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Late 2019, there were a series of reports that the then-latest Catalina update corrupted Mac firmware and caused computers to be bricked. My computer (MacBookPro11,1) appeared to be one of those affected. The reason why I believe this is real is because I always do a hardware diagnostic check before and after an upgrade. Before the update, the computer reported no problems. Afterwards, it reported memory problems. The hardware could've failed at that exact time, but it's quite a coincidence.

My Mac is now a door stop, but so many months later, I wonder whether there are any solutions found other than replacing the mainboard? There was also an account of someone reflashing the firmware with some tool, but there were never any details on this and I was not able to find this tool.

Anyone have first-hand experience with this that can comment?

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I can't speak with any expertise, but I can speak from experience, as two of my machines fell victim to this.

I don't know if I would call it a "corruption" issue, though it isn't too far from reality (Technically, the firmware isn't corrupt, it just doesn't boot the system. Since you were able to run diagnostics after the Mac was "bricked" I'm convinced that this was true in your case as well. Big difference, I know, the end result is the machine doesn't post, but it did make troubleshooting a lot harder for me.)

So as you said, the Catalina update involves changes to the firmware. Specifically, it updates it. Many macOS updates have included firmware upgrades as part of the process however, so why are there issues in the Catalina update?

I don't know. I can only guess. I don't think there is a way to start multiple processors in EFI, and if a big application fails, more often than not the processor resets. And it's meant to start up again, make another attempt.

But sometimes it just fails to do this. In my case, perhaps it was because I had added drivers, applications etc. to my EFI, and the MultiUpdater(?) choked on the significantly altered region of the firmware that outlines descriptors of regions and their offsets.

Since you're working on a portable, power failure seems less likely, but it's still possible, when you're making changes to the SMC, EFI, and depending on each individual circumstance, even a microcode update (sort of like firmware for the CPU, bad analogy but whatever :P)

What usually ends up happening, from my experience, and from the anecdotes I've heard, is that for one reason or another, the BootROM flash doesn't happen, and usually the update application with a bunch of drivers is left on the ROM. For me, it went into a sort of half booted state, where the bootrom has started, doesn't flash the update and is just doing nothing, and also there is nothing you can do to change its startup behavior.

For T2 Macs, there is a supported solution, you can put them into DFU mode and restore the T2 firmware (which now envelops the smc).

For non T2/T1 Macs, the solution is simpler in one sense but infinitely more convoluted in another. Basically you open up the machine, and physically access the SPI bootrom SOIC8 nor memory chip to program it using known good firmware edited to include your serial number.

That's what I did to my non-T2 iMac, which I had modified to use without an internal display installed. Getting the materials/resources gathered up takes some effort and a lot of time, but the actual flash, is done in a flash :)

Depending on where you live, there may be non-apple authorized repair shops providing this service for a lot less than what a replacement logic board costs.

I don't think I can help with the firmware, I'm pretty sure my mbp is 10,something, but you can find SPI ROM dumps, all cleaned (like an SMC reset, but more like SMC wipe and reprogram from official Intel releases) and ready for a serial number if you google around. You might end up paying around 5 bucks for it.

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  • Thanks. Do you know where I can find detailed instructions on how to reflash SOIC8 chip? – pruspila Jun 30 at 6:35
  • Hmm, not quite sure how I should answer that, not all chips have the same specs (SOIC8 is more a package size than anything else) but definitely check out flashrom, its a general tool that can, flash rom chips (at least the most commonly used ones). I used a really old Raspberry Pi 2B with a Pomona clip as the programmer. – kumowoon1025 Jul 1 at 4:36
  • @pruspila Oh, I forgot to mention, I am positive that your system model has a logic board with a populated debug connector to make things even simpler. Though they are a bit more pricey, you can do away with the Pomona clip (which can be hard to work with in cramped designs like the MacBooks have) and use a Hirosa or Molex breakout to gain access in a much more reliable way. – kumowoon1025 Jul 1 at 17:43
  • @pruspila I have no affiliation, and have never ordered from them or used their products before, but CMIZapper is a well known vendor for their specialized Mac board-level component and firmware toolkits. – kumowoon1025 Jul 1 at 18:05
  • I mention them in case flashing your MBP logic board with a $20 external programmer makes you hesitate (it was daunting for me when I first did it on a working machine). They have something called the MattCard which you can just plug in to temporarily override the onboard rom with an external chip on the MattCard programmed with known, good firmware, so you can confirm if the rom is the issue before pursuing the issue any further. Only thing is it's a tad expensive, at around $80. But you can reuse it if you ever get the same problem – kumowoon1025 Jul 1 at 18:05

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