iMac turns itself very completely off. Very difficult to start up.

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49 points

iMac turns itself very completely off. Very difficult to start up.

I have a brand spanking new 27" iMac replacing a mid-2010 27" iMac. Two times overnight my iMac has turned itself off and would not turn on until I unplugged the 2120 VAC cord at the back for 10 seconds, plugged it back in, and again pressed the power button. However, it did not turn on showing the normal requirement for password, it turned on showing both administrator logins. If I do a normal turn off and turn on, or a restart, it comes up with only one login.

In the preference Energy Saver, I am scheduled to turn on every morning at 7:30 AM but it is not scheduled to turn off at all.

This iMac is working differently than my old iMac from whom all settings were transferred, allegedly.

iMac 27", macOS 10.13

Posted on Feb 4, 2020 9:41 AM

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Answer 1

Top-ranking reply

Old Toad

Level 10

210,365 points

Feb 4, 2020 12:26 PM in response to Gil Woolley

That sounds like a bad power supply. Had the same problem on an earlier iMac.

First make sure you have a current and complete backup of your hard drive.

Make an appointment at the nearest Apple Genius Bar for a free diagnostic check. Tell them they can erase the hard drive for testing (this assures them that there is no 3rd party software that might be contributing to the problem).

If you want to speed up the process (I had to take the machine in twice) you can boot into the recovery volume, erase the hard drive with Disk Utility and resinstall the system without migrating any of your files over and test it that way. If it still crashes and won't boot without unplugging the power cord that essential confirms the problem. Then take it in to Apple to test and repair.

Note: If you make a clone of your boot drive on an external HD it's much quicker and easier to restore all the files as you can boot off the EHD and clone it back to your internal boot drive.

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Answer 2

Gil Woolley Author

Level 1

49 points

Feb 4, 2020 2:16 PM in response to Old Toad

Old Toad. Love the name. I have two bootable backup drives. One by Carbon Copy Cloner, one by Super Duper. Also a third drive with Time Machine. Not that I'm paranoid at all.

Working with an Apple advisor, we suspect that my ancient powered USB hub is causing the problem. Next time I want to leave the computer overnight, I will eject all my external hard drives and then disconnect the USB hub. See if the computer shuts down again. Go without any backup hard drives connected overnight.

I have also asked the manufacturer of the USB hub to tell me if there is an updated driver for the hub.

I am searching The Internet for mac compatible USB hubs. Not really getting much helpful so far but early in my search.

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Answer 3

Gil Woolley Author

Level 1

49 points

Feb 5, 2020 10:20 AM in response to Old Toad

Old Toad,

Last night, I left the computer on with all USB connections disconnected. The computer did not shut itself completely off and did not require unplugging and replugging the120 VAC cord at the back. I conclude that my USB hub is causing the problem. Either the manufacturer sends me a new driver or I have to buy a new USB hub. All three of my backup drives plug into the hub and the hub plugs into the back of the computer. The hub would seem to be able to do something unwanted to shut the computer down very thoroughly. Is there value to Apple to discover how this is happening?

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Answer 4

Gil Woolley Author

Level 1

49 points

Feb 5, 2020 7:51 PM in response to Old Toad

The hub is indeed AC powered with a wall wart. It has worked with my almost 10 year old iMac but causes problems with my new iMac. Not too surprising. The problem never occurred with the old iMac. Happened immediately with the new iMac.

In the market for a new AC powered USB hub.

As long as I remember to eject all my external hard drives and then disconnect the hub from the iMac, I don't seem to have a problem.

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