Macbook Air 820-3437 works again but PPBUS_GH3 too low


Hi there,
I am glad to be a member of this community and here is my first post :)

I managed to fix a 820-3437 Board by removing a short to ground on PP3V42.
I had to replace some Caps getting very hot when I was injecting 3.4V with my bench power supply.

Furthermore i had to replace the Con-Board flex cable. The pins where burned to dust!

After all that the fan went on - off - on - off - on - off - on and finally it remains on and everything seems to work and my work were done right? Not really :)

ASD reports PPBUS is too low and I measure 7.6V on the whole rail. I don´t think something is shorting to ground since nothing gets really hot.
Furthermore all the resistors in the ISL6259 area measure good values...

So what did you think about this problem?
Should I follow the rabbit or leave the machine as is?

--> The customer has his machine already back for data backup since the machine works and he knows about the issue and he will report unusual behavior.


7.6V is fine with a battery that is not fully charged. You should have checked the actual value in ASD. Problem is probably around Q5500, R5501/02. The machine will work slow


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Thank You for the reply
Q5500 was the first place i looked at - I forgot to mention it
Everything measures and looks fine

I attached a picture so you don't need to search it your self
PPBUS_G3H on the left side is already 7.6V so the outgoing signal on PIN 3 is also 7.6V

The outgoing signal SMC_PBUS_VSENSE on the right side is created from PIN3 of Q5500 and the voltage divider R5503/ R5504 - all measures fine
So for me this section was OK and I went on.

My guess is there is no sensor issue but the real value of PBUS is/was indeed too low!
Which raises the question on why PBUS is/was too low?

Maybe you're right and 7.6V is fine for a not fully charged battery and I will run ASD with a charged battery again when I get my hands on it!

I will report back



You can check in ASD the actual value that is being measured. It will be a lot lower than 7.6V before it reports an issue. Run EFI ASD and check under hardware profile.