On Tuesday, November 08, 2011 11:40:51 AM, Allen Weiner wrote: > On Mon, 2011-11-07 at 22:22 -0500, Chris Knadle 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. > > The problem with Adam's PC may indeed be the PSU. But regarding the > lifetime of capacitors, here is a contrary view on PSU life from some > non-experts on the Anandtech Power-supplies forum: > > It is from the recent thread "How long does a PS actually last?" > http://forums.anandtech.com/showthread.php?t=2201228 > > Here is one comment from that thread: "I've seen computers from 1990 > still running fine. That would be a 20 year old power supply." There are > other similar comments on that thread. > > I own two year 2000 Dell PC's each of which has seen over five years of > 8-10 hours per day, 6-7 days per week of use with no problems.
Hold on -- I didn't say /anything/ about how long a /power supply/ will last. What I /said/ was concerning /stated rating/ of the longevity of /capacitors/. I'm very well aware that power supplies can operate for decades. What I'm pointing out here is that there's something /confusing/ and contradictory going on concerning the MTBF rating of [ceramic|electrolytic|tantalum|oil- filled|etc] capacitors verses how long the items those capacitors are /in/ are in use for, and something new I've discovered concerning the failure [mode| mechanism] that those capacitors have. -- 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
