820-2936 green light, turns on but do not charge the battery

[Gustavo Gomes]

I have a board here 820-2936, it have signs of previous cleaning, with some junk here and there, but did not find any corrosion.

This board turn os with charged battery, works fina and stable.
Charger only stays green and it sees the charger and battery, but won't charge.
I cleaned the board properly and did some measures on the current sensing circuit, all resistors seems to be fine.

I'am suspecting of a bad SMC, I need a little help with some SMC measurements, to state if just crap under it or it its failing.

 

[dukefawks]

If it runs off the battery and see the percentage SMC is fine. Most likely cause is corroded resistors/traces in current sense circuit. Measure at the pins of U7000 between 17/18 and 27/28. Make sure all power is removed and discharged!

 

[Gustavo Gomes]

U7000 measurements in diode mode with no charger and no battery:

From pins 17/18 - 139
From pins 27/28 - 018 and beeping!

Im looking at this line but R7021 and R7022 9.8ohms both.
C7020 and C7021 no short.

Bad ISL?

 

[dukefawks]

17/18 is not correct so corroded resistor or trace in that circuit.

 

[Gustavo Gomes]

R7052 reading 89ohms, should be 0 right?
I'll replace it and test again

 

[dukefawks]

Yes that is what it says on the schematic.

 

[Gustavo Gomes]

Replaced R7052 and pins 17/18 now beeps.
removed C7050 still beep.
removed ISL still beep.

Checked on a donor board pins 17/18 should be around 1000?

 

[dukefawks]

Of course it will beep, it should read about 3 Ohm. Put back ISL and it will work.

 

[Gustavo Gomes]

Ok, that confused me, my donor board must be faulty at this region too, it's not beeping.
All this lines goes to R7020 that is just 0.02ohms, now I see, thanks for the help!
I'll post result soon.

 

[Gustavo Gomes]

ISL placed pins 17/18 beeps, pins 27/28 beeps, all resistors on this line ok, no shorted caps, still not charging.
Q7085 getting a little hot, don't know if this behavior is normal.

 

[dukefawks]

PPBUS voltage with battery disconnected?

 

[Gustavo Gomes]

Looks like its oscillating from 11v to 16v with battery disconnected and magsafe 60w(genuine)

 

[dukefawks]

That still means the ISL is not able to regulate PPBUS. Check again resistance between pin 17/18 and 27/28 at the pins of the ISL. If they are in the 3 Ohm and 20Ohm range that is ok. Could still be a bad ISL too.