820-00165 Boot to Apple Logo, shut down, restarts

[Neil250]

U3540 is severely corroded



PP3V3_S5: 3.3V at C3540
but bouncing at pin 1 U3540

Dry scraped away the corrosion, no alcohol, nothing at pin 1
Plugged it back in, boot looping stopped.
Damn thing booted right to desktop.

U3540 is wifi?

I may just replace this (but I don't want to unless I have to) vs. ultrasonic the board to clean it.
Could corrosion cause this behavior.
There is clock chip signal related to U3540.

This can't be that simple.

 

[2informaticos]

U3540 controls airport, is not a clock chip.
Is used to reset the airport card.
Also sends the clock request to PCH.

Machine works now, or still restarts?

 

[Neil250]

Restarts and boots to desktop.
I was even trying to install a fresh copy of Catalina but I think it may be shutting down 3/4 of the way through the install.
I'm not sure because it was an unattended install and when I came back it was at the old desktop. The new install did not proceed completely.


I am going to test some more but could a problem with the clock request to PCH cause the original issue.
I think it could.
It appears to be able to boot to desktop now.
Before I did the brief cleaning it was not even getting past the Apple logo.