Macbook Pro A1708 blown cap...

[TheMoebius]

Hi guys!

Got a Macbook Pro A1708, I had it open as I was replacing the display, I foolishly didn't disconnect the battery (I know), next thing the trademark smell of a blown cap. Grim.

I think one of the cables for the new display has touched something briefly on the main board and shorted something.

I disconnected the battery as quick as I could, but something has blown. Can't see any damage to any of the chips on either side of the main board.

Where do I start with this? All I have is a multimeter.

Any help appreciated!

[mon2]

Re: Macbook Pro A1708 blown cap...

The defect could be anywhere on the logic board.

1) Any fan spin when you turn ON the laptop ?

2) Does the CAPS key on the keyboard toggle the LED on / off with a keypress ?

3) Do you have the schematics and boardview file for your logic board ? What are the 820-xxxx markings on your logic board ? The A1708 shows 2 different logic boards (820-00840 and 820-00875). This part number will be etched on the circuit board.

4) Is the power adapter still working ? It is the USB Type C style so perhaps you can test it with another widget in your shop ?

[TheMoebius]

Re: Macbook Pro A1708 blown cap...

Thanks for the reply!

1) The fan doesn't spin, keyboard doesn't light up or anything - its totally dead.

2) No caps lock, totally dead.

3) 820-00840-A I don't have any schematics for it though.

4) The PSU definitely works OK.

[mon2]

Re: Macbook Pro A1708 blown cap...

Download the schematic from here:

https://www.badcaps.net/forum/showth...0840+schematic

See attached -> measure the voltage on both sides of fuse @ F7000.

This is a critical power rail for the logic board = PPBUS_G3H.

Meter in 20V DC scale.

Red meter probe on F7000 (pick either side) + Black meter lead to ground.

Then check the other side of the fuse with the red meter probe.

This should be with the external AC power adapter (Apple original).

Post your measurement.

[TheMoebius]

Re: Macbook Pro A1708 blown cap...

Thank you so much.

Will port results shortly!

[TheMoebius]

Re: Macbook Pro A1708 blown cap...

Unfortunately it's not the fuse. Getting 12v either side of it.

[mon2]

Re: Macbook Pro A1708 blown cap...

What is the exact voltage of PPBUS_G3H ?

[TheMoebius]

Re: Macbook Pro A1708 blown cap...

Looks like 12 volts either side. I will check again with a better multimeter tomorrow. Is there anything else I can look at in meantime?

[mon2]

Re: Macbook Pro A1708 blown cap...

On such logic board designs, the decimal place accuracy of the voltage reading is important.

See here about PPBUS_G3H:

https://logi.wiki/index.php/PPBus_G3H

So is it 12v2 or is it 12v6 ?

The 12v6 kicks in once the SMC controller has requested the regulator to boost the voltage rail. The exact voltage on this rail will help to decipher how much of the logic board is working.

Also, you must be very careful in working with the logic board in general if the battery is connected. Review on youtube on 'A1708 battery replacement' and it will show how to disable the current battery from the logic board.

Otherwise, you are 'live' voltage on the logic board unless the battery is known to be completely discharged.

Once the voltage is removed off the logic board, you can perform resistance checks to ground for the large grey coils = switching power supply inductors. If indeed a cap is blown, it may be visible to the eye(?), the resistance to ground for that rail will be very low.

Is your multimeter a digital or analog unit ? This work will require a digital meter although I grew up with a Tandy (aka Radio Shack) analog multimeter - learned so much with that tool. It was my equivalent of a stuffed teddy bear. RIP analog meter. Ok, wiping away my tear now.

[TheMoebius]

Re: Macbook Pro A1708 blown cap...

Aah thanks for the info, didn't realise it was that important, I thought we were just checking if the fuse had blown haha. Yes it's an old analog meter as I couldn't put my hands on my digital one, but will make sure I get it tomorrow.

Thanks again for your help, its really appreciated!