820-01041 Macbook Pro Not booting

[aed040]

I left my wife's laptop running and when she is going to use it it is no longer booting.

Trackpad not clicking

Top right and lower left USB-C is reading 5v and 0.15Amps on the charger
Bottom right and top left USB-C is reading 5v and 0.08Amps on the charger


I only get millivolts on PPBUS_G3H @F7000 in both pin 1 and 2 when charger is connected


Resistance measurement without charger
Ground to PPBUS_G3H 22.9Ω
PPBUS_G3H to L7211 24.9


I also check the resistance with the charger connected and the readings also changes
With charger connected on 1st port that is pulling 0.15Amps
Ground to PPBUS_G3H 25.8Ω

And with charger connected to 2nd that is pulling 0.08Amps
Ground to PPBUS_G3H 2.4MΩ


What else should I check and do next?

[mon2]

Re: 820-01041 Macbook Pro Not booting

Hi. Do not do any voltage / current injection till we know more about the board.

No liquid spill ?

PPBUS_G3H @F7000

Remove all power / remove battery.

Remove fuse F7000 off the logic board. Then check the resistance to ground again on the PCB pads of F7000.

Which side is with the low resistance? The producer side (ISL) or the consumer side (downstream) ?

If the producer side is NOT the side with the low resistance, power up again without this fuse. Measure the voltage to ground of the ISL side of the fuse PCB pads.

Post each measurement.

Be sure you are using the official or at least a known good type C power adapter.

[aed040]

Re: 820-01041 Macbook Pro Not booting

Hi. Do not do any voltage / current injection till we know more about the board.

No liquid spill ?


Remove all power / remove battery.

Remove fuse F7000 off the logic board. Then check the resistance to ground again on the PCB pads of F7000.

Which side is with the low resistance? The producer side (ISL) or the consumer side (downstream) ?

If the producer side is NOT the side with the low resistance, power up again without this fuse. Measure the voltage to ground of the ISL side of the fuse PCB pads.

Post each measurement.

Be sure you are using the official or at least a known good type C power adapter.

No liquid spill

After removing F7000 and F7001 Pin 2 of F7000 has the lower resistance 22.9Ω
Pin 2 is the ISL side right?

Edit: After checking the schematics PIN 1 is connected to ISL so I checked the voltage and I am getting 12.29v now.

[aed040]

Re: 820-01041 Macbook Pro Not booting

Hi. Do not do any voltage / current injection till we know more about the board.

How can I check if it is now safe to inject voltage?

[mon2]

Re: 820-01041 Macbook Pro Not booting

Do you have an adjustable power supply ?

If yes, you can dial it up to 0v8 and then apply it to the side with the low resistance to ground.

When you do this, the voltage must be kept low, just in case the same voltage rail is leaking to the CPU rail.

As you apply this voltage, the 'shorted' component will heat up. Ideally it should be a bad capacitor but could be the CPU. If it is the CPU, then the fault is very serious.

The caps used by Apple / Foxconn are often tantalum caps which just short circuit over time and raise issues like this one.

When you apply this external injected voltage, you are NOT powering the logic board - it is only using the external DC power supply at a voltage under 1V - always. Then check who is heating up on the board.

You can pour IPA (alcohol) and see where it mists away from the heat.

Post your observations.

[aed040]

Re: 820-01041 Macbook Pro Not booting

I tried injecting voltage 0.8v and it is only pulling 0.06amps. Nothing is heating up

[aed040]

Re: 820-01041 Macbook Pro Not booting

Against all the warnings on this forum I went ahead and increased my voltage to 2v and found that U6960 is heating up.


What causes this to fail? The last thing I did was I used a powerbank with a USB-C PD port to charge it. I did not charge it longer than 10 seconds. I was just testing the powerbank if it can charge it. I saw the thunderbolt icon on the battery and then I removed the USB cable. It was running the whole day when I left it on the table and then it wont boot anymore the next day. Can a faulty USB-C PD charger do that damage?


Do you have any tips when replacing this part? I do have all the tools its just that my soldering skill is probably not enough as this is just a hobby for me. It will be my first IC of this size. northridgefix and ross make it all look easy.

[mon2]

Re: 820-01041 Macbook Pro Not booting

See attached.

It is possible that a cap that is nearby is heating up rather than the IC @ U6960.

Unless known for sure, apply flux and carefully remove C6900 and C6961.

Then measure the resistance to ground of the pads for this input rail.

Is the resistance higher than before?

Hoping that you have a shorted cap and not U6960 itself. However, the repair should not be too difficult but suggest to practice the process on some donor / dead boards available from Aliexpress.

The trick is lots of flux, enough heat and enough air pressure to melt the balls under the IC. Spin the hot air tool in circles to melt the original solder. Do not allow for the surrounding parts to go flying.

With tweezers, gently nudge the corners to see if the solder is melted.

Then remove the IC when it is. Allow for cooling -> use IPA to clean the flux -> apply low temp leaded solder by skimming the top surface -> use point to point soldering iron and nice braided solder remover to flatten the BGA pads. Do not rush else the bga pads will be ripped off the PCB and then it is game over.

IPA to clean up again.

Flux again and apply the fresh replacement IC. Take pics of the original IC so you know which side is pin # 1 !!!

If in doubt, post back or even consider to ask a local who has cell phone experience. If someone local can replace the iphone TRISTAR ICs, they can handle this replacement.

[aed040]

Re: 820-01041 Macbook Pro Not booting

I used an infrared camera and U6960 is the only one glowing.

Is it still possible that the caps are shorted? I would love it to be the caps.

[mon2]

Re: 820-01041 Macbook Pro Not booting

I used an infrared camera and U6960 is the only one glowing.

You can try the removal of the 2 caps but it sounds like the IC @ U6960 is shorted and will need to be replaced.

Before doing so, what is the resistance to ground at the OUTPUT of U6960? Is it shorted or with a very low resistance ?

Fairly sure the IC is the root cause but worth a quick check anyways.

My suggestion is to call around for a local experienced shop for cell phone repairs at the component level. From my past travels to Manila, you have good tech guys around - many semiconductor companies in the area as well so you should be able to locate a local geek to do the work in a heartbeat.

[aed040]

Re: 820-01041 Macbook Pro Not booting

I finally replaced U6960 and the short is gone. Good thing I bought 3 pieces of the IC because I failed on my first try and on the 2nd it did move to its correct place while heating it up. Hopefully I soldered it properly.


I also ripped the pads on C6900 because I accidentally pulled the wire that I soldered on the pad when I injected voltage. I already replaced the pads and waiting for it to cure before I solder back the caps.


Anything I should double check before I plug the charger?

[mon2]

Re: 820-01041 Macbook Pro Not booting

On the soldering of U6960, apply enough flux and hot air in top side circles to melt the underside balls of the component. The BGA will naturally sink into place when it is in the liquid state for the solder balls.

Allow it to cool and confirm the short is gone.

As always the resistance / diode mode checks are without any power to the logic board.

The cap @ C6900 is only 2.2uf and will not be missed. If you have removed each of the front side caps for the input to this BGA, then do place some / all of them back. Check the resistance to ground of this input again after the processing.

Confirm the resistance to ground of the output as well @ L6960 and L6961.

[aed040]

Re: 820-01041 Macbook Pro Not booting

resistance of PPBUS_G3H to ground is not static and it changes from 1MΩ to KΩ

C6900 resistance to ground is same as PPBUS_G3H and looking at the schematics it looks like they are indeed connected.

L6960 & L6961 resistance to ground is 6Ω that is also PP3v3_G3H_RTC_X so is this shorted?

[aed040]

Re: 820-01041 Macbook Pro Not booting

I plugged the charger and its now pulling 2A @ 5v
If I plug it on the other USB port it is just using 0.8Amps

The voltage at PPBUS_G3H is cycling it goes up to 12.3v and then it goes down and then back to 12v again.

Cannot find anything hot on the board using a thermal camera except the CD3215 chips which is not really hot just warm.

[mon2]

Re: 820-01041 Macbook Pro Not booting

Remove all power. Meter in resistance mode.

What is the resistance to ground of PPBUS_G3H ?

[aed040]

Re: 820-01041 Macbook Pro Not booting

its not static and it ranges from 4MΩ and then it slowly goes down to 1-2KΩ and then when I test again after a while it is high again and then slowly goes down again