820-00165-A strange partial boot

[Alex Thayer]

820-00165-A with no signs of damage. Supposedly suddenly died during an SSD upgrade and subsequent software reinstallation at another shop. When the display is plugged in, the device rapidly boot loops with a chime every 2-3 seconds during which the internal display is blank with backlight, SMC bypass, reset, etc. has no effect on this behavior. When the screen is unplugged (Testing bare board, no SSD, only speaker connected) the device only chimes once and then seems to hang forever, no question mark folder on external display (but it does recognize that an input is connected when the device starts), no caps lock, boot current seems normal until it settles in at 500-600mA and remains there. A quick check of all coils shows no major shorts, I'm starting to wonder about an SMC issue? Am I correct in thinking that the flashing question mark should show on an external display with no SSD installed, or is this limited to the internal display?

 

[Alex Thayer]

PPBUS is at 8.56V, only thing getting warm is the CPU. CPUVR_PHASE1&2 have a 0.011V diode drop with red probe on ground, this feels a bit low? ~1.8V (measurement starts at 0.4V and rises) diode drop referenced to PPBUS so I don't think it's a shorted fet. Now I'm afraid I might have a good ole dead CPU book.

 

[2informaticos]

First of all, welcome to the forum!

Low resistance on CPU coils is normal.
No problem there, if you get 1.8V for VCORE.

Dead computer in upgrade process is caused usually by corrupted BIOS.
Flash known good BIOS.

 

[Alex Thayer]

Thank you, and for your fast response! Yes, CPU supply is a stable 1.8V, just seemed particularly low to me but perhaps not.

I don't have a programmer but will either order one or a pre-programmed BIOS chip if you think this is a likely root cause.

 

[2informaticos]

1.8V is perfect VCORE voltage.
You can try with BIOS chip from same donor board.
It should tun on, but dirty ME region will may not allow you to enter macOS.
Will finally need BIOS programmer, if you plan to stay in this business.

 

[Alex Thayer]

Great, I ordered a BIOS chip on eBay programmed with my serial and will let you know how this turns out. I primarily do iPhone board repair and data recovery, so I don't have all the fancy Mac programmers, and at the moment it's probably a better deal for me to pay someone else to have figured that out. Thank you for your help!

 

[2informaticos]

CH341 is the cheapest one, maybe $5, or less.
An adapter WSON-8 to DIP-8 can be found cheap also.

I'm not so sure you will get a BIOS with clean ME from eBay...

 

[Alex Thayer]

Well, I'll start with that and also order a programmer, I'm not totally sure what the ME region is to be honest, but I'll do some reading instead of taking up your time with that.

 

[2informaticos]

Once you get the programmer, you can find clean ME BIOS dumps on the forum; if still need.

 

[Alex Thayer]

Still need to reinstall macOS and test everything, but the BIOS appears to have solved the issue. Thanks!

 

[Alex Thayer]

Update: *sigh* now the SSD is not detected in internet recovery mode. I used a BIOS chip from eBay, the seller claims it is programmed with a clean ME and this device's serial. Could this be caused by an issue with the BIOS? Or do I have a secondary issue? The BIOS corruption occurred while another shop had this device, it's not entirely clear what the original issue was, but I know they were trying to replace the SSD... I have both the original and an aftermarket they ordered, neither is detected, both get warm.

 

[2informaticos]

Probably new BIOS doesn' support APFS and the SSD is APFS formated.
Take an empty SSD and do a new installation of High Sierra, or newer macOS.
This will automatically update BIOS to APFS support.

 

[Alex Thayer]

Well that was a nightmare, resolved now thanks again, here's some notes I took that might help others:

Booted a GParted live USB stick and reformatted the internal SSD, which showed up normally, as gpt and hsf+ but there was no change in recovery mode disk utility, including when use from the CLI. You need to select journaling when formatting the drive.

Installed MacOS Yosemite onto an external SSD with internet recovery and booted successfully, but the device is completely unaware of the internal SSD.

Spent 2 hours trying to update the instillation on the external SSD to numerous macOS versions, which failed because a "firmware partition was not present on the drive", complete waste of time don't do this. Error is related to the internal SSD being in a bad mood.

Created a MacOS High Sierra bootable installer with files downloaded by DosDude's patcher using the official create instillation media command. Don't try to make a newer installer from Yosemite unless you enjoy undocumented error messages related to the application path flags you must append.

Booted from the High Sierra installer, and suddenly the internal SSD shows up, properly formatted as MacOS Extended Journaled and everything, so no clue why it couldn't see it before, but now it can be re-formatted and installed to normally.

 

[2informaticos]

To update APFS format in BIOS, new installation must be done on internal SSD.

"Take an empty SSD and do a new installation of High Sierra, or newer macOS."
I didn't mention USB, supposing you understand to connect internal SSD.

 

[Alex Thayer]

That wasn't my exact issue, I tried multiple internal SSD's that had been formatted as gpt and MacOS Extended (Journaled) and they still didn't show up, unless I'm misunderstanding that shouldn't have anything to do with APFS?

I also didn't have a macOS High Sierra installer on hand, and needed to get something up and running in order to create one, which is why I needed the external USB SSD.

Just wanted to leave some tips if someone else is ever in a similar situation.

 

[2informaticos]

I hope you've understand that buying preprogrammed BIOS chip is not worth.
Get an USB programmer and flash the chip yourself; save time this way.

 

[Alex Thayer]

Yes, I also purchased a programmer at the same time, I just don't have time to dive into figuring that process out right now. Thank you for your help with this board.