820-3330-B No power (Intermitent Green Light)

[javier_herart]

Hello

-No turning on.
-Customer found signs of corrosion and cleaned the board.
-Sometimes (1 of 10 times when I plug the PSU) I get green light for 2-3 seconds.
-Tried with another jack board and issue persisted.

Measurements with no Green light:
PP3V42_G3H: 3.4V
SMC_RESET_L: 3.37V
PPBUS_G3H: 12.50V
SMC_BC_ACOK: 3.26V
SMC_BC_ACOK_VCC: 3.40V
SYS_ONEWIRE: 3.40V
ADAPTER_SENSE:3.40V

Board takes 25mA from the PSU. Any idea? Thanks

 

[2informaticos]

Original 85W Magsafe charger?

I recommend to reball SMC.

 

[javier_herart]

Found a broken trace on U7201, fixed it and board turns on now.
But CPU voltages not present.

ALL_SYS_PWRGD: 3.3V

Could it be GPU related?

 

[2informaticos]

Check R7974 and R7402/03.

 

[javier_herart]

R7403 was open, replaced but same problem.

 

[javier_herart]

I noticed that on the U7400 side of the R7403/02 I got 12V but only for 1 second.
Replaced U7400 and same behaviour

 

[2informaticos]

TONA/B should drop to 0.5V approx, when CPU power supply works.
Be sure to have good solders and traces.
Also check all surrounding resistors and caps.
If all good, try known good BIOS.

 

[javier_herart]

Could you provide good Bios file?

 

[2informaticos]

Try this one.

A1286 820-3330-B_Clear me.rar

drive.google.com

Don't forget to check what I've mentioned about CPU power supply.