Computer Hardware Talk Computer Hardware Talk    FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  polarity of the power supply for seagate st90000u2 hard-driv          Computer Hardware Talk Forum Index -> Computer Hardware Talk View previous topic :: View next topic   Author Message michalchik@aol.com Guest Posted: Tue Jul 15, 2008 1:38 am    Post subject: polarity of the power supply for seagate st90000u2 hard-driv Hi, A friend gave my sister a used hard-drive without the power supply. The case says the voltage, millamperage, and the fact it is dc but fails to say whether it is center positive or center negative. I have looked pretty hard on the internet and not found the info yet. Any suggestions? Thanks, Michael Back to top   Ads Advertising Sponsor UCLAN Guest Posted: Tue Jul 15, 2008 9:12 am    Post subject: Re: polarity of the power supply for seagate st90000u2 hard- michalchik@aol.com wrote: Quote: A friend gave my sister a used hard-drive without the power supply. The case says the voltage, millamperage, and the fact it is dc but fails to say whether it is center positive or center negative. I have looked pretty hard on the internet and not found the info yet. Any suggestions? Methinks you're not looking closely enough. Look right at the area of the power jack of the device. It's there somewhere. Back to top   Ads Advertising Sponsor kony Guest Posted: Tue Jul 15, 2008 9:37 am    Post subject: Re: polarity of the power supply for seagate st90000u2 hard- On Mon, 14 Jul 2008 18:38:51 -0700 (PDT), "michalchik@aol.com" <michalchik@aol.com> wrote: Quote: Hi, A friend gave my sister a used hard-drive without the power supply. The case says the voltage, millamperage, and the fact it is dc but fails to say whether it is center positive or center negative. I have looked pretty hard on the internet and not found the info yet. Any suggestions? Thanks, Michael 99% of the time the center is positive on consumer electronics. That's what you'd try first if you had to gamble, but if you open the unit and inspect the PCB you may be able to trace which jack contacts go to which traces or ground plane. A multimeter set to continuity or resistance mode would also indicate which is common to ground you'd find elsewhere on the board or the ground lead for the hard drive connector. Also, you didn't tell us what make and model so even someone who might have the exact same thing can't be sure if what they have applies to yours... since 99% is not 100%, we wouldn't want to tell 100 people and have one suffer the loss of it being reversed from the normal polarity. Keep in mind that this drive (enclosure?!) may require a regulated power supply, usually a switching type for lower cost and heat, not the unregulated ones which are also quite common in the voltage it probably uses (12V or 5V). Back to top   Ads Advertising Sponsor larry moe 'n curly Guest Posted: Thu Jul 17, 2008 7:50 am    Post subject: Re: polarity of the power supply for seagate st90000u2 hard- michalchik@aol.com wrote: Quote: A friend gave my sister a used hard-drive without the power supply. The case says the voltage, millamperage, and the fact it is dc but fails to say whether it is center positive or center negative. Is there a funny symbol next to the connector, like a dot surrounded by the latter C, something like this (dot not shown due to ASCII limitations)? - -------C------- + The line on the right goes to the dot in the center, which indicates the center contact, and the C represents the surrounding hole. In the above example, the outer contact is negative, the inner one positive, which is the most common connection. If you have a multimeter (even a $3-5 digital one is fine, but avoid cheap analog meters), you can measure the ohms between the case and each contact, and the contact that shows the lowest resistance is the negative one. Measure both ways, one way with the black meter lead touching the case and the red one the power contact, then reverse the leads. If the case is plastic, measure between the contact and the outer metal shell of the USB or firewire connector Can you open up the drive case? It may be held together by screws hidden under the rubber feet, or it may have snaps that can be pressed where the two halves meet. The negative connection of the power socket should be attached, either directly or maybe with a black wire, to a copper trace on the circuit board that goes to the negative lead of a large filter capacitor, which will be a plastic-sleeved cylinder with minus signs printed on one side. Also the outer shell of the USB or firewire connector will be attached to the same copper area. 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