820-2850 fan spins for 10-15 seconds no cpu activity

[Chuck60]

Hi i have this board and I replaced a isl6259 which had a low PPBUS now I have 12.56v I found the I was missing PP1v05_S5 so I check u7600 area and all measurements where spot on I replaced u7600 and now the fan spins for 10-15 secs I went over the rails in diode mode and none are shorted :/ also no cpu activity with mouse And .859v at cpu. I removed heat sink think maybe no thermal paste but it was fine. All rails are fluctuating expect “PPBUS, PP5v_S5, PP3v3_S5” these 3 are stable. A tiny bit of water damage was on the isl6259 but that’s it. Here’s a video it’s weird because sometimes it’s spins longer than others.

 

[2informaticos]

Did you check if all power rails come on in these 10-15s?
Don't forget pages 71/72.

 

[Chuck60]

Yes I checked them while fan was spinning all voltages and seem normal for the few seconds of fan spin but abruptly get cut of :/ I will check those pages 71/72 thanks for your help

 

[2informaticos]

Also test it starting in SMC bypass mode.

 

[Chuck60]

Smc bypass does the same it doesn’t seem to respond to bypass

 

[2informaticos]

Try full known good BIOS.

 

[Chuck60]

I tried with a clean bios and it has the same issue

 

[2informaticos]

Board still turns off, if you remove DDR modules?

 

[Chuck60]

Yes with memory modules removed same issue. it seems that even though I get ALLSYSPWRGD it powers back down it’s like I loose all my enable signals at once

 

[2informaticos]

Heat BGA chips with quality flux.
Maybe be a problem caused by accumulated crap.
If still the same, pass the board through ultrasonic bath too.

 

[2informaticos]

Test the board alone on the desk again.
If works, then try connecting one device at a time and testing.

 

[Chuck60]

Yes I’ve done this it still does the same :/ with nothing connected just magesafe and also with just the battery.

 

[2informaticos]

Then some broken solders, or traces...