820-00840 wont install OS

[Kyle93]

Arrived with no sighns of liquid damage. When trying to boot from recovery or internet recovery a error message occurs stating Mac OS could not be installed see picture.

Tried good known SSD with same results.

Any ideas what causes this and what to try next?

 

[2informaticos]

Try to boot from USB macOS.
Also try to start in diagnostic mode.

 

[Kyle93]

boots fine from USB macOS

No issues found in diagnostic mode

 

[2informaticos]

Try to erase/format internall SSD from USB macOS.

 

[Kyle93]

It does not load from external Mac OS now. The Apple logo will appear but the progress bar remains empty. Nothing else happens

 

[2informaticos]

Try USB boot disconnecting internal SSD.

You can also try new BIOS, clean ME; do NOT clean original.

 

[Kyle93]

Do you have a known good bios to try?

 

[2informaticos]

Recently posted on the forum.

820-00840 8HV22 clean ME.rar

drive.google.com

Try it as is, just for test...

 

[Kyle93]

I have the TL866A mini programmer and the Medusa 2. I just received the Medusa 2 and not sure on how to flash the bios from the computer to the EFI chip. Medusa 2 is plugged into the macbook through port A and port B is connected to the TL866A.

When I go to the miniprogrammer software from TL866A to select IC to 25 flash detect. No device is found.

What am I doing incorrectly? This would be the first time flashing with the Medusa 2

 

[2informaticos]

You cannot use Medusa with both ports connected at same time.

Connect TL866 to port B; should see an 8MB chip, like W25Q64 (Medusa ROM).
Flash the new file on Medusa ROM, and disconnect port B.
Next, connect Medusa to J6100 through port A.
Flash the new file on the Mac ROM.
Then clean ME, if needed.
If you changed the serial number in the new file (HxD on the PC), then also fix Fsys checksum in Mac ROM.

EVERY time you read Mac ROM into Medusa ROM, verify if get same reading one time more.
Do the same when you write from Medusa ROM to Mac ROM.

 

[Kyle93]

Thank you for the detailed explanation. The new bios was loaded successfully however the same OS installation error still pops up. See pictures

 

[Kyle93]

What can I try next?

 

[2informaticos]

Install macOS on that SSD using other machine.
Then put back the SSD on this one; check what happens.

dukefawks suspects CPU, or RAM issue...