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You are here: MacNN Forums > Hardware - Troubleshooting and Discussion > Mac Desktops > help: iMac not booting from bootable external disk

help: iMac not booting from bootable external disk
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Jul 10, 2014, 03:33 PM
 
Hi All,

I have a troublesome iMac that is refusing to boot from a bootable external disk, and I'm hoping for some guidance.

This is an early 2008 24" iMac with a chequered past. Just after the warranty ran out (like a week after, sans applecare), the internal drive died. My local computer store (from which I bought it) replaced the drive and ever since it's had an overheating problem (fan constantly on, and the machine spontaneously going to sleep to, likely, cool down). The store went out of business before I could get them to deal with the issue, so I learned to live with the problem.

Now the internal drive has died again, and I don't want to crack the Mac to replace it, rather I've decided to just boot from an external Firewire 800 drive (a WD 2TB drive that I've put into a Macally G-S350SUAB external case). I booted into the TimeMachine backup drive, cloned the complete backup to the external drive, and designated it as a startup drive. The Mac restarts, chimes and...nothing, just a white screen (no Apple appears, no wagon wheel). I left it on the white screen for over 30 mins, just in case.

I've confirmed the external drive is bootable in Disk Utility, and I've even hooked it up to the iMac via USB and Firewire 400, all give the same problem: white screen after chime.

I'm about to wipe the external drive (while attached to another Mac) and install Mavericks on to it from scratch (Lion is what was installed on this iMac before, so the boot from TimeMachine backup gives me only that option, but every time I try to install it I get a "This item is temporarily unavailable". Grr).

Any insights into what more I can do here? I'm willing to learn how to crack this machine open and pull the dead internal drive, as I'm thinking that it's interfering with the boot process (not sure how, but gotta remove all variables). Not sure what else to do though, and cracking it myself is a big ask (I hear that these machines are a pain to open and close).

Thanks in advance for any help!

Chas
     
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Jul 10, 2014, 04:41 PM
 
Take a look at your external drive with Disk Utility. Select the drive icon in the left pane. Then look at the info at bottom of window. What does it say after "Partition Map Scheme"?

It sounds like you didn't partition or format the external, just cloned across. Many new drives come with Master Boot Record partition schemes to be friendly to Windows machines. You need GUID partition scheme in order to boot from that drive.

Regarding the fan use, they probably didn't put back a drive temp sensor. If you ever replace the internal drive, they can probably fix the fan problem at the same time. You shouldn't have to live with shutdowns and constant fan operation.
     
chasg  (op)
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Jul 10, 2014, 06:23 PM
 
Thanks reader50, for the response.

Your suggestion is a very good one, but I formatted the disk to Mac OS Extended (Journaled) before starting the whole process (so it already has a GUID partition scheme, confirmed in Disk Utility). Rats, I was hoping for such a simple fix!

And as far as the fan goes, I'll point that out (and if I crack it myself, I'll look up where the sensor should be). Very much appreciated, it'd be nice not to have to endure such a wonky machine! Now, if only I can get the thing to boot up...
     
chasg  (op)
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Jul 10, 2014, 06:43 PM
 
Hmm, an extra development: I installed a vanilla copy of Mavericks on the external drive, and tried to boot my laptop (2.4 GHz Intel Core 2 Duo) from it. The laptop wouldn't boot from it, and reverted to the internal drive.

Argues for something wrong with the external drive. Given your advice, I'm pretty sure that it's formatted correctly, and Disk Utility says that it's bootable. So now what? I'm at a loss, I can't troubleshoot the iMac unless I know the external is acting the way it should, but it's not :-(

I have an old firewire 800 external I could bring in, so I can eliminate the variable of a problem with this new external drive I'm attempting to use (this old fw 800 drive is only 120GB, so I can't use permanently on the iMac, but it'll suffice for testing).

The saga continues.
     
chasg  (op)
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Jul 11, 2014, 07:18 AM
 
$%^&*!! Installed Mavericks on my 120GB FW80 drive, and it's booted the ailing iMac successfully. Dammit!!

This means that the expensive FW800 case plus 2TB drive, which should boot the iMac, is faulty somehow. I am really annoyed (all that time and expense adds up to grrrr).

Now I need to troubleshoot the brand new case and drive. Double-grrrr.

At least I know that I can boot up the iMac from an external drive :-/

Thanks again for the input, I really appreciate it.
     
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Jul 11, 2014, 07:22 AM
 
Maybe it actually means that when you cloned the backup it didn't clone the way you expected. I haven't messed around with moving/cloning TimeMachine backups, but is it possible that you actually just copied the backup to the external drive instead of restoring it there?

Glenn -----OTR/L, MOT, Tx
     
chasg  (op)
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Jul 11, 2014, 07:34 AM
 
It's a good question, but I used the recovery drive's offered cloning method. I've successfully done this twice before, but I was willing to consider that it didn't work this time.

So I did a vanilla install of Mavericks on the Macally G-S350SUAB enclosure + 2TB drive combo, and I've confirmed that it won't boot either this ailing iMac or my Macbook Pro. Deeply annoyed with this purchase (FW 800 enclosures are pretty expensive these days, I wish this iMac was newer and had USB 3, it all would have been so much cheaper!).

Thanks for the input, I really appreciate it.
     
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Jul 11, 2014, 08:03 AM
 
I have a suggestion for troubleshooting the new drive. Since this is on Mavericks you can use createinstallmedia. TO BE CLEAR, THIS WILL DELETE ALL THE DATA ON THE EXTERNAL.

Do this:
1) download the Mavericks full installer from the MAS.
2) rename the external drive "trouble"

3) Copy and paste this EXACTLY into the terminal. THIS IS ONE LINE.

sudo /Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia --volume /Volumes/trouble --applicationpath /Applications/Install\ OS\ X\ Mavericks.app --nointeraction

4) Wait, probably about a half an hour. When done, the media is a vanilla Mavericks installer. If it boots, then the hardware of the drive is fine, and there was something wrong with your clone.

createinstallmedia fixes boot partitions, makes an emergency install partition, and does everything to make that external a vanilla installer. Sure, it won't have your data, but this will test the ability of the disk to be a boot disk.

Also, this works GREAT for making USB flash drives a Mavericks installer.
     
chasg  (op)
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Jul 11, 2014, 08:25 AM
 
That's great info, many thanks! I have a nice, large, USB drive that I'll be using your info with, just not sure it's relevant to my immediate problem at this time: I've eliminated the Time Machine clone as a variable.

Not sure if you read my 12:18pm post from today: I wiped the new case + drive and installed vanilla Mavericks, and the new case + drive won't boot Macs, but an old FW800 drive, also with vanilla Mavericks, will boot Macs (both the ailing iMac and my Macbook Pro). Do you advise I still work through your instructions above? (what variable would I be eliminating?)

Thanks again for the info.

Cheers!

Chas
     
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Jul 11, 2014, 10:43 AM
 
Didn't MISS it per se, just read it too quickly. The vanilla mavericks install on the wiped drive part is the part I apparently glossed over...

Good that the info helped/will help, though!
     
chasg  (op)
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Jul 11, 2014, 10:55 AM
 
Yeah, it's a wall of text (tech problems always are! :-) The info you did pass on was very useful though, chalk it up to serendipity.
     
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Jul 13, 2014, 06:14 AM
 
Just migrate data from the time machine backup to the Mavericks drive and if its happy like that clone it back to the firewire 800 case.
I have plenty of more important things to do, if only I could bring myself to do them....
     
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Jul 13, 2014, 01:29 PM
 
Originally Posted by chasg View Post
$%^&*!! Installed Mavericks on my 120GB FW80 drive, and it's booted the ailing iMac successfully. Dammit!!

This means that the expensive FW800 case plus 2TB drive, which should boot the iMac, is faulty somehow. I am really annoyed (all that time and expense adds up to grrrr).

Now I need to troubleshoot the brand new case and drive. Double-grrrr.

At least I know that I can boot up the iMac from an external drive :-/

Thanks again for the input, I really appreciate it.
Man, chasq, seems like you are going through hell! There have been quite a few excellent suggestions, but I think I have a couple of more that may just help you.

First of all, since you are able to boot from the small (capacity wise) external drive, are you able to take a look at the internal drive inside your iMac?

Secondly, while Disk Utility is a good tool, you might want to consider something more "robust", like Disk Warrior or Tech Tool Pro. If you have either (or both) of those on your external drive, you might want to use them to look at both the internal and external (2 TB) drives.

Third, about 2 months ago, the 500 gig Seagate drive I had inside an external case (came that way; it also has two Firewire 800 (and two USB 2.0) ports) all of a sudden went bad. After trying numerous things, I decided to replace the drive, and I did just that with a 1 TB Seagate drive. That worked real well, and I am even able to boot from the Super Duper Backup of my internal drive on my Mac Mini (and also the one in my Mac Book Air) that is on that drive. (I was fortunate that the case was OK, as were the ports, as I had previously purchased a somewhat expensive Apple Thunderbolt-to-Firewire 800 connector, and I wanted to continue to be able to use it with my Mac Book Air).

It does sound like the internal drive inside your iMac is "bad", which means you'll need to replace it if you want to continue to use the machine. But (fingers crossed!), maybe Disk Warrior and/or Tech Tool Pro will show something different. The fan issue, though, is potentially more troublesome.

Good Luck!
( Last edited by akent35; Jul 13, 2014 at 01:46 PM. )
     
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Jul 15, 2014, 03:35 PM
 
Any further progress, chasq? I am certainly curious how you are trying to resolve this issue, and if you are making any progress.
     
   
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