Recurring problem, blinking green magsafe, does not turn on.

[Sjenja]

So the powerails are ok. But when I look om =PPBUS_G3H or DCIN or any other rail, I see a strange recurring pulse. See picture attached of PP18V5_DCIN_CONN power rail. it is on 820-4924, but I have had this problem on other boards to 3115,2915 ect . Sometimes it solves it self, other times not, I have measured the current sensing resistors around U7100 (U7000) and they are up to spec. It does not seem like its the power rails it self that does this. Is this some kind of SMC thing or what is this ?
Could be nice if anyone else have had this problem to and knows how to solve it.

 

[dukefawks]

Is the board working? Was this liquid?

 

[Sjenja]

No, its not turning on. green light on the magsafe (blinking). It may have has some water damage but it has been ultrasoniced

 

[dukefawks]

What is happening at PPBUS_G3H and PP5V_S3?

 

[Sjenja]

same thing as on the picture. But they are there.

 

[dukefawks]

So it is power cycling. The usual suspects are clock chip, U1950 (on airs), resistors in SPI lines to ROM. Could also be 100 other things why it is doing that. 4924 many times have shorted CPU cause of liquid on CPU Vcore regulator.
Find the corrosion and you will find the problem.

 

[Sjenja]

Ok will take a look on the Clock signals and the SPI-ROM lines.