820-00165 Random green light on charger

[ahoonid]

Hey everyone,

I have a MacBook Air 2017 with a weird problem. The MacBook was totally dead at first and the culprit was the C7430 capacitor which was obvious upon initial inspection as it had a fracture on its surface.

The F7140 fuse was also blown so I changed them both. L7130 due to corrosion was also replaced. Now everything works again. Laptops turns on and everything seems reliable at this point.

The only issue that I'm afraid might bite me in the ass later is the magsafe light as it randomly changes light from orange to green while charging. Other times it completely turns off while still drawing power around 45mA but of course doesn't charge anymore. In this state when I put it under load it draws the normal 2 to 3A but no light yet again.

I couldn't find a pattern since the issue happens with or without load. The IO board and cable were also replaced with no change.

I'm just hoping it's not the SMC.

Appreciating any helps in advance.
Cheers.

[mon2]

Check and/or clean the pogo pin mating contacts with a cotton swab and ipa (alcohol). Be sure the contacts are clean and shiny without any dirt or cat hair, etc.

Be sure the 3v42 rail is stable. Confirm the operation of the dual common cathode diode that powers the 3v42 regulator. It is a common failure point on this model. This rail is required to light up the MagSafe led head.

[ahoonid]

Thanks Mo2 for your suggestions and help.

The charger's pins are fine. It's connected to my power adapter and the issue is with this laptop only.

The 3v42 line seems stable. Even when the charger light is off sometimes, I still have the line with correct voltage! By the mentioned diod you mean D7005? That's not showing any abnormal behavior either.

Could this be a CMS issue at all?

[mon2]

Review this thread:

https://boards.rossmanngroup.com/thr...-to-o-s.48239/

[ahoonid]

I've already come across that thread and I believe it's not the same as my issue. I've already swapped the IO board and its cable with no change. Could there be a small short somewhere? If yes, where would you believe I should check for it?

I just find it weird how the charger is still drawing power when the magsafe light is off and the system works as expected and normal. Somewhere along the way the battery stops charging and starts charging again! But I can't figure out where.

Thanks again Mon2.

[mon2]

How old is the battery? How many charge cycles? Test with another battery. Amazon is good for quick sourcing and can be returned if not required.

[ahoonid]

I suspected the battery and have tried another one with the same behavior unfortunately.

[ahoonid]

Original battery has around 800 cycles and yeah probably not much left of its life. But the other battery whicharound 500 and doesn't show this weird behavior behavior on its own device.

[mon2]

The 500 charge cycle battery also shows the strange behavior on this box but ok on another?

[ahoonid]

Precisely.

[mon2]

Remove all power. Meter in resistance mode. Measure the resistance from pins # 17 and # 18 of U7100. Measure directly at the charger IC U7100.

[ahoonid]

Pin #17: 3 not giving me a number! Ranges from 3 kOhm to 40 kOhm and going up. Sometimes around 100.

Pin #18: Gives a number. Most of the times 107 kOhm.

[mon2]

To clarify, place one meter probe on pin # 17, other meter probe on pin # 18. We are wanting to confirm the full path resistance of this current sense loop.

[ahoonid]

Ahh ok I thought you wanted resistance to ground.

53 kOhm is what I get then. Really hard probing tho as the pins were by each other and very small 😁

[mon2]

Ok. These measurements are way off from the required resistor values. Proceed now to measure the resistance across:

R7151 ; should be ~2 ohms
R7152 ; should be ~0 ohms

One meter probe on one side of the resistor; other probe on the other side of the resistor.

With the 53k ohm resistance, the root cause is here. The charger IC is measuring the voltage that enters the battery charge rail and the voltage that leaves the same rail. From the voltage drop across the current sense resistor @ R7150, the charger IC can calculate the current draw. That is, it can determine if the load is consuming the proper amount of current.

With a massive load like 53k ohms, this is way too high and the charger IC is shutting down the charging of the target battery.

[ahoonid]

I'm getting 2 and 0 ohms as you mentioned. At this point should I go ahead and replace U7100?

[mon2]

Not yet. Review Q7180 which is often a root cause of these issues. Carefully, measure the voltage to ground of pins 1 or 2 to ground. Check pins 4 or 5 to ground. Post each measurement.

Reference:

Magsafe Sleep Mode - LogiWiki

[ahoonid]

This might be a very stupid question but the q7180 mosfet only has 4 pins as far as I see but the board view shows pin 1 to 6 under it! How does that work? 😅

I'm getting 20v throughout the mosfet with my psu connected, and 15v when connecting original 45w magsafe which are normal I suppose.

[ahoonid]

I read the reference logiwiki and compared the behavior of an original magsafe against my psu. With the original magsafe connected to the bare bone MLB, I get random turning off of the orange light and turning back on, and the fan starts to spin at high speed.

with the psu however, the charger is green then orange then green and this goes on until the light is off and shortly turning back on. Sometimes it draws power and the fans are on but most of the times it's not drawing any power when the psu is connected to bare bone MLB. When everything is connected, specially the battery, the psu draws more power and charges as explained before.

[reformatt]

Connections to Q7180 are under the MOSFET itself.

Genuine Magsafe adaptors have a load detection before turning on the full voltage. Knock off's don't do that and apply the full voltage regardless (hence you get sparks sometimes when connecting them). BTW, this detection is within the magsafe connector not the actual power brick. To check this is working right, connect only the battery, and check voltage on R7012. Anything above 0V, then battery voltage is leaking back through Q7180, or in some cases via a leaky D7005. I've also had a corroded R7180 cause similar issues as well.

SMC controls battery charging, so if a valid Magsafe isn't detected, then battery charging is disabled. Pertinent signals are SM_BC_ACOK and SYS_ONEWIRE. The circuitry for the one wire circuit is contained in the LIO board, but you can refer to the older A1278 820-3115 schematics for how it works. SM_BC_ACOK must be high in order to provide power to the IC for SYS_ONEWIRE. The one wire circuit is how the SMC determines the wattage of the adaptor so it needs to be functional for correct operation.