Mac not recognizing external drive for time machine

[srlanza]

I've used a western digital external drive w/time machine since I bought my 2009 iMac. Last week the Mac stopped recognizing the drive so backups weren't being made. I thought it was a problem w/the external drive so I bought a Seagate Backup Plus for Mac. It set up perfectly and began making backups with time machine.
Now my mac only recognizes the seagate external drive occasionally; so time machine isn't always backing up. I keep rechecking time machine settings; sometimes it shows no external drive for backup, sometimes it shows the seagate drive.
At this point I starting to think the problem is my Mac, since this is happening w/the new drive as well.
I'm running Yosemite 10.10. Are there any other settings/preferences that could be causing this other than the time machine preferences? Or has my Mac finally bit the dust?

Thank you!

 

[johnodd4]

it could be a bad capacitor in the iMac there is a capacitor that controls voltage to the usb ports when the capacitor starts to go hard drives and other devices stop working check other devices usb thumb sticks and cell phones iPads iPhones and see if they work

 

[vansmith]

Have you tried different USB ports? It's very possible that the port itself is flaky (which is not indicative of a dying machine). You don't happen to be using the same cable either do you?

 

[srlanza]

I'm not using the same cables. I did check the USB port when I had the problem w/the western digital drive and the port was fine. I've just changed it w/the seagate but I won't know right away whether or not that's the problem; the mac & time machine are currently recognizing the drive. I'll have to wait to see if the seagate drive disappears on this port.
USB ports tend to be kind of finicky. Is there anything that can be done if one seems out of whack?
Thanks very much for your reply. Fingers crossed it will work this time.

 

[johnodd4]

there is actually you can use a powered usb hub and try that if you are not getting enough power to the usb ports the powered hub will work as a bridge once connected if your drives come online it was a usb problem

 

[johnodd4]

Have you tried different USB ports? It's very possible that the port itself is flaky (which is not indicative of a dying machine). You don't happen to be using the same cable either do you?

True and the reason i mentioned the capacitor is the same thing it gets flaky over time and works then doesn't the bridge trick usually works as well just depends

 

[srlanza]

Right now it's working in a different USB port, but that's a wait and see. I had tried switching ports w/the old western digital drive and sometimes it worked and sometimes it didn't. Hopefully this will do the trick for the seagate drive.
I have a powered usb hub; it's a tripp lite. But I thought you couldn't plug anything into it that used a lot of power, such as an external drive. I wasn't able to charge my ipad w/a hub and was told the ipad drew too much power.
I have 4 usb ports on my mac used as follows: external drive, powered hub, UPS, and router/modem. Are there more powerful hubs that work w/peripherals that draw a lot of power? The tripp lite does plug into a wall socket so my understanding is that's what a powered hub is.
Don't know what a capacitor is or what it does or how to check it.

Thanks.