iMac not waking up from sleep after Yosemite upgrade

The help links for the problem suggest that if the problem goes away with the external drive disconnected, it's the fault of the drive manufacturer!? Seems unlikely ... passing the buck?? I have TB LaCie drive and TB Buffalo drive.

I guess I'd find that a bit more plausible had the problem not started immediately after the Yosemite upgrade.

Sent LaCie a trouble ticket. Let's see what they say. Problem not happening with my Thunderbolt Buffalo drive connected. Since my LaCie drive is my Time Machine drive, does Time Machine operate during Sleep mode under Yosemite?? Part of the problem??

Well, just as another data point, I'm having no problem using my two smaller rugged TB drives (also LaCie), and don't use any of my drives with Time Machine. Interested to see what LaCie comes back with.

Heard back from LaCie and tried their suggestion. Appears to have worked so far (all day!).

Hope that does the trick! I'm gone for the holidays so I won't be able to try it on my machine for awhile. Thanks for the followup!

Follow up ... woke up to no problems. iMac woke up instantly.

Note: Didn't do "Target Disk Mode" ... just selected "Mackintosh HD" and clicked Restart.

Have a good holiday!

Just come to use my Mac and ..... nothing.

So for me LaCie's advice has not worked. I even reformatted the TB drive.

I'm convinced it's the TB drive. Yosemite was released on 16th Oct and all was fine UNTIL I got a TB drive one month later (14th Nov). This is when the trouble started.

Apple - please sort.

When your iMac won't wake up (i.e. black screen) ... is your TB drive light on? If it is, it's still seen as a "Startup Disk".

The light is off. My Mac is definitely sleeping as I can hear the fan

I realise from my last post, I've immediately blamed Mavericks but shouldn't have. When I get time, I'm hooking the TB disk to my MBP to see if it suffers the same issue as my Mac does.

I am having the same problem but not with a TB drive, but rather a USB drive. This has started to happen after an upgrade to Yosemite 10.10.2 beta. The thread is probably on the right track with the drives interfering with the wake up. I will be disconnecting the drive and see if the problem goes away and post my results.

May be the same issue. The problem went away as soon as I disconnected the drive. I have another TB drive connected, which wasn't a Time Machine drive, and no problems. I did the instructions per LaCie reconnected the problem drive, and haven't had the problem since.

I've switched off my 2Tb USB drive and a 3Gb firewire drive. Time machine (a 1Tb USB drive) and TB drive are on and connected. So far so good.

I'm not running the Beta

I hate to say it, but after working for 3 days, it failed to wake again!! I wish Apple would take this seriously. Why should an external drive hang a system!?!? Blaming someone else just to get out of correcting a serious problem leaves me feeling unimpressed. I try formatting the drive and partitioning it per the instructions. What is there to lose??

Same here. Seems pretty clear that it is a problem with Yosemite to me. I'll call Apple as soon as I get a free minute.