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A2115 / 2020 / Processors from 3.1 GHz 6-core i5, up to 3.8 GHz 8-core i7. Released August 4, 2020.

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not booting black screen and no chimes

A customer of mine failed to update to Sonoma (or so it seems). Now the Mac does not boot.

I have removed the screen and have access to the status lights. The first LED on its own lights up, followed by 2 and 3 (1st 2 of the bank of 4). they then go off in reverse order and repeat.

This is without touching the power button and indeed even after I disconnected the button.

Any ideas as to where to start would be appreciated.

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There is no requirement to upgrade the OS. You can run the system on the older OS, Apple won’t remotely kill the system if you didn’t upgrade.

Now with that said, I always recommend upgrading as best as you can. You may find older Apps won’t work properly or Apple may no longer offer OS support for your system which might stop you from moving forward.

So let’s see if we can diagnose the system… As you are getting the onboard diagnostic LEDs responding we can deduce the issue is deeper in the logic. At this point I would do a careful inspection of the logic board looking for damaged components and if you have a infrared camera see if you have an area getting a bit too hot that shouldn’t be. You likely will need to take the logic board out to inspect the back side as well.

You’ll likely need the schematics and board views for the logic board so you can run deeper testing checking for shorts and checking the power rails.

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7 Comments:

Thanks for answering Dan, I will do as you suggest today. Hopefully, I will find something.

Because the problem arose during an upgrade I assumed it was some kind of software corruption causing continual reboot.

After trying all the usual recovery options, it does seem that power is going to the USB ports, but I don't think the system detects anything connected. I don't think it is a matter of the key combinations not working, more the keyboard is just not detected.

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@steveg98457 - You might have corrupted firmware if they where in the middle of doing an OS upgrade. You might want to see if you can access DFU mode first using a second Mac.

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Hello Dan thanks for the update.

I am not the most experienced when it comes to working on Macs, but I have checked what I can and have not found any shorts.

Not sure about the firmware, or rather if it can be recovered. What seems to be happening is that it is power cycling. The first LED comes on, then the second and the fan spins up, the third LED comes on, then after maybe 10 to 15 seconds they all go off with the fan spinning down, it just repeats this continually. All this without touching the power button.

It never seems to lose the 12v supply to the logic board.

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I have tested the power button and it is functioning correctly.

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@steveg98457 - Review this How to revive or restore Mac firmware it’s not that uncommon to get into this issue during an OS upgrade when there is a bit power disruption.

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SteveG will be eternally grateful.
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