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iMac won't restart with USB hub plugged in  



I have a 2013 iMac running 10.4.1. I've had an Anker powered USB hub in for years. Noticed recently that the iMac will hang on a black screen on restarts until i unplug the hub.

I tried a pram reset and basic maintenance in Cocktail. 

Could the hub be defective now? if so, any recommendations for a new one?




2 Answers

What happens if you attach it after reaching the desktop? Does it work then? Can the machine boot in safe mode with it attached?

Try to reproduce the issue with the USB hub connected with nothing connected to it and nothing but the hub connected to the Mac. If the issue persists, try another USB port on the Mac and try again.

You need to isolate if the issue is related to a USB port on the Mac or a device attached to the USB hub,

So the idea here is to simplify the hardware configuration until you isolate the problem.

So again,

  1. Only hub connected to the Mac.
  2. Nothing connected to hub.
  3. Start up Mac.
  4. Issue Resolved?
  5. If so, connect ONE device to the hub and try to reproduce the issue. Attach devices to the hub one by one, restarting as you go along until you spot the device affecting startup.
  6. When you find the affected device consider if a driver or something else might be missing or a power supply issue for the device or a potentially bad USB cable.

Of course, suspect the USB cable as much as you suspect the Mac USB port.

You can use system report to test the USB ports on the Mac, attach a device to each USB port and rescan the ports to confirm if the USB ports are working as expected. Start here actually. Make sure the USB ports on the Mac work before anything else.


You need to do some troubleshooting before assuming it's the USB hub. It could be the hub but it also could be a cable or one of the devices connected to the current USB hub. Remove all devices from the Hub and startup with the hub only, if it successfully boots then it's likely one of your devices. You will need to add each one by one until the problem comes back.