820-00840 no brain after Big Sur update

[daninazza]

Hi everyone, I am trying to troubleshoot a 820-00840 board from my dad's macbook. He told me that during Big Sur update (from 10.10), the macbook turned off and then never switched on again.

The symptoms:

• When powered on, fan spins, trackpad clicks.
• No image (checked with light on screen), no caps lock light.
• The same happens with or without battery.

What I have tried:

• Reset SMC
• Start in SMC bypass mode

What I have measured:

• No USB activity can be detected
• Charger takes 0.5 A at 20 V (goes up from 5 V).
• PP3V3_G3H =3.4 V
• ppsv3_s4=3.32V
• ppsv3_s5=3.32V
• pp5v = 5.1 V
• PPVCCCPU_S0G stays at 0.94 V

It seems that all power lines are there but the board does not boot (PPVCCCPU_S0G remains high). I would like to try clean BIOS however I don't have a programmer and so I guess I will have to find someone that can do it for me (BTW: is there a way to clean the BIOS using e.g. a Raspberry PI?)

Probably I have forgot to measure something useful, could you please help me? Thank you in advance!

 

[2informaticos]

First of all, welcome to the forum!

You are not the first who reported BIOS corruption after failed Big Sur update.
In fact, it can happen with previous versions too.
So you need new FULL BIOS now; the problem is somewhere else than ME region.
However new BIOS MUST have clean ME region.

No matters which BIOS programmer will use, you can clean ME region by software.
You also need to change serial number and fix Fsys checksum after all.

Medusa programmer has a big advantage: can do all the job onboard, no need to desolder SPI chip.
But is not economically viable for a single repair.

Try this file, as is.

820-00840 8HV22 Medusa clean ME + PRAM.rar

drive.google.com

Maybe more available on the forum, if doesn't work.

Some videos about how to clean ME region and change (correctly) serial number can be found on the forum.

 

[daninazza]

Thanks a lot for your quick answer! Before I look for someone with a Medusa programmer nearby, is there any kind of measurement that can help me exclude a faulty CPU, just in case? Thank you again

 

[2informaticos]

Don't waste time, there is no reason for CPU to fail in macOS upgrade.