Help me not brick my KVM!
November 18, 2010 5:05 PM   Subscribe

Which polarity on an AC adapter is most common? or.. most likely to work for me?

I know polarity is important on AC adapters. That said, I have a KVM switch that I inherited, without its AC adapter. I know about typical polarity markings for AC adapters, but on this switch, there is no such marking, whatsoever. Just "DC 9V". I'm fully cognizant that I might only get one shot at this, and may break the KVM with the wrong polarity... That said -- Which one is more likely? Tip negative? or tip positive? An image of the KVM
posted by frwagon to Computers & Internet (7 answers total) 1 user marked this as a favorite
There are no other identifying features on the KVM, like manufacturer or product ID?
posted by zamboni at 5:07 PM on November 18, 2010

Best answer: Tip positive is far more common. I'd guess there's a 95% chance your KVM's jack is tip positive, and maybe a 10% chance you'll do any damage if it turns out to be tip negative and you disconnect it right away when it doesn't power up.
posted by contraption at 5:09 PM on November 18, 2010

Response by poster: It is, unfortunately, a very generic looking KVM. Beige steel case, only markings on it are identifiers for each of the pc's connected to it, a power switch, a CE electrical certification logo, and a tag indicating how to activate the scan mode.
posted by frwagon at 5:11 PM on November 18, 2010

Response by poster: Tip positive it is! Thank you contraption!
posted by frwagon at 5:18 PM on November 18, 2010

It's a risk, but a pretty safe one. Keep in mind that if it doesn't work with either polarity that might just mean it was broken before you even had it.
posted by contraption at 5:21 PM on November 18, 2010

Response by poster: It fired up perfectly with tip+.
posted by frwagon at 5:22 PM on November 18, 2010

It's quite easy to tell which is which if you open it up and look. The negative terminal will be connected to a ground plane which is usually a large run of soldier that goes all over the PCB. The positive goes only one place, right into a voltage regulator.
posted by Rhomboid at 5:39 PM on November 18, 2010 [1 favorite]

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