A1278 2012 820-3315 fan spins, no chime

[VinceLx]

Hello,
This board was water damaged.
- green light ok, fan spins (after a while fan spins high even with trackpad connected)
- no chime, no display, no USB activity with a mouse

PPBUS_G3H=12.3V
SMC_RESET_L=3.44V

SMC_PM_G2_EN=3.48V
PM_SLP_S5_L=3.31V
PM_SLP_S4_L=3.31V
PM_SLP_S3_L=3.3V
So it is running

ALL_SYS_PWRGD=3.31V
CPUIMVP_PGOOD=0V

R7402 and R7403 OK

What should I check next? Are the processor or U7400 dead?

 

[2informaticos]

Post exact voltage at L7510/20.
Do you note any drop on it, after 10-15s?

Check if all voltages from pages 71/72 are present.
What about PLT_RESET_L?

"PPBUS_G3H=12.3V"
This denotes communication problem between SMC and U7000.
Post voltage and diode mode to ground on SCL/SDA lines of battery bus.

 

[VinceLx]

Here are the values:
Voltage at L7510/20=0V
No fluctuations, it is stable 0V even after more than 15s

Voltages from pages 71/72 are ok

PLT_RESET_L=0V

SMBUS_SMC_5_G3_SCL=3.49V, on the scope I see a short pulse of square waves every second (0.53V in diode mode)
SMBUS_SMC_5_G3_SDA=3.49V stable, I can't see anything on the scope, according to a working board I should see also a short pulse of square waves every second (0.53V in diode mode)

I don't see a way to check the traces between SMC and U7000 without removing SMC.
How to proceed now? It seems indeed a communication problem between SMC and U7000?

 

[VinceLx]

Any idea on this?

 

[2informaticos]

Board cannot boot without VCORE.

R7974 is good?
Did you try known good BIOS?

 

[VinceLx]

Indeed R7974 is good, and I see 3.3V on both sides.
I flashed a known good BIOS, no luck this time...
So, next step is replacing U7000?

 

[2informaticos]

12.3V on PPBUS_G3H and missing VCORE should not be related.
You can fix PPBUS_G3H first, but this doesn't assure you that machine will start working after that.
If SMC is the culprit, then could be the reason...

 

[VinceLx]

I replaced U7000, exactly same behaviour: PPBUS_G3H=12.3V, and signals on SMBUS_SMC_5_G3_SCL and SMBUS_SMC_5_G3_SDA identical as before.
So I guess next step is SMC replacement, but this is not my level... so I have a donor board