820-4924 Fan spin but no chime and no system load

[No-Clean]

Board came in with no power, clean board overall but some corrosion under U5580, that got fixed but still no power, raballed SMC, computer booted up once but keyboard and trackpad had some issues, keyboard only power button worked and trackpad only the click worked. After shutting down now the Mac gets fan spin but there is no chime and system doesn't load, the external USB activity light turns on but there is no blinking.

Any suggestions will be greatly appreciated.

 

[2informaticos]

Fan shouldn't spin at the begining, unless starts in SMC bypass mode.
Check SMC_ONOFF_L level, try disconnecting keyboard too.

 

[No-Clean]

Yes sorry forgot to mention that, fan spin starts when CPU gets hot, on this board I know this is normal, I did try without keyboard and also without keyboard and trackpad, same thing.

 

[No-Clean]

SMC_ONOFF_L is 3.4v steady

 

[2informaticos]

I said to check SMC_ONOFF_L thinking the board may start in SMC bypass, because of keyboard issue.
This will cause fan spinning at start.
Nex time, try to describe more exactly the symptoms...

Did you try SMC bypass mode?
Test the board alone on the desk; use only USB device for test.
Check all SPI Bus Series Termination resistors and all their traces.
Try known good BIOS, just in case; do NOT forget to make backup fiest!

 

[No-Clean]

SMC bypass nothing happens, SPI resistors good, I will hunt the BIOS and try, out of the time I invested on this one today it did start once but after that not any more, I looked for corrosion very slowly under max scope elsewhere and found nothing.

 

[No-Clean]

Found a couple good BIOS, tried both, same thing, at all times one thing that is steady is ppbus at 12.59v, I checked all power rails and not shorts found

 

[2informaticos]

Something more affected by corrosion.
Try to heat BGA chips with quality flux, then pass the board to UC.

 

[No-Clean]

Thanks a lot, I did as suggested, and same thing, board tries but no activity on external boot drive and of course no image.

 

[2informaticos]

So board stays on, with all volatges, but no activity?

 

[No-Clean]

Sorry customer was too intense on this board, gave it back at no charge of course.