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Sometimes Mac break

Yeaterday I booted old Catalina DP on MY NMP, it showed update – DP beta 11.
I thought, ok, lets see.

Update got downloaded… reboot…. firmware update… reboot… mac is dead.

Mac doesn’t boot anymore.
It just starts up, no bootchime (and I have it disabled anyway), after like 5 mins it lights up connected display, displaying black screen on it (even tho at proper resolution)

That’s it, no boot, wait many hours, nothing changes.

PRAM reset – didn’t help. SMC reset – didn’t help..

A secret way to do pram reset – didn’t help. (take out cmos battery, it clears RTC, mac will boot in “EFI_BOOT_WITH_DEFAULT_PARAMETERS” mode next time, ignoring NVRAM on startup, at least in PEI mode)

Cool update I thought. At least I can swap ssd to macmini and get my data back.

The final solution was to get access to eeprom, it’s on bottom pcb, inside NMP.

Using CH341A/AsProgrammer (thanks Alex for CH341A), I was able to read and write the EEPROM chip with main bios rom.

I tried to make pram reset in hard way, wiping out content of two VSS partitions inside efi ( they hold nvram arguments).
That helped, mac booted.

Appearently it’s a bug in new fw of parsing some nvram params.

Apple, Wanna that firmware ? I still have that dump.

P.S. this is how mac looked for few days, still can boot it this way. bios rom IC is on the other side of pcb you can see.

nmp

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