A1398 powering off mid boot

[Bob_1972]

Hi, Can I get some advice please. I have a 2013 15” MBP A1398 that powers off during boot and also just prior to the recovery console loading. If I boot into TGM it works fine. If I connect it to a bench power supply with an 85W Apple Magsafe 2 connector with everything connected to the logic board I get 1.75a. I hear the start up chime and the fan spins. Filevault was enabled so we get the logon screen, enter the PW to unlock the partition and part way through the progress indicator the Mac powers off and the power supply shows zero amps. If I disconnect and re connect the magsafe I get zero amps. It will then randomly power on and get to 1.75a again. If I try and boot into Internet recovery I connect ok to WiFi and the indicator counts down, when it loads the white screen with the Apple logo and about to show the macOS recovery it powers off and again the power supply shows zero amps

I never see a light on the charger and I have tried more than one charger.

All of this is persistent.

So far this is what I have done.

I have backed up via TGM.
SMC and NVRAM Reset.
I have disconnected the keyboard and the results are the same.
I have disconnected the trackpad and the results are the same.
I have removed the storage device and the results are the same, obviously just macOS recovery.
I have disconnected the IO board and the results are the same.
I have disconnected the battery and the results are the same.
I have kept the charger disconnected and tried to get into recovery with just the battery connected and the results are the same.

I have taken the Logic board and I/O board out and examined them under a microscope. There are no signs of liquid damage, no corrosion and the logic board is amazingly clean. I see no evidence that it has ever been dismantled until now. Some of the probe points are a bit discoloured but if I lightly scrape them the discolouration clears. There is a solder ball on C9822

If I place the logic board with just a single fan on the bench I can not create any issues. Same amperage and fan spin every time. Looking at Louis’ WIKI for this model I can not really see any troubleshooting steps that match my issue.

Any suggestions would be well received. Thanks.

 

[2informaticos]

First of all, welcome to the forum!

Start posting exact 820-xxxx board code.
If has Discrete GPU, this could be a good reason of the failure.
The FDMF6808N chips are also suspects, as common failure.

Try installing Windows,
Then check if crashes when you install graphics driver.

 

[Bob_1972]

Hi, Thanks for coming back to me and thank you for welcoming me to the forums I'm pleased to be here. So its a Mid 2012 2.3Ghz 8Gb which means the Logic board is 820-3332-A . Would an issue with the FDMF6808N manifest itself the way I described ? I connected a Windows 10 Boot disk and held down option to boot from it, the Mac powers off.

Thanks

Bob

 

[2informaticos]

No FDMF6808N chips there.
I mentioned that because you've said to have 2015 machine!

Now resolder U8900 with leaded solder.

 

[Bob_1972]

Hi, I have ordered some U8900 chips, they will take a few weeks to arrive unfortunately however as a punt I took "Now resolder U8900 with leaded solder." literally and resoldered U8900, the same chip, with leaded solder however it does the same. I am sure you meant resolder a new U8900?

 

[2informaticos]

Not new, resoldering original should be good enough.

However, there is an easy way to disable GPU by hardware mod; already posted on the forum.

 

[Bob_1972]

Can you give me some more guidance please ? I have no display at all now. I get the startup chimes and fan spin. So far after not being able to resolve this by resoldering U8900 I have replaced the chip for a new one. I also noticed that R9018 looked like it was coming off the Logic board, if I pushed it gentle with my tweezers it detached so I soldered a new one. I get 5v on pin 2 and 3 of U9000 but nothing at all on L9000 and pins 28-30 of J9000. I am going to replace U9000 but I am wondering what I should be seeing on Pin 1 of U9000? any ideas would be great please. Thank you.

 

[2informaticos]

LCD_PWR_EN should come high at least in the frist few seconds, when machine chimes.
If LCD_HPD goes high at same time, PCH detects LCD and should maintain L9000 voltage; LCD assembly MUST be connected, of course.