iMac24 switches itself off after a few seconds


There is a problems with iMac24. As soon as you press the power button it switches itself on, runs for a few seconds and immediately switches itself off. There is some importan data which I would not like to lose.

Could you please help?

Many thanks
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It may be the power supply.  They are replaceable, but I need the exact model number in order to tell you where to get it and what it will cost.

However, if you would rather get a new machine, the drive can be removed from you iMac and into a USB enclosure so you can plug it into another Mac and get your files.  You cannot read a Mac disk from a Windows PC.
Thanks for asking your question with Experts Exchange.  

Whenever you are experiencing power management issues such as you are with your iMac 24"
I would recommend you take some basic troubleshooting steps before resorting to going directly to the hardware. Although I do agree, that the power supply can be a catalyst for the boot up/sudden shutdowns, sometimes  the issue may be with the main logic board, in association with the power supply.

 Therefore, a reset of the micro controller,  which governs power functions of the main logic board and the power supply as well as all power management issues, may just need a "reboot" in order to resume functioning properly and allow the iMac to resume normal boot up processes, while remaining on, instead of just shutting off on you.

So here are a few procedures I would recommend you try:


• With your iMac shutdown of course, you will need to perform what is called a PRAM reset (Parameter RAM)

• Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously .

• Turn on the computer.
• Press and hold the Command-Option-P-R keys. You must press this key combination
  before the gray screen appears.

• Now, hold the keys down until the computer restarts and you hear the start up sound for
 the 2nd time.

• Release the keys and allow the iMac to start up.

If this does the job, great, however, if it does not then proceed to the next procedure.

-------------------------------------------------------------------------------------------------------------------------------------SMC RESET-

The System Management Controller is an integrated circuit (computer chip) that is usually on the logic board of your Intel Mac computers.

It  is responsible for power management of the computer. It controls backlighting, hard disk spin down, sleep and wake, and some input/output as it relates to the computer sleeping

• Shut down the computer.
• Disconnect all peripherals except for the power cord
• Once you have disconnected all device connections
  unplug the computer's power cord.
• Press and hold the power button for 5 seconds.
• Release the power button.
• Attach the computer's power cable. (do not connect any other peripherals yet)

• Press the power button to turn on the computer.
 If the iMac starts up and boots to the main desktop, interact with your Mac for about
 10-15 minutes or so, to see how it responds.

If this works, excellent. However if at any time you get the shutdown again,
you are definitely experiencing a hardware issue with more than likely the power supply.

Depending on your model of Intel iMac, 24", you will need to either source the power supply or take your iMac into your local Apple Retail Store Genius bar or Apple-authorized service center and have a diagnostics performed to at least determine if the issue is a power supply, or main logic board issue, or something else.

Just for your reference, I have taken the liberty to provide the store locator links to your local Apple Retail store as well as a general store locater for locating any local Apple Authorized Service center in your area.

Apple Retail Store (Genius bar)

Apple Authorized Service Provider

For sourcing your power supply, here is an online Apple vendor I like to refer some of my clients to, due to their comprehensive Apple parts database and parts availability:



I hope this information proves helpful.



RemapAuthor Commented:
I shall go ahed with the troubleshooting steps. Thanks for that. In the meantime the model of the iMac is A1225
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RemapAuthor Commented:
The troubleshooting steps did not help.
I did
# start up the Mac while holding the CMD(Apple)+S keys
# at the black window that appears, type fsck -f and press enter

the results are:

**checking catalog file
  Invalid sibling link
**volume check failed
/dev/rdisk0s2 (hfs) exited with signal 8

Any idea?

Is the hard drive or OS bad?
RemapAuthor Commented:
I tired a new power cord to no avail.

RemapAuthor Commented:
Could this really be the OS issue rather than the power supply?
Did the iMac stay on while you were running the diagnostics?  If so, my guess is it's related to the hard drive or power supply and not the OS itself.

About how long does the machine run when you boot it before it shuts down?
Can you boot from the Apple recovery CDs?  If so, how long does it stay on then?

If it DOES boot with the CDs, try running Disk Utility (repair permissions) on the hard drive from the CD.
RemapAuthor Commented:
Yes the Mac stayed on while I was running the diagnostics! When I power it on it runs for no more than 20sec.

I have not got the Apple recovery CDs.
RemapAuthor Commented:
What do you think would be the logical steps to resolve the issue considering I have not got the recovery CDs?

I asked earlier, but can you give me the model #.  What version of OS X were you running?
Thanks for your update.

I see what noted is that you see this error when you ran the Single User mode
using the fsck -f command:
"**checking catalog file  Invalid sibling link(4,903)**volume check failed/dev/rdisk0s2 (hfs) exited with signal 8"

This "Invalid sibling link volume check error" is an indication of an issue with your
Mac OS X volume's catalog B-tree within the Mac OS X directory.

You see, Mac volumes keep their records in the form of a catalog file. This catalog file is  structured in a B*-tree formation. So to locate a file or directory, the system has  toscan the complete Catalog B-Tree and if there are any errors with any of the nodes or the tree itself, this may require reformatting the of the Mac OS X volume to correct.

Unfortunately with an error like this, Disk Utility will not be enough to resolve that issue, but a more robust Mac HD repair/rebuild utility application like Disk Warrior 4.2 usually can do the job, because it has the capability of repairing a damaged Catalog B-Tree errors which is the underlying cause of errors such as "Invalid sibling link" and "Invalid structure" errors

Here is the Link for this powerful HD repair software: DIsk Warrior 4.2


As I had mentioned before in my previous answer, if the shutdown persists, especially after your iMac has only been on for 20 seconds, that is definitely a hardware issue a very likely, it is with your power supply.

 A bad main logic board would not allow you to even get as far as you did when you used the Single User mode procedure, so I would hope for a bad power supply any day if this has to be a hardware issue as it is appearing to be.
For your iMac 24" model  A1225 - Here are the specs for your model:
Marketing# MA878LL A
iMac 24" (Mid-2007)
24" Intel Core Duo 2.4Ghz (or 2.8 Ghz) 1G RAM /320 HD /SuperDrive-DL

So the part # for your iMac 24"'s Power Supply, is 661-4183

My apologies about the link above in my first answer. I am not sure
if it did it to you, but when I clicked it, I was directed to an incorrect webpage.

So here is that same link with the correct page link for the power supply:

Link: iMac 24" (A1225) Power Supply
Even if you should have to replace the Power Supply, I would still recommend you invest in a copy of Disk Warrior 4.2, just to have nearby in the event you have to use it, once this power issue with the power supply is resolved.

Let me know if this helps.



Sorry!  I missed your post with the model number.
RemapAuthor Commented:
Apparently the iMac is from 2008 and it is 24"/3.06Ghz/2x1GB/500Gb
So I am not sure now if the power supply part is the same as posted above 661-4183. Thanks for recommending Disk Warrior.

One interesting thing to mentioned which I am just doing on the iMac. I am running a Techtool diagnostic CD disk to diagnosoe the source of the issue. The iMac stays on during the whole test.
What I did was I pressed OPT key and chosen to boot from CD. The iMac behaves ok. Does this mean that we can rule out a problem with a power supply?

I am just checking a hard drive for bad sectors....

but get Disk Warrior in the meantime...
RemapAuthor Commented:
iMac is from April 2008
It's still possible for it to be a hardware error, but the corrupted disk is also a possibility.  Disk Warrior is the best test you can run at this point.  Hopefully, it will fix the problem.

Let us know!
RemapAuthor Commented:
I let you know when the surface scan is finished. In about 2 hours.
RemapAuthor Commented:
Ok the results are :

Hard drive is ok. No bad sectors. However, there is an issue with the Volume Structures. The result says Validation Error Encountered. Allocation File (Bitmap). It is Mac OS X 10.5.5 build 9F33.

Can I rebuild the Volume Structure without loosind data.

All the time the iMAc was on, more than 2 hours in total. So it would again confirm that the power supply is not hte issue.

What are your thoughts?  
RemapAuthor Commented:
Problem solved.
Techtool rebuild volume structures solved the problems
Excellent update Remap,

This means the Catalog B-Tree has been rebuilt by Tech Tools Pro which of course fixes all nodes and links as well.

In regards to your question about your iMac 24"/3.06Ghz/2x1GB/500GB
the correct part number if you were to order a Power Supply, would be: 661-4665

Tech Tools Pro is also another good Mac utility. So with this application, as you can see from the proven results, there is no need at this time for you to invest in Disk Warrior, unless you would like to have a copy of that software for your own reasons.

Thanks for allowing us to assist you!

Best Regards,

RemapAuthor Commented:

I still need you help.
The iMac will not boot. After 3 days since I managed to resolve the boot up issue it is doing it again.
Is does not switch itself off after 15 sec. But it does boot to OS. I found the installation discs and tried to run disk utility but it could not repair the volume.

Is there any way I could recover the data and perform the re-installation of you have other ideas?

Many thanks for helping
Thanks for the update.

Based on your last reply, I am not sure if you are saying the iMac does or does not boot to the OS. If you are stating that the iMac does not shut itself off as it used to, but you are still unable to boot to the operating system, then you very well may have a corrupted volume on your hard drive.

Your best recourse in a case like this would be to perform an Erase and install. In order to safely recover the data from the hard drive however, you would need to perform a Target Disk Mode procedure,  if you have another Mac computer, that you can hook up to via a Firewire cable to your iMac.

 This procedure, would make your iMac the targeted disk drive (because of course that is where your desired files are) and the other Mac would be the host computer. If you are able, with the host computer to get a hard drive image from the affected iMac to appear on  the host's desktop, then you can use an image cloning software like Super Duper! or Carbon Copy Cloner, to clone an image of the hard drive or image a copy of your user's home folders.

If you do not have another Mac to perform this procedure, then you may just want to consider Disk Warrior, as it is one of the best Mac utility applications for rebuilding damaged Catalog B-tree errors. I understand you tried with Tech Tools Pro to resolve that error and by all appearances, it look like it did repair your hard drive, until you recent reply which suggested otherwise. From my standpoint as a professional Mac technician, I would recommend you have both utilities, because I do and when one cannot do the job, the other one usually does, which is why I keep both in my Mac software tools library.

Disk Warrior's biggest strength, which I believe  is what makes it one of the best for repairing and even eliminating Mac OS  X volume errors, is its ability to repair and rebuild damaged or corrupted volumes.

This is my recommendation, and I speak from experience. Otherwise, if Disk Warrior does not do the job, you may very well have a corrupted hard drive.

In the meantime, while you are thinking this over, I would recommend you try this Unix-based command line procedure ,to try to diagnose the integrity of your hard drive as well as attempt to repair the affected volume:


Start up your computer in Single-User Mode to reach the command line by doing this:
•Make sure your Mac is shutdown.
• Reboot your Mac
• When Mac  starts up, press the Apple Command key+ S Key
- A black screen, with white text appears
• At the command-line prompt type:   /sbin/fsck -fy
• Press Return.

--fsck will run through a series of tests and will return information about your disk's use and fragmentation. When completed, it will display this message if no issue is found:

    The volume (name_of_volume) appears to be OK

If fsck found issues and has altered, repaired, or fixed anything, it will display this message: --FILE SYSTEM WAS MODIFIED--

Important: If this message appears, repeat the fsck command you typed at the beginning, until fsck tells you that your volume appears to be OK (first-pass repairs may uncover additional issues, so this is a normal thing to do).

• When fsck reports that your volume is OK, type reboot at the prompt and then press Return.

• This last command after completing the fsck process, is going to attempt to boot your Mac to the main desktop.

 If you cannot get through this process completely, this means you do either have a damaged or corrupted Mac OS X volume, that is too damaged to be repaired and must be erased, or r possibly even a damaged hard drive.

Whatever  option you decide to go with from what I provided you above, will be per your decision and only your decision, but I want to make sure you have as many effective options to entertain as possible.

Let me know if you have more questions or concerns based on the recommendations and procedures, I have provided for you in this post.




RemapAuthor Commented:

When I try to Start up  computer in Single-User Mode to reach the command line I get the the following errors:
could not open file 'mach_kernel'
Error loading kernel 'mach_kernel'  (0xa)

Sometimes I can not even initialize the Single-User Mode. The screen remians white and nothing happens.

When I switch the computer on and let it boot it does not shut itself down as before, however I get the folder icon in the middle of the screen with a question mark in it. The folder icon is blinking. Previously I was able to choose the booting source by pressing C on the start of the iMac. Now it seems that the hard drive is not being picked up.

I look forward to your comments
RemapAuthor Commented:
When I try to Start up  computer in Single-User Mode to reach the command line again I got as far as
'AppleIntelCPUPowerManagment : initizlization complete
AppleAHCIDiskQueueManager ::setPowerState(0x4640c00, 2 -> 1) timed out after 129556  ms

I have got the DiskWarrior 4.2 but I can not boot up from it.... :-(
RemapAuthor Commented:
Further to starting up in Single-User Mode...
disk02: I/O error
RemapAuthor Commented:
now I am gettting 'Invalid sibling' It should be 33 instead of 31
RemapAuthor Commented:
I does not make how many times I start iMac in Single-User Mode to repair the hard drive I either get the error of:

'Incorrect block count for file asl.db ( It should be 33 instead of 31) Invalid sibling link
disk02: I/O error Invalid sibling link
Thanks for being so diligent Remap.

You are not alone with this issue with your hard drive, as it appears your Mac OS X volume is too damaged for Tech Tools Pro or Disk Warrior to work.

What I would like you to review is this link below, for an Apple Discussions forum which addresses the disk02: I/O error and Catalog-B-Tree errors.

Cannot boot from hard drive

Let me know if this information helps.

I will be watching for your next comment and thanks so much hanging in there thus far.


- Mactechtrainer

RemapAuthor Commented:
Thank you for your patience and helping me out.

I did run AHT three time times and found no problems. I am trying to recover the data from the drive to erase the volume, however I am unsuccessful usind Disc Utility for the iMac OS .
When I try to create an image the software says 'Unable to create..... (error -61).

I have got the other Mac. My Mac environment is very limited. I have OS discs, Tech Tool dics, Warrior Disc which does not boot up.

Is there any way to perform the reinstallation of the OS without losing the data?
If not what would be a good way to recover the data? I would like to recover at least 'Users' folder
I would also like at the later stage when the OS issue is resolved install Windows 7 via Boot Camp.
Do you see any weaknesses of doing that?

Many thanks for great help.
No worries Remap, glad to help.

I do not read you indicating that your iMac is not shutting off, so I am glad to see that.

By the looks of it, our focus is going to have to be on this hard drive. I am also glad you have confirmed that you do have another Mac, because I was going to ask, have you tried the Target Disk Mode procedure I suggested to you in one of my earlier posts?

That would be great to use the Mac you have as the host computer and the iMac with the affected hard drive as the targeted disc, so you could remove your Home folders (Users folders), safely to your host Mac, provided it has enough space.

Have you considered trying that method, or have you already done so?

RemapAuthor Commented:
I am sorry I made a mistake in my last post. I must have been tired. I HAVE NOT got another Mac. Hence I do not exactly know which path to follow to recover the data before the reinstallation.
RemapAuthor Commented:
Any more comments please....?
Hi Remap,

I have checked into your issue a bit further and  I have really been taking time trying to find the best alternative solution for you.

Considering what has been attempted so far, the option I have should not be an expensive alternative, but you will have to pay for it, if you want to save your data.

What I would like to suggest:

From this point, my advice would be for you to take your iMac in to your local Apple Store Genius bar or Apple-authorized service provider and see is a diagnostics and repair can be performed on your iMac and hard drive. If  necessary (as these service centers will have the resources), you may need to purchase another internal 3.5 hard drive (500 GB or higher) and have them perform a data transfer to retrieve all of your important files from your Home Folder(s) from the affected hard drive.

That is one way to try and resolve this issue, because this definitely has the appearance of a hardware issue for sure.

Now if you want to take a DIY approach, you can try this.

1.)Look into investing into another internal hard drive for your mac
2.) Purchase an low cost USB  external enclosure for  your 3.5"" hard drive
3.) Take the affected internal hard drive out of your iMac
4.) Install the new internal hard drive into your iMac
5.) Take the affected hard drive and connect and put into external USB enclosure.
6.) Install the latest Mac OS X version you have, on the new internal hard drive
7.) Once the installation is successful and you are able to boot to a normal desktop again,
run all updates.
8.) When completed, take and connect the USB hard enclosure (now containing your
     affected hard drive) and connect to your iMac.
9.) See if you are able to connect and access the files of the affected hard drive via your iMac
10.) If you can, then use Super Duper! or Carbon Copy Cloner to image your Home folder onto
your new internal hard drive.
11.) If you are able to do this successfully and can access those files, you should then get rid
of that affected hard drive, recycle it, or whatever you need to do with it.
12. When you are ready, you can invest in another 3.5 internal hard drive and place that in the 3.5 USB
external hard drive enclosure and now you have a second (external) hard drive.

Now remember, these are only only suggested processes, but they are practical given your current technical issue.

So let me know if this helps.

I will be watching for your next post.



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RemapAuthor Commented:
Many thanks for coming back to me.

If I go for the DIY option and put the affected hard into the enclosure and manage to transfer the data why to skip the hard drive? The hard drive did not seem to have bad sectors. Only Volume Structures seemed to have issues. My understanding of this situation is that if the data is recovered I could just format the hard drive and use it as a backup drive in the the enclosure.

Would you agree with me?

RemapAuthor Commented:
Is the hard drive for iMac24 is 2.5" or 3.5"?  I know that the capacity is 500GB. Could I just get any 500GB SATA II hard drive of the right size obviously?
I have not yet had the chance to open the iMac to check for the hard drive.

Please let me know ASAP.
RemapAuthor Commented:
Would any SATA enclosure be fine for the original hard drive?
Hi Remap. Sorry for the delay, I work full time for a very busy computer firm and so I have not had a chance to reply to your posts, as fast as I normally have from last week, so my apologies about that.

 To answer your questions however:

In one of your recent posts you stated:
"If I go for the DIY option and put the affected hard into the enclosure  and manage to transfer the data why to skip the hard drive? The hard  drive did not seem to have bad sectors. Only Volume Structures seemed to  have issues. My understanding of this situation is that if the data is  recovered I could just format the hard drive and use it as a backup  drive in the the enclosure."

I only suggested you get rid of the affected hard drive, if after you are able to successfully extract and transfer files to the new hard drive, but are not able to reformat the affected hard drive so it could be used again. It would be then you may want to look into another hard drive to replace that drive. Then you could put the 2nd new hd into your enclosure and use it as a backup. That is what I was working to explain to you.

 I do see I left that detail about re-using the affected hard drive again. But hey, if it works fine after the data is extracted off of it and you  reformat it with no issues, that is fine too, because
that would save you from having to get another drive for the enclosure. Trust me, I am all for whatever works here to get your Mac back up with this hard drive and data issue.

One more bonus software for you to consider as well as an option to
 imaging your hard drive (if I have not suggested it already):

Check out: File Salvage 7.0 from Subrosasoft
(Arguably one of the best data recovery software applications, I have ever used for Macs)

Regarding the Sata Drive and the 3.5 SATA USB Hard Drive Enclosures:
The Intel iMac 24", takes a standard 3.5" drive, so you would need to look into a 3.5"  Sata USB enclosure. And yes,  as long as the hard drive is a Sata drive, you can use it. Apple does not maufacture hard drives, they purchase hard drives just like the other large computer manufacturers.

Here is a good start page via Remap, if you want to get an idea what they look the type of enclosure you need looks like and the various price points of this item.

3.5 Sata USB Hard Drive enclosures

Now in order to remove your hard drive from your iMac, you will need to research online for a "Take Apart manual for the Intel iMac 24", as you will need to have that type of guide in order to safely and correctly remove the affected hard drive from your iMac.  You can always perform a Google search, or check out websites: or and see if either of these great websites can provide a Take Apart guide for your model.

I hope this additional information will provide you the path to the full resolution which you have been seeking Remap.

Thanks for being so patient and asking great questions!


RemapAuthor Commented:
Hi there,

Thank you for getting back to me. I made so progress sice our last chat.

The affected hard drive happened to have a lot of bad sectors. So it was not ok. The iMac has got a new hard drive installed and OS 10.5.2 Leopard with all the updates to 10.5.8.

If I may ask to give me a piece of advice. In OS 10.5.8 now on the iMac bootcamp assistant has got version 2.0

I would like to install windowds7 on the iMac and need to update bootcamp assistant to the latest version 3.1.

I have downloaded the latest version but when click on it to run it I get a pop up windows with a lot of scrambled content.

Do I have to update the OS to 10.6 Snow Leopard or I am doing somethig wrong?

I would appreciate your comments.

Hi Remap,

No you are doing anything wrong, it is just a matter of compatibility.

Yes, you do have to update to Snow Leopard in order to use Bootcamp 3.0-3.1.

That version of Bootcamp was made for 10.6 or higher, so if you want to install Windows 7 on your Mac, you would need to purchase a copy of Snow Leopard.

The good news is, because you are currently a Mac OS X 10.5 Leopard user (10.5.8 to be exact), you can purchase a copy of Snow Leopard for only $29.00USD.

Purchase Mac OS X 10.6 Snow Leopard

Get a copy of 10.6,  Bootcamp 3.1 is yours for the using!

Glad to get your previous update Remap. I know you have worked hard to get to the end of the
journey of this issue.

RemapAuthor Commented:
Many thanks for all help, patience and valuable advice.
I have installed Snow Leopard 10.6 on the new HDD installed on the iMac. Then managed to retrive the data.
I also installed Windows 7 Ultimate on the iMac so have dual boot.

The whole issue with iMac and your in-depth Mac knowledge were good experience...
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