SATA Port Looped Back Go Boom ?

Posted on 2013-05-22
Last Modified: 2016-11-23
I have a client who recently had a workstation failure. It's a Dell 390 Precision that is used to store and view medical images. The system has two internal SATA drives, and also connects to an external NAS.

They took the system to one of the few remaining big computer store chains to evaluate. The store said they tried a power supply, but it did not help the problem. Now I have been asked to look the system over and help the client locate and purchase identical hardware to migrate the drives into. Ok fine we can do that.

When I opened the system up, I noticed that one of the SATA drives was no longer connected, but I could not find a loose connector anyway. Then I realized that one SATA port had been looped back into another SATA port. (see photo) Does anyone have any experience with what happens if you do that ? I also noticed that there were 4 of the larger capacitors with that telltale failure bulge. I'm just wondering if this scenario is in any way possible:

- System comes in with a bad power supply
- While swapping the supply and plugging/unplugging cables, a loose SATA cable is looped back to the controller instead of going to a drive
- Motheboard blows.

Perhaps looping back the port does nothing. I've just never done it or heard of it being done. Thank you !!!!
Question by:montygary
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LVL 47

Assisted Solution

dlethe earned 166 total points
ID: 39189444
yes, it is possible. BTW Stay away from that chain.  A professional would have a power supply tester and a motherboard tester and would not have to leave things to guesswork.

Who are those bozos??

Author Comment

ID: 39189474
They were (since January) TigerDirect. I do avoid them (repair-wise anyway), a customer took the system in. Can you elaborate ? Have you seen this or know of cases where it has occurred ?
LVL 47

Expert Comment

ID: 39189527
Look, any time somebody cracks open a case there is risk of static or stored electricity blowing anything.  A bad PSU can fry a motherboard or carry a charge that destroys a SATA port and lets the rest of the motherboard survive.

A person who is so inept that they can't identify both ends of a 12-18" long cable is more than capable of doing damage.   A screw could have been loose all along and transporting it in the car could have jarred it.  The cable could have been forced. It could have been a stranded cable and a small copper fiber on the inside shorted the 2 power pins or resistance was so high that it drew extra current resulting in higher amperage load and component failure.  

Your question is whether or not this is possible.  I've seen all of the above at one time or another, and so much more.  Yes all of these scenarios are possible.  

If you are asking because you want to point a finger, then pay a testing house with proper equipment to do a forensic analysis.  But that might cost you $5K or more, and you have no guarantee that they can prove beyond reasonable doubt root cause.
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Author Comment

ID: 39189577
I can conjure up a good story as well. I'm looking for someone who has had, seen, or heard about the experience of looping back a SATA cable. Or the specific circuit experience to say "here is what will happen". But thanks.
LVL 47

Expert Comment

ID: 39189608
If the cables, plugs, and receptacles are all perfect, and the user did not try to force anything, including push/pull and bend the motherboard enough to cause anything to create a tiny break in the copper, then no damage can possibly occur.  Same is true with both power & data cables.

If you look at the pin-outs, the reason is obvious.  All voltage/ground connections are in parallel and are already connected together.  As you only have one signal line then there is no potential across them.

But you can not know for sure unless you get a magnifying glass and visually inspect the board to look for damage and use a high impedance multimeter or preferably an oscilloscope to know with 100% confidence that there is no damage from a brief closed circuit.

in summary, unless the person mishandled the cable, or used a bad one, it wouldn't have hurt anything.
LVL 32

Assisted Solution

_ earned 167 total points
ID: 39189629
I'm with dlethe, thought it might be fun to risk an old mobo and try it.   ; D

Another point, since the system had already failed before they took it in, TD looping the SATA (assuming they did) is probably moot, since the caps were probably why it failed in the first place.
LVL 92

Accepted Solution

nobus earned 167 total points
ID: 39190019
i agree  the loopback does not hurt - or does any good either
probably a person did not not want any loose cables in the cabinet -and "fixed" it this way..

about the capacitors, - if you want to replace them - replace them all, not only the bulged ones
LVL 32

Expert Comment

ID: 39227128
Thank you much.     : )

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