Date: Wed, 29 Jan 2003 18:46:29 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Peter Wemm <peter@wemm.org> Cc: Dale Woolridge <dale-list-freebsd-smp-2@woolridge.org>, freebsd-smp@FreeBSD.ORG Subject: Re: Over heating of the ABit BP6 motherboard Message-ID: <200301300246.h0U2kTbJ084870@apollo.backplane.com> References: <20030130022752.1872F2A89E@canning.wemm.org>
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:The voltage spikes are the kicker, aren't they? In my research for the
:dead Apple Airport problem (caps swelling up), somebody reported that the
:spikes he was seeing were way above the nominal rating of the capacitor.
:Although the input is 12V, and the caps were rated at 16V, he ended up using
:25V caps because of the spikes. I did the same on mine.
:
:I suspect I have the same problem on my 8 port switches at home. Two of
:the three have now had an exploded electrolytic capacitor and subsequently
:shorted out the external power wall transformer and killed it. Collecting
:up the bits of the capacitor and replacing it solved the problem, but
:I'm not sure if I want to keep losing the power supplies.
:
:Cheers,
:-Peter
:--
:Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com
:"All of this is for nothing if we don't go to the stars" - JMS/B5
It's most likely that the capacitors are simply being made from
substandard materials with higher internal resistances. Sometimes you
can get around that by specifying HF (high frequency) caps. Voltage
spikes above the capacitor's rating (or even just near the capacitor's
rating) tend to blow holes in the gap material, greatly reducing their
life span, but won't necessarily make them melt down. e.g. a capacitor
spec'd at the voltage it runs at might last 20 years. A capacitor
spec'd at twice the voltage it runs at might last 40 years. Anything
that blows out in less then 10 years is more likely to be
workmanship/materials problem (unless it is consistently overvoltaged).
The electrolyte dries out too quickly and/or inherently high internal
resistances cause overheating in high frequency applications (such as
switching power supplies). The manufacturer might have put in non-HF
caps when he should have put in HF caps, etc. The sad thing is that
most brick makers don't care. If the brick lasts 5 years they are
happy campers.
This is why a 20 year old T.V. might still work while a 10 year old
computer might not. My old Amiga still works but I've had plenty of
computers bought since then fail for all sorts of reasons. Substandard
materials. Ah well.
-Matt
Matthew Dillon
<dillon@backplane.com>
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