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Need help with EXT HD Static problem

S

Six118

macrumors newbie
Original poster
Aug 29, 2011
14
0
Afternoon all, for a little bit of background, Im a student, I've just bought an external HD enclosure in order to house an old 250gb HD to use with time machine on my 3 week old MBP 13. The HD is working fine, and is backing up perfectly. However, when its plugged into the power, and the usb cable is connected to the MBP (the instant it touch's the usb housing of the MBP) my external monitor disconnects and then roughly 5 seconds later reconnects to the MBR after which it starts to flicker extremely fast (almost beyond the point of perception, but still annoying.) Furthermore, the next time any sound is played on the system (after plugging in the HD) an extremely annoying humming sound starts playing, almost like I can here the HD spinning through the headphones?

Not really use what is causing the problem. My first thought was that there was simply some static built up, but i'm not receiving any shocks. Second though was that there may be a short circuit between the thunderbolt port and the USB, but no other usb device causes this problem.

Apologies for the long post, I hope it makes sense. Any help on this would be greatly appreciated.

Thanks
 
Exactly which part of the cable is making the contact that causes the short? What is it made of?
 
It is the metallic part of the usb cable that is going into the MPB from the external HD. As soon as the metal touch's the female usb socket on the MPB, the afore mentioned things happen. I dont know what type of metal its made off, presumably its aluminium, its certainly not gold.

I should mention that this is not a usb A-A connector. Its an A-B connector, the B connector being in the EXT HD.
 
Sounds like a grounding problem. Usually a hum like that is caused by a ground loop fault and is being picked up by the computer and transmitting over the speakers. Are you using the groused cord for the MBP (3 prong adapter) and a grounded connector for the HD? I would assume that the power supply for the HD isn't grounding properly from your description.
 
What exactly do you mean am I using a grounding cord for the MBP. The power cord into the wall has three prongs if thats what you mean? And how do I know if the HD connector is grounded? (it to has a three prong plug)

Thanks for the help guys
 
The third prong is the grounding prong; that's how you know. When you plug your HDD into the MBP, is it already "on?" If so try leaving it off, plugging it into the MBP then turning it on.

If that doesn't work, you should get a new cable.
 
Yes its off when I plug it in. Also, I've tried 4 separate cables with the same results :-(
 
You are using the grounded plug. The MBP ships with two connectors, a standard 2 prong connector (which doesn't have the capability to connect to earth ground, but is still fine as the MBP handles the grounding in another way) and the 3 prong connector which allows connecting to earth ground. With the other having a grounded plug as well, somewhere you are not grounding correctly and creating a ground loop. It could be something beyond your control and within the wiring of your house (or where ever you are using this HD and MBP).

If the issue is happening at different locations (say work and home) then I would suspect that the HD is not connected correctly or is faulty and not grounding sufficiently. What kind of HD external caddy is this (brand and model) as some of the cheaper made ones are the culprits with their subpar power supplies. With the shock occurring and the hum, it is definitely a grounding issue. Sometimes this can only be fixed with an electrical component such as a line conditioner or UPS that would remove your electronics from the ungrounded electrical loop of your source and place them into a controlled electrical loop (I once lived in an apartment that was so old this was my only remedy as the wiring needed entire replacement and the owner wouldn't pony up the cost).
 
It is not the best recommended method, but you could obtain a 3 prong to 2 prong adapter and use this between the power supply cable and the outlet. In extreme situations this is sometimes the recommended fix/ troubleshooting technique for testing extreme ground loop situations. It sounds like the item is defective and should be returned for replacement. I would contact the seller about an RMA.
 
Will do, thanks for all the advice guys. Just going to buy a proper external HD and send this housing back. Thanks again.
 
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