820-2936-b won't turn on (quarter fanspin)

[WeLoveApple]

Liquid damaged board had been worked on already. Possibly SMC reball and other repairs.
Current state:
Green light, all hot and S5 rails present.
SMC_BC_ACOK is present.
R7005, R7021/22, R7051/52 are fine.
Board is looping with quarter fanspin.

Any idea where to look?

 

[dukefawks]

Look for corrosion. Clock chip is a good suspect also R7402.

 

[WeLoveApple]

R7402 is fine. R2806 near clock chip was gone. Replaced that.
Clock chip was looking kind of okay, two pins were darker. I have no replacement from donor board so got it off and soldered it again.
U5410 was missing so put one on.
Nothing changed. Still repeated quarter fanspin.
Should I replace clock chip with a new one? Problem is I only could find some on air boards. Is there a chance that they will work?

 

[dukefawks]

Replace clock chip. It is on all boards 2011+
Also R2806 is no stuff, so should not be there.....

 

[WeLoveApple]

So by all 2011+ boards you mean macbook air boards too?

 

[dukefawks]

Uhm yeah, did you look at the schematic to see if they are the same?

 

[WeLoveApple]

Checked schematic of a 820-3437 board and clock chip looked identical so put it on this one.
This time it turns on but no chime.
CPU vcore is peresent.

 

[dukefawks]

USB mouse lighting up?

 

[WeLoveApple]

Nope, it is not.

 

[dukefawks]

Well that is bad. Could be anything, probably corrosion under SMC/PCH, but any corroded trace/resistor can cause this. Did you check without the RAM if it beeps? Speaker in the case must be connected, not the one on the board.

 

[WeLoveApple]

I tried. It doesn't beep.

 

[dukefawks]

No idea, could be anything. As I said, the clock chip was dead so there was liquid there. SMC is right there too, so maybe crap under it.