[ut2004] still no love with ut2004 amd64

Douglas Wade Needham cinnion at ka8zrt.com
Sat Nov 5 08:52:34 EST 2005

Joel has the right of it.  I have a 1KW power supply in a computer
here, but it won't work in my ATX system. ;)  Seriously, the specs on
the side of the power supply are the critical detail here.  If your's
says that it cannot deliver more than X amps on the 5V rail, and no
more than Y amps when combined with the 3.3V rail, then you must make
sure that this limit is not being exceeded AT ANY TIME.  Because of
this, you may have to make some phone calls or do some guessing for
things like your mobo and graphics card (the morons who produce the
docs for them should be shot for not putting in power specs), and you
will also likely have to do some reading through docs on the CPU and
drives.  But the end result is that you should be able to add up all
the max values for current on their respective rails and find that you
do not exceed 90% (a typical engineering margin) of the ratings on the
power supply, including the combined rail limits.

Also, check your voltages via the bios system health.  Or better yet,
if you know someone with a very strong electronics background and the
right equipment, measure them at the connector ***UNDER LOAD***.  The
specs for ATX 2.01 are pretty tight (+/-5% for all but the 3.3V rail,
which is +/-4%) and if you have an oscope, you should ideally see
almost no ripple, and what you do see should not take you anywhere
near the limits.

Also, while it has been a problem for a couple of years now, not
everyone has fessed up to using what have turned out to be defective
capacitors.  For those of you who are not familiar with this, here are
some details.  Trying to come to market cheaper, manufacturers started
buying cheaper caps, and the cap manufacturers saw this and tried to
lower their costs.  A few of these cap manufacturers apparently stole
some designs, but got a incomplete formula for the electrolyte (think
goo) which goes into those little can capacitors which are all over
your mobo, graphics card, etc. and throughout your power supply.  It
turns out that the electrolyte is unstable and will break down with
usage, which produces a pressure inside which shows up as either a
deformed or leaky cap.  For more info on this, read:


But the end result of these bad caps can be things like bad voltages
at the CPU (which almost never directly uses the voltages from the PS,
but which instead has its own voltage regulators), and you can see
wierd behaviour.  Worse, you can eventually reach a point where they
will fail, and you can damage just about everything in your system
when this happens, including your hard drives, even if it is one of
the ones by your CPU which fails.  So I would also say that a very
good brand (name recognition is not enough) is necessary.  Read
reviews on the power supplies, talk to friends, and if possible, make
friends with the techies at a good computer parts wholesaler and get
the info on any power supply before you buy it.

- Doug

Quoting Joel Wiramu Pauling (aenertia at aenertia.net):
> On Sat, 2005-11-05 at 09:11 +1100, Dean Hamstead wrote:
> > i have a 400w power supply, with a mboard and two hard disks
> > running off it.
> wattage means nothing.. Check on the side of the PSU and look for
> 5V/<some amps> 12v/<some amps>
> Your 12 volt rail should ideally have 24+ for an amd64 chip with a
> fairly decent graphics card.

Douglas Wade Needham - KA8ZRT        UN*X Consultant & UW/BSD kernel programmer
Email:  cinnion @ ka8zrt . com       http://cinnion.ka8zrt.com
Disclaimer: My opinions are my own.  Since I don't want them, why
            should my employer, or anybody else for that matter! 

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