820-00426 Corrupt BIOS

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

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