GA-Z77X-UD5H doesn't reach bootloader

[MTB]

I am running Mavericks 10.9.0 on a Gigabyte GA-Z77X-UD5H motherboard with pretty standard hardware. I built this hack with Mountain Lion about a year and a half ago and haven't had any issues upgrading.

Today I decided to upgrade to 10.9.2 so I downloaded the standalone installer and repaired permissions as per Stork's instructions at http://www.tonymacx86.com/407-os-x-10-9-2-update.html. Diskutil found a bunch of issues, so I restarted before moving ahead with the update. On that restart, disaster struck: refused to reboot -- I don't even reach the bootloader.

So here's where I am stuck:

• When I let it boot to the default drive (P0: 128 GB Samsung 830 SSD), immediately after the motherboard splash screen it goes to a black screen with the spinning ASCII characters in the very top left, though they only spin for a second before freezing, either with an underlined \ or |.
• Naturally, my first thought was to boot from my Unibeast USB drive. No dice -- exact same behavior. I am not sure how to tell if that is because it is hitting the same issue on the second drive, or if that it is not finding a bootloader on the USB drive so it is just reverting to my primary SSD.
• I can enter the BIOS and force it to boot to my secondary SSD (P1: 64 GB Samsung 830 SSD), which happily boots up Windows. Joy.

My next step will be to recreate the Unibeat USB drive in an attempt to get that to work and hopefully use that to identify the problem and repair the bootloader.

• Have any of you encountered an issue like this? Did I cause it by repairing permissions?
• Is there any way to get more information about exactly what is causing the issue before I reach the bootloader?

Thanks for the help!

 

[MTB]

Okay, recreating the USB drive didn't help. I am completely dead in the water, can't get anything Mac-related to boot.

On one hand, it feels like it must be hardware because it crops up so fast; from the time when I select the boot drive (either SSD or USB) it takes less than a second to "freeze" with just the one character and blinking line in the top left of the screen. On the other hand, Windows is happy enough to boot.

Can anyone shed any light on this?

 

[MTB]

Update: Tried the boot0 fix, no luck. Ugh.

 

[MTB]

Duplicate post

 

[MTB]

SOLVED! Well, partially.

In addition to my two bootable SSDs, I also have two 2 TB HDs, one for my files, the other for Time Machine. If I disconnect the internal Time Machine HD, everything boots normally.

It turns out that there are a bunch of people who have posted about Chimera behaving oddly when a large Time Machine HD is attached. Their experiences are all identical to mine: works fine but then breaks seemingly unprovoked. Unfortunately, no one seems to have a fix other than to erase the drive and start over.

If anyone can tell me how to fix the issue without nuking the drive, I'd appreciate it.

 

[pisomojado]

This is terrifying! If I give up on trying to upgrade to Mavericks, will I avoid this problem? Or does it affect 10.8.5 as well?

 

[MTB]

It turns out that this issue is unrelated to Mavericks -- people began complaining of it before Mavericks was released, at least as far back as 2011.

I wouldn't worry too much about trying to avoid it at this point; we don't know enough about why it happens. Enough people have had it to verify that it is a real issue, but not so many that anyone who really knows how to fix it has bothered to take it on.

At least it has now been identified, so that if you find yourself in this situation you have a relatively simple workaround.