820-00165 Not booting after Big Sur upgrade

Kappy

Member
I've got a 2017 MBA which the customer brought in after installing Big Sur (I think they did an upgrade). They reported that after the install completed the MacBook wouldn't boot at all.

If I try and start the MacBook the fan will spin for about 4 seconds then stop and restart again. I've check the board and there's no liquid at all very clean. I also checked the power rails and they are all present all the way to CPUVCORE.

I've tried to clean the ME (i'm not sure if it was done properly) and it's still the same. I've also tried about 6-10 different dumps that I have which I know have worked in the past and even tried one that I found on here '2017 - J1WK clean ME - working - 1.8Ghz_8GB' all of them are doing the same thing fan spin stop and then start again.

Not sure what else to try and would really like some help.

Thanks in advance.
 

2informaticos

Administrator
Staff member
BIOS corruption can happen after some macOS upgrade.
But if you already tried several dumps without success, there must be something else.
Probably the client doesn't say all the true.

Try the dump from the forum as is, don't change SSN.
 

Kappy

Member
If I upload the original do you think it's worth cleaning the ME, would that make any difference?

I don't have a Medusa so i'm using some software that I found whilst a long search...
 

Kappy

Member
Just tried the customers SSD in a spare 2017 MBA I have and indeed they are telling the truth as it completed the upgrade of big sur on the SSD..
 

Kappy

Member
This is very strange as now I must have tried over 20 different types of BIOS and all of the do the same thing. Fan spins for about 4 seconds, stops and then starts again but no chime or screen activity both int and ext. Tried SMC reset still the same. CPUVCORE is 1.7v

Is there anything else I can check?

Do you think the BIOS chip has been damaged even though i'm able to program it without any errors?
 

2informaticos

Administrator
Staff member
Ooops, PCH misses some previous signal, or has an internal problem.
Check CPU_VCCST_PWRGD and CPU_VR_READY.
Be sure pin 3/U1950 is high.
 

2informaticos

Administrator
Staff member
Heat PCH area with quality flux.
You can heat entire CPU, just in case.
No more than 180-200 degress, for 15-20s; no need to melt the balls.
 
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