I can’t connect more than one USB de­vice

Mac Format - - APPLE TALK -

I’ve tried con­nect­ing a num­ber of de­vices to my Mac­Book Pro but have found if I try to connect two or more, us­ing ei­ther USB ports or a USB hub, the com­puter re­ports ‘disk not ejected prop­erly’. Some­times it fails to recog­nise the de­vice and re­moves it from the desk­top, or it stalls op­er­a­tion and I have to turn the com­puter off at the power but­ton.

I’ve tried eras­ing the hard drive and re­in­stalling the OS. I con­tacted Ap­ple Sup­port and they sug­gested a SMC and NVRAM re­set, and restart­ing in re­cov­ery mode. None of th­ese have helped. The com­puter has been to an Ap­ple dealer who tested the hard­ware but found noth­ing. Could a virus be present on the USB de­vices I’m try­ing to connect? Do­minic Oro­sun

This has noth­ing to do with viruses or your hard disk or OS X. It’s a hard­ware prob­lem. Some­thing is caus­ing the moth­er­board to lose the con­nec­tion to one of your de­vices. This can be caused by too much cur­rent draw on the USB bus. I’ve heard of cases where untick­ing the ‘put hard drive to sleep when pos­si­ble’ box in En­ergy Saver pref­er­ences helped, maybe be­cause it avoids the brief cur­rent surge on the USB bus when the drives need to spin back up again. But in most cases it’s sim­ply a mat­ter of re­plac­ing your USB ca­bles. Old or worn ca­bles can have a bro­ken wire with the ends loosely touch­ing, or a dry sol­der joint at the plug end. The con­nec­tion breaks and the Mac thinks the plug has been pulled. Some­times the bad con­nec­tion is on the de­vice and a Thun­der­bolt port may work in­stead, if avail­able. It prob­a­bly isn’t a loose con­nec­tion on the USB ports of your moth­er­board. You most likely only need to in­vest in new USB ca­bles.

Putting hard disks to sleep when pos­si­ble saves en­ergy, but this has been re­ported to cause prob­lems with USB de­vices on some Macs.

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