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Modèle A1419 / EMC 3070 / mi-2017 / Processur Kaby Lake 3.4, 3.5 ou 3.8 GHz Core i5 ou 4.2 GHz Core i7 / Écran Retina 5K

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iMac powering off AND on randomly

40 days ago my 2017 27” iMac started powering off and on randomly. It would stay on for anywhere from 10 seconds to a few minutes, shut down again, and also randomly power up again. As on old ACSP, I did all the tricks I can think of and then brought it to Apple, who couldn’t replicate the issue of course. So I brought it home again and it worked fine for 40 days, but now it’s doing it again.

What I find interestIng is that often right before it shuts down, I see the shut down dialog (are you sure you want to shut down…) appear. It’s also interesting that it powers on again after a few seconds or minutes. Haven’t yet found another case that mentions these things. Anyone have reason to believe it’s anything other than a bad power supply? BTW also keep this iMac on a UPS with AVR. Any advice is appreciated.

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You should not be getting the shut down dialogue with a failing PSU. This leads me to believe that it's a software issue. I've seen this with systems installed on unsupported Macs. What system are you running?

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Thanks for the response! I’m using Ventura with all current updates, which is indeed supported. The startup thing is confounding too. Have you seen this before? Can’t think of any reason it would start up on its own accord. Could the power button itself be the culprit?

par

Do you get any message when it restarts?

par

Just that “your system has restarted due to an issue” or something to that effect, asking if I want to reopen windows.

par

Seems you were correct about it being a software issue, as a clean OS install seems to have done the trick. Thanks!

par

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I’m suspecting you have a outlet power issue. Get an outlet tester see what it tells you.

I think you have a bad ground or the hot & neutral wires are reversed.

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Outlet tester tests fine. Also using UPS with AVR. Happens with or without the UPS. Relatively new home with pretty clean power.

par

@nuages - What does the console tell you? Look at the log file. You might want to flush it as it can get quite big!

I don’t think you’ll see anything as the output at the time-point won’t be saved.

Let’s follow the AC path from the UPS to your system are you using the protected outlet and directly connected? Try replacing the power cord and do a good inspection of the systems socket for arc damage and/or dirt. You may need a new socket.

par

I’m up in the hills, so I’ll have to check console again when I get home in a couple of days. I’ll probably wipe it and do a fresh install as well for testing purposes.

The iMac plugs into the cyberpower CP1000AVRLCD, battery/AVR side. The UPS plugs right into the wall. I’ll inspect the outlet when I get home. I’ll try a new power cord for the iMac as well. Thanks!

par

Back home. To be thorough, I plugged directly into another outlet, which I had checked for wiring faults, used a different kb/mouse, and a different power cord, no peripherals. Same thing happened.

So I went nuclear and reformatted the internal drive & clean installed Ventura -- probably overdue, as this Mac has been upgraded every year since 2017. I'll rebuild manually rather than migrate the data and see how it goes, but so far so good. Maybe it's fixed or perhaps playing coy before it acts up again, but this way I'll know eventually.

Regardless, thanks for your help in troubleshooting!

par

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Nuages sera éternellement reconnaissant.
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