John said:
Now posting from my secondary PC.
At first, naturally I thought the BIOS was broken. Symptoms seemed to
get worse over time and trials, down to the point that the CPU (fan)
was spinning up when the PS on/off switch was flipped on, and then it
went off, and then it repeated the same over and over again. Of course
the PC was stripped down to the bare essentials. Fired up my spare PC.
Moved the DVD drive into it, to see if a long standing problem with its
door not properely closing would occure. It closed just fine. Now I am
wondering if the problem could (coincidently) be the PS instead of the
mainboard. Wish I could test the older PS on the new MB, but it has
only an old 20 pin MB connector. I could test the newer PS on the old
MB, but not sure I want to risk it.
Anybody know if the same power suply output that powers the DVD drive
door also powers the CPU? Both 12v?
Thanks.
Do you have a multimeter you can test with ?
*******
Yes, it is possible the same rail powers both. An experienced power supply
person, can tell by looking at the innards. Sites like jonnyguru.com sometimes
delve into the details of individual designs. There is one other web site
that takes apart power supply for analysis purposes.
A single output rail can be connected to all 12V loads (pcpower.com approach).
A single output rail can have current limiter circuits inserted in each
12V output leg, to simulate independent outputs. I expect that is a common
design technique now, as it is cheaper to make and has most of the
desired safety features. It seems to be the design intent of the ATX 2.2 spec.
A power supply can have multiple, independent outputs. A giveaway is the
power supply chassis may be a lot longer than normal. If you look at the
average power supply today, they're back to "normal" size, which implies
a return to one monstrous output, plus some current limiters for protection
purposes. Some guys can tell you exactly how it works, by looking at the guts,
but I can't always pick apart the different types. "Larry", who posts here
regularly, knows them a lot better than I do.
*******
The main reason for wanting to plug a 24 pin main power connector
into any board, is for SLI or Crossfire video card configurations.
(And SLI or Crossfire implies a PCI Express motherboard.)
The motherboard 12V rail may be heavily enough loaded there, to want
the second yellow wire a 24 pin connector gives you.
For single video card or no video card applications, a 20 pin connector
can be used on a 24 pin motherboard. And even the vice-versa case is allowed,
you can plug a 24 pin into a 20 pin, as long as you can figure out the pinout.
A lot of 24 pin connectors, can be split into two pieces, at the hinge between
the two sections. For those supplies that don't hinge, as long as there aren't
tall components in the way, you can plug a 24 pin into a 20 pin motherboard.
This picture, is of a 24 pin, plugged into a 20 pin motherboard. As long as
there is no electrolytic cap right next to the 20 pin, to bump into the four
"overhang" pins, it will fit.
http://www.playtool.com/pages/psuconnectors/24in20.jpg
This picture is a 20 pin power supply and a 24 pin motherboard, valid
as long as there is just one PCI Express video card installed (rough rule of thumb).
http://www.playtool.com/pages/psuconnectors/20in24.jpg
In neither case, is an adapter cable required. An adapter cable doesn't solve
any electrical problems. An adapter cable is good if you need additional cable
length, and the harness on the power supply happens to be too short.
So most of the motherboard requirements are met just fine, with the lowly 20 pin
connector.
*******
If you need specs, this is my spec list. But this doesn't describe in detail,
how the power supply company must design what is inside. They have a lot of
flexibility in what they can do. And what is printed on the spec label, isn't
guaranteed to elucidate the architecture inside. (When it says "12V1" and
"12V2", they could both be coming from the same output side thing.)
http://web.archive.org/web/20030424...org/developer/specs/atx/ATX_ATX12V_PS_1_1.pdf
http://www.formfactors.org/developer/specs/atx/ATX12V_1_3dg.pdf
http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf
Paul
