USB hub crashes on iMac after sleep

Hi, I'm new to macs and I am not sure how the usb ports work with powered usb hubs or how the sleep function works. My hub, a Dlink 7 port powered hub, has worked perfectly with my PC for a couple of years but now I have moved to the iMac it sometimes crashes after my iMac wakes up. Pulling the usb input into the hub from the mac and replacing it resets it.

The crash only seems to happen after the machine has been in a more prolonged sleep and doesn't always happen. However it happens at least once a day, sometimes more.

I would really like to understand what happens when the iMac goes to sleep. What happens to the USB port outputs? Do they turn off or reduce power?

iMac 2.8 i7 21.5 mid 2011 10.7.1
External firewire drive connected for Timemachine.
Plugged in to DUB H7 DLink powered hub: Wacom tablet (old), HP printer D1660, Canon scanner Lide 210, Logitech USB mouse. Only the hub is plugged into the iMac.

Various log files from the system can be read from the Console app (in Application\Utilities). I think the messages you are interested in would be in the system log file but I am not sure. The suspect entries will likely be time stamped at or near the time you attempted to wake the machine. Perhaps others can clarify that. Console logs are not always my best friend.

I had a similar problem some time ago and the exact cause did not appear in the Console logs. The problem could be the hub, as you suspect, or it could be one of the devices attached to the hub. One way to find out is to disconnect all devices from the hub and attempt to duplicate the problem. Gradually add devices back until the problem recurs. The last device added may be at least partially to blame.

In addition to what Slydude has suggested, take a good look at the Energy Saver settings in System Preferences. Take particular note of what is set for putting the hard disk to sleep. If checked, uncheck it, and see if that stops putting the hub into stasis as well.

Good catch hughvane I did not think of that as a possibility at all.

Thanks for the help

Because the problem is intermittent (it went 2 days without crashing this week and then crashed again after its first sleep) and because I cannot have some of peripherals switched off for long (i need my printer a lot e.g.) it may take a while to diagnose using your very logical suggestion slydude, but I will give it a go. I will also see if unchecking disc sleep helps although i would have thought the disc spinning was pretty important part of energy saving - but I'm only guessing.

i will certainly report back at some stage as it may help others.

In the meantime, if any one can point me to an article or resource that explains in detail what happens to the USB and firewire and Thunderbolt ports when the iMac I own goes to sleep, I would be very grateful. I have searched the web but can't get a definitive answer.

iMac 2.8 i7 21.5 mid 2011 10.7.1
External firewire 800 drive connected for Timemachine.
Plugged in to DUB H7 DLink powered hub: Wacom tablet (old), HP printer D1660, Canon scanner Lide 210, mighty mouse. Only the hub is plugged into the iMac.

Well, I never did get to the bottom of it. But a couple of weeks ago I replaced it with the belkin 7 port hub and it works perfectly. No crashes, and all the lights go off when the computer goes to sleep. I like having two of the ports on top as well, makes it easier for the occassional gadget and for memory sticks. And stupidly cheap. (less than £10.00 from Amazon).

I hope that helps with others looking for a hub for their Mac