A1502 820-4924 Question mark folder

[donnos]

A1502 820-4924 does not boot into anything except ? folder. No diagnostic, no recovery, no external, not even startup manager. Customer said he erase the macbook from icloud and now we can't reinstall macOS anymore. Just so coincidence this is a hardware fault?

tested on another chasis to rule out KB and TP issue.

 

[VinceLx]

Without internal SSD, did you try to boot on a old OS X (e.g 10.13) in a USB key?
I had cases where internal SSD prevented to recognize other boot possibilities

 

[donnos]

yeah, i tried without the internal SSD but with external HDD with various macOS installation in it plugged in and none booted

 

[Mac Tech]

try another clean bios

 

[2informaticos]

Did PRAM reset?

Faulty TP/KB communication will not allow you to enter boot menu.
Connect preinstalled internal SSD.

 

[donnos]

have tried Clean Bios, no difference.
i did use a known good chassis to rule out kb/tp issues but still same. and i know keyboard is ok because capslock lights up when i press it

Yes tried preinstalled SSD also it still boot to question mark folder.

PRAM reset seems like it does nothing. from DCPS reading, it looks like when i press on the button combo it only stay black screen (i held it a good 5 mins just to be sure), it hovers at about 700ma until i release, it drops to about 450ma and the folder logo appears.

 

[2informaticos]

Using known good keyboard doesn't discard a problem with KB circuitry on the logic board.
If you can't access boot menu, must be a problem in that area; U4820/30, especially U4850.
But this shouldn't cause SSD issue.

BIOS file without APFS support can cause this, if you try to boot APFS macOS.
However, will not explain missing boot menu option.
Where did you get the BIOS file?

 

[donnos]

the Bios file is from my test bench unit(which runs fine), exact same model/specs/year. i dump it, clean ME and flashed.

i measured U4820/30/50 and all 3 are within good readings. not planning to swap just yet

 

[2informaticos]

"my test bench unit(which runs fine)"
Does it run APFS macOS?

TP circuitry (on MLB) can also cause the KB/TP not working before macOS is loaded.
KB/TP may need to work in USB mode (before macOS loads SPI driver), in order to acces boot menu, or do PRAM reset.
Can do PRAM reset?

Also EFI password can be an issue.

 

[donnos]

Yes it runs on APFS, so update. i checked the EFI and i forgot that i had password on, so i cleared it.
now i get apple logo and boots! great! i get into OS and tested KB and TP, all was fine.

BUT i'm still not able to get into diagnostics, recovery or startup manager. could my bios be somehow f**ked?

 

[2informaticos]

"KB/TP may need to work in USB mode (before macOS loads SPI driver)"
Remove SSD and check TPAD_VBUS_EN; TPAD_SPI_BUS_EN must stay low at same time.

 

[donnos]

so this is now resolved.
i did a full reinstall of macOS and upgrade to catalina, now everything works properly. still unsure whats the root cause.