

Cheers!
 
Last edited:
smiba

smiba

New member
I checked R7962 - R7967 and they're all within specification

I mesured the value on pin 1 of each resistor (R7963 to 7966) and all of them expect PVCCSA_PGOOD returned 0.049V (PVCCSA_PGOOD was at 0.011V)
So I checked the U7100 chip and PPVCCSA_S0_REG_R was at 0V, I missed it it seems!

I checked if the enable signal and it was high and it was, also all the resistors come back within specification.

Decided to swap U7100, but still the same problem.

Where would you recommend looking? At this point I think the best would be to test continuity on VCCSAS0_DRVL, VCCSAS0_LL and VCCSAS0_DRH and maybe replace Q7100?
 
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