Chris' point is compounded by the fact that manufacturers try to cut every imaginable corner and don't properly overrate the voltage spec on their caps.
On Mon, Nov 7, 2011 at 10:22 PM, Chris Knadle <[email protected]>wrote: > On Monday, November 07, 2011 07:03:50 PM, Adam wrote: > ... > > The first time this happened was two weeks ago, and somehow after a > > few hours the problem, whatever it was, "fixed" itself. This past > > weekend I powered it down for the first time since then, and it did > > not power up at all. During that time, I used my DMM to measure one > > of the peripheral power connectors (the kind that would power a PATA > > drive), and discovered that when AC is applied, the +12V line rises > > within about half a second to about 0.67V and stays there. When AC > > is removed, that voltage gradually drops to zero as the LED flashing > > slows down. When the +12V line is steady at about 0.67V, the +5V > > line is steady at about 0.27V. > ... > > Obviously something is very wrong here. My question here is, is it > > more likely that the problem is the power supply or the > > motherboard? > > I'd say this is got to be a power supply problem. I've recently found out > some very interesting things about power supplies, which I'll share. [This > came up on the LIMARC "Tech Net" a few weeks ago, which had a power supply > expert on the radio that explained the follow details.] > > First, non-air capacitors have a limited lifetime. Here's where it gets > really interesting, though: a typical lifetime rating is around 2,000 > hours. > Yes, you read that right: in 24/7 use terms that's about three months. The > reason is that over time, non-air capacitors slowly break down such that > the > voltage rating slowly lowers. When the voltage rating finally lowers to > the > voltage that is in use, it arcs over and the capacitor becomes a dead > short. > > And that would explain your funny ticking sound as well as the voltages you > see; if an internal capacitor has become a dead short, the power supply > keeps > trying to start up and ends up being shunted. > > The better answer is to simply replace the power supply, assuming you can > find > a suitable replacement. But if you are really curious, you could take it > apart and try to measure the capacity of each of the capacitors to find out > which one of them went bad. > > -- Chris > > -- > Chris Knadle > [email protected] > _______________________________________________ > Mid-Hudson Valley Linux Users Group http://mhvlug.org > http://mhvlug.org/cgi-bin/mailman/listinfo/mhvlug > > Upcoming Meetings (6pm - 8pm) MHVLS Auditorium > Dec 7 - An Intro to Chef > Jan 4 - Recovering the Brownfield: Revitalizing Open Source Projects > Feb 1 - Home Networking Made Simple with Amahi Home Server >
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