iMac turning on as soon as power is connected

[user1234]

Since a few weeks ago, my parents are having an issue with their iMac 21". It's an Intel iMac, 2019 model. Running the latest Ventura update.

When they plug in the power after it has been unplugged it turns on. Every single time.

I have made sure start-up after power failure is turned off, as well as wake for network access. I have reset NVRAM and tried resetting SMC but the instructions are to unplug for 15 seconds, plug back in and turn it on after 5 seconds, but by the 5 seconds it's already starting itself.

I have also made sure there are no schedule for power events.

I can't find a single reason it would start by itself. I'm thinking either a software bug or a hardware problem.

Has anyone else here had this happen? Was it solved and if so what caused it?

 

[Rich B22]

Since a few weeks ago, my parents are having an issue with their iMac 21". It's an Intel iMac, 2019 model. Running the latest Ventura update.

When they plug in the power after it has been unplugged it turns on. Every single time.

I have made sure start-up after power failure is turned off, as well as wake for network access. I have reset NVRAM and tried resetting SMC but the instructions are to unplug for 15 seconds, plug back in and turn it on after 5 seconds, but by the 5 seconds it's already starting itself.

I have also made sure there are no schedule for power events.

I can't find a single reason it would start by itself. I'm thinking either a software bug or a hardware problem.

Has anyone else here had this happen? Was it solved and if so what caused it?

I'm having the same issue with my 2017 27" iMac for a few months. Since it's almost always on, I really haven't spent the time to investigate. I also don't know what has changed, but would be curious as to what anyone finds

 

[user1234]

I'm having the same issue with my 2017 27" iMac for a few months. Since it's almost always on, I really haven't spent the time to investigate. I also don't know what has changed, but would be curious as to what anyone finds

Interesting. Maybe I should test with my 27" 2017. It's running 24/7 so I haven't noticed anything but I should really try and see when I get a good window to shut it down.

 

[TwoH]

I have had this issue before on a machine - the CMOS battery was dead on the logicboard. So you're looking at a hardware problem. Fixable, if you can take the machine apart to replace it.

 

[Fishrrman]

My guess is a failure of the power-on button. It's "stuck in the on position".
Don't bother taking it apart.

Use this "Fishrrman dumb as they come™" solution:
- Buy a cheap power strip with several outlets on it
- Plug the iMac into the power strip (perhaps some peripherals, too)
- When your parents are done using the iMac, choose "shut down" from the menu as they usually would
- Wait for the shutdown, and "the spontaneous reboot" sound.
- At that point, IMMEDIATELY REACH DOWN AND TURN OFF THE POWER STRIP.

When they're ready to boot the iMac again, just reach down and TURN ON the power strip.
If the iMac doesn't reboot on its own, reach around and press the power on button.

I'll bet that my "dumb, easy" way works just as well as the more expensive fix, for years to come.

 

[hobowankenobi]

If it is a CMOS battery issue...the date and time will be wrong (set back to defaults). If you don't see that, I would not disassemble it. I have seen this on quite a few Macs, but typically they have not had a graceful shutdown.

Questions:

Are you sure it was powered down completely before it was unplugged?
Why are they unplugging?

 

[retta283]

I have a 2006 iMac (ancient, I know) with a failing CMOS battery that exhibits this same behavior. Immediately after connecting the cord it powers up on its own. It's the only Mac I've owned that does this. Otherwise the machine works perfectly; I have always been curious why this is.

Note that a low CMOS battery will not always be self-evident, sometimes it takes a while for the time to either reset or get stuck. CMOS batteries don't always cause a complete reset until they have totally died. I have Windows machines that are years behind, but are correct to the date they were last powered up. it's just that when it's not connected to power it stops counting.

 

[user1234]

I have had this issue before on a machine - the CMOS battery was dead on the logicboard. So you're looking at a hardware problem. Fixable, if you can take the machine apart to replace it.

I don't see any other signs of CMOS battery issues. Time does not reset, and apart from this there are no issues.

My guess is a failure of the power-on button. It's "stuck in the on position".
Don't bother taking it apart.

Use this "Fishrrman dumb as they come™" solution:
- Buy a cheap power strip with several outlets on it
- Plug the iMac into the power strip (perhaps some peripherals, too)
- When your parents are done using the iMac, choose "shut down" from the menu as they usually would
- Wait for the shutdown, and "the spontaneous reboot" sound.
- At that point, IMMEDIATELY REACH DOWN AND TURN OFF THE POWER STRIP.

When they're ready to boot the iMac again, just reach down and TURN ON the power strip.
If the iMac doesn't reboot on its own, reach around and press the power on button.

I'll bet that my "dumb, easy" way works just as well as the more expensive fix, for years to come.

It's definitely not the power button. It works just fine. After shutting the computer down it stays off unless unplugging and plugging back in and using the power button it starts as usual.

If it is a CMOS battery issue...the date and time will be wrong (set back to defaults). If you don't see that, I would not disassemble it. I have seen this on quite a few Macs, but typically they have not had a graceful shutdown.

Questions:

Are you sure it was powered down completely before it was unplugged?
Why are they unplugging?

Time and date is not reset so I would be surprised if it was the battery.

They have it on a power strip together with their phone chargers and when not using any of it they turn off the power. Probably a generational thing about saving power.

I have a 2006 iMac (ancient, I know) with a failing CMOS battery that exhibits this same behavior. Immediately after connecting the cord it powers up on its own. It's the only Mac I've owned that does this. Otherwise the machine works perfectly; I have always been curious why this is.

Note that a low CMOS battery will not always be self-evident, sometimes it takes a while for the time to either reset or get stuck. CMOS batteries don't always cause a complete reset until they have totally died. I have Windows machines that are years behind, but are correct to the date they were last powered up. it's just that when it's not connected to power it stops counting.

I'm still think it would show some other signs if it's so bad unplugging it for 20 seconds makes it start when plugged back in again. But maybe not?

 

[TwoH]

I don't see any other signs of CMOS battery issues. Time does not reset, and apart from this there are no issues.

If you are connected to the internet then it will display the correct time.

 

[retta283]

Time and date is not reset so I would be surprised if it was the battery.

As mentioned above, if you're connected to the internet the time/date automatically syncs. You can turn this off in settings or just disconnect the internet and restart if you'd like to test that further.

 

[user1234]

If you are connected to the internet then it will display the correct time.

As mentioned above, if you're connected to the internet the time/date automatically syncs. You can turn this off in settings or just disconnect the internet and restart if you'd like to test that further.

That's a good point. I'm not sure if NTP runs before the OS is loaded or not, but it's easy enough to test. Will do that as soon as possible.

 

[hobowankenobi]

If you are connected to the internet then it will display the correct time.

The last time I tested it, automatic time takes a bit to kick in. Not instantaneous.

One could also disable the setting to test too.

 

[user1234]

I got a chance to do some testing and turns out the CMOS battery is bad. When unplugged for a few hours then turned back on with no network the time is running behind. If left long enough the time is reset to 0:00 January 1st 2023 (not 1970, so I guess they modernized that).

When the network was connected again the time was set correctly in less than a second which is impressive. Especially compared to the competition from further north where it can take hours.

So now I have that to take care of

 

[hobowankenobi]

Good to know. Thanks for reporting back!