Macbook air 13 820-3209-a dead

[sdogs]

Hello guys ;-)
I have a macbook air 13 in my hands that shows no sign of life, logic 820-3209-a
I tested with bench power supply and it has no current draw.
I have noticed some signs of corrosion and a blown capacitor (c7022), I have replaced and rebuilt the damaged track but nothing has changed. I realized that by measuring in diode mode on pin 23 of the U7000 (replaced) I have a measurement of 0.10 ohm.
With power supply connected and without battery I have the following voltages
PPBUS_G3H is about 1.53v
PP3V42 present and stable at 3.42v
PP18V5_DCIN_CONN 16.5v

I noticed a strange thing by removing q7030 at pin 1 with diode measurement I have a good value about 0.80 ohm and also at pin 23 of the U7000, so I replaced it but the situation returns to the starting point.

Very slight sign of corrosion near the SMC chip but it doesn't seem to be affected.
I'm stuck.....any suggestions?

[reformatt]

Re: Macbook air 13 820-3209-a dead

Measure on L7030 to ground in resistance mode. It's low ohms?

[sdogs]

Re: Macbook air 13 820-3209-a dead

yes, I tried to measure both with L7030 connected and disconnected and in both cases pin 1 is very low.
when disconnected at pin 2 the value is normal

[sdogs]

Re: Macbook air 13 820-3209-a dead

I'm sorry in the previous post I answered by measuring diode mode, resistance mode rising value about 100 ohm

[reformatt]

Re: Macbook air 13 820-3209-a dead

Sounds like corrosion around the ISL? Use the boardview to check all damaged traces are continuous for R7021/R7022 to pins 27/28.

100 ohms is too low so something not right there. Check your patch job and soldering of U7000/Q7030.

[sdogs]

Re: Macbook air 13 820-3209-a dead

i am really freaking out, i checked R7021/R7022 and there is continuity.
with measurement in diode mode with Q7030 disconnected at pin 7 I have about 0.80 ohm if I put it back it goes down to 0.10 ohm, obviously the same thing at pin 2 of the c7025 which is connected to pin 23 of the U7000.
The value remains low even with u7000 disconnected from the pcb....
I tried to connect c7025 but the problem remains.
I don't think there are any other signs of corrosion, I would like to avoid heating SMC....what should I do?

[mon2]

Re: Macbook air 13 820-3209-a dead

1) Don't freak out. We have Chic for that..

https://youtu.be/0ABl4YwnWjg

2) R7021 / R7022 are expected to be low resistance resistors @ 10 ohms each (10R). This means that in diode mode, the meter will tone beep as the resistance is much like a short condition to the meter. That is, a low resistance of 50 ohms (estimated) or lower will show as 'continuity'.

By design, these resistors must be a low value.

3) Remove all power, meter in the lowest scale.

One meter probe across R7021. Other meter probe on the other side of R7021.

What is the measurement? It should be ~10 ohms. Confirm it.

Repeat for R7022.

[sdogs]

Re: Macbook air 13 820-3209-a dead

I confirm, value R7021 10 ohm
I realized that R7022 is missing .....
I have other recovery logic, not exactly the same, but in these it is present

[mon2]

Re: Macbook air 13 820-3209-a dead

Good. Also confirm R7022. It should be the same value. These are 1% tolerant parts so should be 10 ohms again.

Update - see next post.

[mon2]

Re: Macbook air 13 820-3209-a dead

I realized that R7022 is missing .....

Aha !! If this part is missing, then the ISL device will assume that the power enters the logic board but does not leave the other side of the current sense resistor @ R7020.

That is, the voltage may be pulled down due to an excessive load so it shuts the power rail OFF.

Can you source a 10 ohm resistor for testing ? They are dirt cheap from Mouser / Digikey, etc.

1% 0201 size. Buy spares as they are very easy to lose - trust me.

[sdogs]

Re: Macbook air 13 820-3209-a dead

Wow Top, installed R7022 recovered by another logic, reconstructed listed track and wonder seems to work, now the text for good.
thanks guys you are the light ;-)