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.

 

[Chuck60]

Ok I finally got back to this board. I don’t have ultrasonic I didn’t heaT anything as of yet. i replaced c8074, c8080 and some other parts. I’ve enclosed a image of the area they didn’t look quite right Cracks and loose. I plugged it in and fans spin normally
I powered it down and connect mouse and speaker had both cpu activity, chime. I tried to install in a chassis and now it won’t chime and it started 3 beeps I’ve tried cleaning the slot, ram and even different ram. Sooo im Stuck :

I measures around and vcore is around 1.04v but doesn’t drop down from there and at Pin 1 r5440 the voltage goes up to 500mv then drops to 99mv. Is this line supposed to be 1.5v? there’s no short here .620 diode mode and pp1v5_s3 is 1.5v stable. Fans spin full speed even though both cpu, gpu Thermal sensors are good. Lastly the Mouse no longer flashing quickly it just blinks every few seconds the after a minute the board shuts down. Check cpu/gpu for thermal paste and it fresh.

 

[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...