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820-3115 No Power, S0 rails present, No Power.

S

SMMRepair

Member
I have an 820-3115 board that has no power and is really confusing me. It had no liquid damage, but won't power on. Green light is good. S0 rails are present. I can "hear" the CPU working/on (high pitched noise with very subtle "tick" noises, etc), but I get no fan. My pp3v42_g3h is high (3.58v). The fan twitches ever so slightly when charger is connected, but nothing more (no cycling of twitches, just one lone twitch then done).

ppbus_g3h: 12.58v
ppbus_s5_hs_computing_isns: 12.55v
ppbus_s5_hs_other_isns: 12.56v
ppdcin_g3h: 16.78v
pp3v42_g3h: 3.58v (high)
ppvrtc_g3h: 3.3v
pp3v3_s5: 3.34v
pp5v_s5: 5.01v
pp1v05_s0: 1.05v
pp3v3_s0: 3.31v
pp5v_s0: 5.01v
PP1V8_S0: 1.80v
PP1V5_S0: 1.5v
PP1V05_S0_PCH: 1.05v

Any ideas?
 
S

SMMRepair

Member
ALL_SYS_PWRGD is not present, no (0v).

After looking at the board a bit more, I think the high pitched whine may be a stuck transistor somewhere and not the CPU being on. The CPU gets slightly warm after a minute or so, but not hot with activity.
 
S

SMMRepair

Member
OK, rechecking some rails, I now do NOT have PP1V05_S0_PCH. I did at one point, I'm sure of it. Going to go through the power block diagram again and see what's up.
 
S

SMMRepair

Member
OK, I have a more fruitful update.

Following the block diagram, my measurements fall off after steps 21:

21: CPUVCCIOS0_EN is 3.25v @ pin 1 of R7981 and at pin 3 of U7600.
1V05_S0_LDO_EN 3.25v at pin 1 of U7780.

22: CPUVCCIOS0_PGOOD is 0V (Pin 9 of U7600)

I get a good 5.08v on pins 13 and 14 of U7600, so it's being powered and it has voltage on the enable pin. I replaced U7600 and no change (still 0v on pin 9), so it's missing some inputs. Here are my readings for U7600:

pin 1: 0v
2: .2v
3: 3.25v
4: .5v
5: 0v
6: .5v
7: 1.02v
8: 1.045v
9: .05v
10: 1.05v
11: 1.13v
12: 5.6v
13: 5.08v
14: 5.08v
15: .954v
16: 0v

Any help appreciated on where to go from here.
 
D

dukefawks

Administrator
Uhm you have 1.05V on pin 10, this means U7600 is working fine......PGOOD is pulled down by another rail regulator.
 
D

dukefawks

Administrator
Look at the diagram and see which regulators are connected to ALL_SYS_PWRGD. One of them will be missing. My bet is on PVCCSA or 1V8S0
 
S

SMMRepair

Member
This board is confusing the shit out of me. I don't understand what type of failure I'm looking at (I've been working on boards for 6 months); all of my regulators (CPUIMVP_AXG_PGOOD, P1V8S0_PGOOD, P5V3V3_PGOOD, CPUVCCIOS0_PGOOD, and PVCCSA_PGOOD) are measuring .05v, when they should be 3.3v. At R7967, I get 3.3v on pin 1 and .05v on pin 2 (of course). Resistor measures good. Diode mode reading is within 5% of a known-good board.

All of these regulators seem to be created in different areas (U7400, U7760, U7200, U7600, U7100). I've replaced U7600, U7200, U7100, and the others seem to be working fine. Enables and power voltages to each IC seem fine. For example, I have my enables and vin for U7200 (compared to a good board, the measurements are the same), but I get 0v at pin 23 of U7200 (my p5v3v3_pgood). What could be making all of these regulators stay low? I don't detect any shorts or weird things via diode mode compared to a working board.

I'll be sending this one off to be repaired unless you guys have any other ideas. Thanks!
 
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aprendiz

Moderator
Remove one by one R7966, R7965, R7964,R7963 and R7962..... Remove one resistor and check ALL_SYS_PWRGD signal, no present?? put back the resistor, remove other resistor and try again....
 
S

SMMRepair

Member
Thanks, guys. Aprendiz, I did as you said, but ALL_SYS_PWRGD signal never showed up. I'm going to call this one a fail and send it on for repair by more experienced hands! :)

Thanks guys. I appreciate all the help as usual. :)
 
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