power supply question

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Here is a simple question re the new power supplies that are currently
about that have a 24 pin split connector block. I was under the
impression that you could start any DDR 1 or 2 motherboard with one of
these. They have a 4 pin connector [black and yellow] as well as the
extra 4 pins keyed into the main connector block. I assumed that you
just slip this down and out of the way, plug the other 20 pin block
into an DDR1 ATX or MATX motherboard, plug in the 4 pin yellow black
connector and away it should go

I bought two of these psu's a couple of weeks ago and niether will
start any of the atx/matx boards here including the new board i bought
today [msi k8m800 with ddr1]
the board fires fine with an old style atx supply i use as a test

are both new supplies faulty or am i missing something here??

Re: power supply question

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I wouldn't assume anything with the hardware today. I've read from posters
that they bought a 20 + 4 pin PS and it wouldn't start their mb that
required a 24 pin connector. They went to another brand of PS that had a
solid 24 pin connector and it would work. I can easily believe it's the
other way around. What exactly is going on I don't know but one needs to be
cognizant that one PS will not fit all.

Jan Alter

Re: power supply question


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Yes, you can do that presuming it is a standard 24 pin
PSU... the extra 4 pins don't have any unique functionality,
they are only *redundant* (for extra current potential that
more modern system will, in theory, need someday) 3.3V, 5V,
12V, Ground.  I suppose if someone tried to, they could
deliberately put enough power hungry cards in a board's
slots to need the extra 4 pins, but typically the # of power
leads from the PSU aren't the problem when there is one,
it's the board's trace resistance.  For example the PSU may
be delivering 12.0V fine at the connectors but it's dropping
down to 11.8V across the board.

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Two what, exactly?  Makes, models, etc...
If they're generics, that's a pretty significant unknown
variable, they might be quite overrated.  There's also a
certain brand of PSU that's been deeply discounted recently
that had such horrible manufacturing & QC that it wouldn't
surprise me at all if 2 out of 2 were dead, but for various
reasons I'll refrain from mentioning the brand unless it's
what you have.

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Maybe their input voltage selection switch (110/220V) is set
wrong?  Otherwise, the PSU do seem suspect, does anything at
all happen when you try to start a system with one?  Do
their fans spin?  

How about if you hook the PSU up to just one hard drive,
_nothing_ else, then use a paperclip to short pin 16 (green
wire, PS_On pin on 24 pin PSU) to any ground (like pin 15 or
17, a black wired pin).  If you do that, the PSU should turn
on, fan spinning, hard drive on as well.  At that point if
you have a multimeter you might take voltage readings, but
expect the 3.3V rail and possibly 5VSB to be off a little
since they have no load from a HDD.

Sometimes I'll come across a board with some wierd startup
glitches, where the PSU can be connected initially and the
board (with necessary stuff in it, CPU/memory/video) seems
dead, but if the PSU is then unplugged (I generally wait a
dozen seconds or longer but sometimes it "might" even work
if replugged right away) and plugged back in, the
board/system starts up fine thereafter, it just takes one
attempt at power on and disconnect, rarely two or more,
before the board revives.  I'm not sure exactly why this
happens, at times it seems to be too much load on the 5VSB
rail but in other cases there was only a minimum load on
that rail.  Regardless, this was a board issue, not per PSU,
and happened with 20 pin PSU, too.

Older PSU often have more 5V current capability, is it
possible these new PSU don't have enough 5V current?  The
board you mention uses 12V rail to power CPU subcircuit, but
some other things that can tend to use more 5V current
include older generations of AGP video cards with external
connectors, multiple PCI video cards.

Re: power supply question

scully wrote:
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Maybe the fact that modern supplies are missing the -5V signal, is
upsetting your boards ? -5V should not really be needed, but there
have been cases where a board won't start without it. The only
way to detect a board that uses -5V for some reason, is to
Google on the board model number, and see if someone else has
already discovered the issue. Since you've tried a number of
different motherboard models, somehow that doesn't seem likely.

Otherwise, I see no reason for a 20+4 type of 24 pin power supply,
to have issues whether the extra section is joined or not. The extra
section is only really needed, for exceptional PCI Express loading
situations. An SLI or Crossfire setup would be a good reason to
use a full 24 pins for the job. With single video card, 20 pins should
be enough.

Make sure you are placing the right 2x2 part on the processor power
input. Two yellow wires and two black wires, is the ATX12V 2x2 connector
that powers the processor. The 20+4 slide-off section, should have
four different color wires on it, and should not be confused with the
one having two yellow and two black.

Would the power supply be a member of the Antec NeoHE family ?

Do the fans spin when you press the power button on the front of the
computer case ? Did you connect the computer case power switch cable to the
motherboard PANEL header ? An ATX supply won't run until the motherboard
sends the signal to start, and for that you need to use the power switch
that connects to the motherboard PANEL header.

There is a difference between "fans not running" and "fans running but
won't POST". The first case, means that PS_ON# is not being sent to
the PSU, to turn it on. The second case, means the PSU has started,
but some voltage must be missing. In the second case, when fans are
running, you can use a multimeter and probe the metal exposed on the
backside of the 20 pin connector, to see if all voltages are present
and accounted for. If "fans not running", then the only voltage you
expect to see is +5VSB. If +5VSB is not a full 5.0 volts, then perhaps
the motherboard is presenting too much load on +5VSB, for whatever
capability the PSU has..


Re: power supply question

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no its an auriga mpt 400

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no signs of life excpet a lit power led on the board

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tried shorting the pins and the switch

thanks for the detailed responses chaps

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