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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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Displays an Apple for about 20 seconds and then reboots. Any thoughts

This iMac was brought to me for data recovery after a lightning storm. It powers on and boots straight to an Apple, no status bar, and then sits there for about 20 seconds before silently restarting the process. The iMac A2115 27" 2020 does not respond to wired or wireless keyboard inputs for option boot, target disk mode as well as both internet and non internet recovery and diagnostics. I can zap the PRAM, once, and upon reboot the machine returns to its previous state. It will only reboot once no matter how long option -cmmnd-p-r is held down. The audio, present after the first PRAM reboot, returns to silent for further reboots until PRAM is attempted again. I was successful in getting the mac into DFU mode and was able to revive the software with zero errors, but zero effect. I have pulled RAM and tested with known good RAM and the issue remains. I am at a loss and throwing this out there to see if anyone can help. I'm just trying to get the data off. Cheers!

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The issue is a breakdown in the power circuit. As you are getting power for a short window, this should be recoverable!

You will need to trace out the power lines from the socket to the power supply and then from the PS to the logic board to see if the power is even getting to the logic board in a steady state.

You may also encounter issues within the logic board power rails, again tracing them out.

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4 Comments:

At first I too thought it was power related, but the machine will remain power on in DFU mode for hours, if not days. I even thought about something power related to something further down the POST than what DFU mode requires, but you should still be able to boot into apple's diagnostics and expect it to power down, but it won't even let me in. Thank you for the input. Cheers!

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@macisaac - DFU mode uses the Intel graphics engine not the AMD Radeon GPU, so it could be focused within the GPU power rails when they are active.

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That would prevent a low level state such as target disk mode and Apple Diagnostics?

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@macisaac - Its possible! I've not encountered you exact condition so I can't say.

The fact you got into DFU mode tells me the CPU is working, it may not be under stress of ruing the OS and other stuff so that also holds while you are winking-out as the power to it is not stable. This could be a VRM issue (the power control logic for the CPU) or anything south of it!

This needs someone to trace the power from the AC outlet on the back of the system to the logic board to see if the PS is the issue and then picking it up at the logic board tracing out the power rails.

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macisaac will be eternally grateful.
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