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820-00426 Corrupt BIOS

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rvanpruissen

Member
Got this one braindead; running fans, but nothing else. Reflashed BIOS with a clean one found on this forum (serial changed + checksum fixed) on a different chip and it came to life. Started a Big Sur install, crashed while loading the installer and now it's looping; fans spin for a while and it seems to reset, no backlight.

I think it's got itself corrupted again. Likely bad CPU/PCH?
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UPDATE: Hmm, it now seems to work somewhat again. Will try another battery to rule out problems with that.
 
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2informaticos

2informaticos

Administrator
Staff member
Test it with known good working battery.
Be aware, many people complain about BIOS corruption caused by Big Sur upgrade.
 
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rvanpruissen

Member
Checked with new (iFixit) battery, still trouble. Gets stuck loading the MacOS installers a few tries and then only bootloops (turns on, fan spin, no image/bl turns off).

Guessing CPU/GPU. Any other suggestions?
 
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rvanpruissen

Member
I think I'm at the same point now. With 'working somewhat' I meant it was showing question mark folder. After Adding a bootable drive, I never got to an OS.
 
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rvanpruissen

Member
After a safe boot from an external MacOS installation, the laptop started behaving again. Installed Big Sur to update the BIOS for APFS support.

Never tried this approach. I thought safe boot only disables 3rd party stuff. Does it also try to fix things?
 
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rvanpruissen

Member
Ok, so this just failed again. Customer successfully used it to do a full backup a while ago, left it for a while (±a week) and today it worked for 5 minutes and died on him again. Anything still to try on this one or should I give up?
 
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