MacBook Air 2014 battery will not charge

[ACS-Repair]

Hello All,
I have a unusual problem with a MacBook Air 2014 820-3437 that it will not charge the battery. I have 2 batteries that charge just fine in another 820-3437 so i assume that the batteries themselves are OK. One was new in 2020.

This board started off as a PP3v3_S5 short that was resolved (shorted capacitor) and came to life fine. While testing the computer I noticed that the battery was not charging so I checked the following components:

Current sensing:
R7121 10 ohm
R7122 10 ohm
R7151 2.2 ohm
R7152 0 ohm


plus:
R7100 0 ohm
R7101 4.7 ohm
R7105 20 ohm
R7115 252k
R7116 10k
R7142 993 ohm

These all measure to spec. I've replaced the ISL6259 and Q7155 both twice with no change.
The computer works fine on the adapter and with a charged battery, but will not recharge the battery.
When connected to the adapter, the voltage on the gate of Q7155 is 8.39 while the voltage on the source is 8.41. On a working board the gate drops to 0.6v to allow charging. on the defective board it drops to 0.6 to allow it to run on the battery. Voltage on the drain of Q7155 stays at the battery level 6.69v.
I'm using a genuine Apple 45w Magsafe 2 adapter for testing.

I'm scratching my head here as it doesn't make sense that this simple circuit should be working. i'll continue to plug away at it and i would appreciate it if anyone could suggest what i'm missing.

[mon2]

Re: MacBook Air 2014 battery will not charge

Measure the voltage to ground of the battery smbus lines (SCL and SDA).

Compare a working board and the non-working board. Check with the battery connected.

[reformatt]

Re: MacBook Air 2014 battery will not charge

Scope the SCL/SDA lines to the battery. Usually it's a bad SMC.

[ACS-Repair]

Re: MacBook Air 2014 battery will not charge

I did a check of the SCL and SDA bus with the battery connected and they are at 3.40v. I was afraid that it might be an SMC problem because everything else is fine. I will scope the lines to see if there is any activity.
I'm not able to replace an SMC with the tools that I have but I could try a reflow as a last ditch effort.

I put a scope on the SCL and SDA lines and I see a pulse about once per second on each line. This compares to the working board that I have. Not sure that this means the SMC is communication properly or not.

[ACS-Repair]

Re: MacBook Air 2014 battery will not charge

So, I did find something interesting.
I didn't report initially that I had to remove J9500, the connector for the LIO board. it was not connecting properly so I removed it and ordered a replacement, which is going to take a couple of weeks to arrive. it's always been in the back of my mind that it might mean something but I continued with testing the way it was.
I decided to replicate this test on my 2013 MBA with the IO cable disconnected from the logic board to verify one way or the other that it would have an effect. Strangely, that computer will also not charge the battery if the cable is disconnected. I'll need to research this a bit more because I don't understand what the connection between the two is.

In the mean time I'll let this sit until I can get the new connector attached and test it again.
Thank you all for your comments. your help, as always, is greatly appreciated!

[rookieme]

Re: MacBook Air 2014 battery will not charge

you're right
the macbook air needs good connection with the IO board in order to read the ac adapter and charge the battery

[reformatt]

Re: MacBook Air 2014 battery will not charge

The LIO flex has the one wire comms on it so it’s absence will disable charging. I’ve also had bad LIO boards cause no charging as well.

Under power tab in System Report, if battery data is present for cycles etc this indicates SCL lines are probably ok. Where I’ve had it bad is data is present but levels aren’t right. Last one I had the data low wasn’t going to zero.

[ACS-Repair]

Re: MacBook Air 2014 battery will not charge

Confirmed, after replacing the J9500 connector, the computer now charges the battery.
Unfortunately, I get high speed fan and heat pipe at 128 degrees. I always have trouble with these connectors but I believe it is on the board properly. I've swapped in a known good DCIN/LIO and flex cable but the problem persists. SMBUS_SMC_2_S3_SDA and SMBUS_SMC_2_S3_SCL have pulsing but don't appear to have any data. I don't know the full history on this board as it was recently dead.

[ACS-Repair]

Re: MacBook Air 2014 battery will not charge

I finally got this...
Turns out that R5370 on the SDA pull-up had gone open. Replaced the resistor and the heat pipes measure the correct value and the fan speed is normal.
Thanks to all that visited.