Q: imac shuts down in sleep mode

Power or other problems related to unexpected system sleep, shutdown, lights or fans justify an SMC reset. Read all the steps.

Before Resetting the SMC

Try each of the following steps in this order before you reset the SMC. Test the issue after completing each troubleshooting step to determine if the issue still occurs.

1. Press Command + Option + Escape to force quit any application that is not responding.
2. Put your Mac to sleep by choosing the Apple () menu from the upper-left menu bar and then choosing Sleep. Wake the computer after it has gone to sleep.
3. Restart your Mac by choosing the Apple () menu from the upper-left menu bar and then choosing Restart.
4. Shut down your Mac by choosing the Apple () menu from the upper-left menu bar and then choosing Shut Down.

Resetting the SMC for Mac Pro, Intel-based iMac, Intel-based Mac mini, or Intel-based Xserve

1. Shut down the computer.
2. Unplug the computer's power cord.
3. Wait fifteen seconds.
4. Attach the computer's power cord.
5. Wait five seconds, then press the power button to turn on the computer.

After completing the above please determine if the problems also occur in "Safe Mode":

• Safe Mode or "Safe Boot" is a troubleshooting mode that bypasses all third party system extensions and loads only required system components. Read about it: Starting up in Safe Mode
• You must disable FileVault before you can start your Mac in Safe Mode.
• Starting your Mac in Safe Mode will take longer than usual, graphics will not render smoothly, audio is disabled on some Macs, and some programs (iTunes for example) may not work at all.
• Merely starting your Mac in Safe Mode is not intended to resolve the problem, it's to observe its performance without certain additional components.
• To end Safe Mode restart your Mac normally. Shutdown will take longer as well.

I had the same problem and tried all of John Galt's procedures on my new 2013 iMac, but they made no difference.

I found that if I disconnected my USB hub, the problem went away.  The USB hub caused a crash and restart when the computer was put to sleep even if there were no devices attached to it.  I think this entry in the Console log describes the problem:

12/27/2013 7:17:03.539 AM powerd[16]: com.apple.message.domain: com.apple.sleep.failure

com.apple.message.signature: Platform Failure

com.apple.message.summarize: YES

Sender_Mach_UUID: 5255D529-353E-3C81-A31C-8B5064DBA765

The hub was a BalanceFrom 7 Port USB 3.0 Hub with 3A Power Adapter.  I see now on Amazon.com reviews that two other iMac owners had the same problem with this hub.  I was very relieved that the new computer was not the problem.

I know this is an old topic but thank you! I have been all over the forums trying to figure out why my Late 2012 iMac is doing this. Was very worried, but it was my external hub. I don't know why it does this.

Anyways thank you for your post!

Hi everyone I have an Imac 20 inch early 2009 model that when goes to sleep for maybe 10 minutes shut down.
Let say that when i tap any key the computer goes to a dark blue to a grey then a message come up that say "Your computer was shut down  press any key to restart the computer re start okay but this happen several times a day.

Is this a power supply falling ? if I change power supply most likely ve fix or can be something else?

Thanks

Hernan

You might want to consider starting a new discussion. Since this one is a couple of years old, less people are likely to look at it. A new post would be much more visible. You can link to this one.