new system bootup woes


A

Adam

Host OS: Ubuntu Desktop 12.04 LTS
Motherboard: ASUS Sabertooth 990FX AM3+ AMD SATA 6Gb/s USB 3.0 ATX
Computer Case: Antec Three Hundred ATX Mid Tower
Power Supply: OCZ ModXStream Pro 600W Modular


I am having trouble with power to brand new system.

After talking with OCZ tech support and doing a simple test,
we were able to get the PS fan to spin-up. OCZ Tech support concludes that
this is a strong indication that the PS is functional.

Next, I suspect that the Antec case's I/O panel wiring to mobo pins may
be the culprit. The wiring seems fine to me but still no power.
Maybe a loose connection? How to make a stronger connection?

Any ideas?
 
J

Jonathan N. Little

Adam said:
Host OS: Ubuntu Desktop 12.04 LTS
Motherboard: ASUS Sabertooth 990FX AM3+ AMD SATA 6Gb/s USB 3.0 ATX
Computer Case: Antec Three Hundred ATX Mid Tower
Power Supply: OCZ ModXStream Pro 600W Modular


I am having trouble with power to brand new system.

After talking with OCZ tech support and doing a simple test,
we were able to get the PS fan to spin-up. OCZ Tech support concludes that
this is a strong indication that the PS is functional.

Next, I suspect that the Antec case's I/O panel wiring to mobo pins may
be the culprit. The wiring seems fine to me but still no power.
Maybe a loose connection? How to make a stronger connection?

If the system powers up to where the power supply fan runs then start
looking a the motherboard. Any post codes? Indicator lights on
motherboard? Reseat RAM. Check CPU, remove all cards except video (if
not using onboard) and see if it posts then.
 
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M

mike

If the system powers up to where the power supply fan runs then start
looking a the motherboard. Any post codes? Indicator lights on
motherboard? Reseat RAM. Check CPU, remove all cards except video (if
not using onboard) and see if it posts then.
What does your voltmeter say?
 
A

Adam

mike said:
What does your voltmeter say?
Oh boy, that's new to me. I'll see if I can find any "how to" links on
troubleshooting with a voltmeter.
 
V

VanguardLH

Adam said:
Host OS: Ubuntu Desktop 12.04 LTS
Motherboard: ASUS Sabertooth 990FX AM3+ AMD SATA 6Gb/s USB 3.0 ATX
Computer Case: Antec Three Hundred ATX Mid Tower
Power Supply: OCZ ModXStream Pro 600W Modular

I am having trouble with power to brand new system.
Oh, that "trouble" since there can only be one. It's a secret trouble.

Doesn't sound like an OS problem since the unidentified "trouble" is
probably to get it powered on which is before the OS is even loaded by
the BIOS.
After talking with OCZ tech support and doing a simple test,
we were able to get the PS fan to spin-up. OCZ Tech support concludes that
this is a strong indication that the PS is functional.
Not really. PSUs that have crapped out by not being able to handle the
load can still spin their own fan(s).

Did you notice if the CPU's fan is spinning, too?

If using a mechanical HDD, do you hear it spin up on power on? How many
HDDs are connected? Tried with just one?

Did you populate all mobo RAM slots with matched memory modules? Or did
you mix them? They have a warning on their spec page saying "AMD 100
series CPUs support up to DDR3 1066MHz. With ASUS design, this
motherboard can support up to DDR3 1333MHz."

Did you disconnect all USB devices and then retest that the "trouble"
went away?
Next, I suspect that the Antec case's I/O panel wiring to mobo pins may
be the culprit. The wiring seems fine to me but still no power.
Maybe a loose connection? How to make a stronger connection?
Do you have a separate daughtercard for the video? Or are you using
onboard video? If a daughtercard, did you remember to hook up the PSU
4-pin connector to the video card's extra power connector?

The mobo has a 24-pin power connector. The PSU may come with a 20+4
connector: 20 pins in one connector with an ancilliary 4-pin connector
you add (slide on or rotate and snap into place). Did you use 24 pins
from the PSU to the 24-pin power connector on the mobo? Did you connect
an 8-pin connector from the PSU to the 8-pin power connector on the
mobo? The manual says "Do not forget to connect the 4-pin/8-pin EATX12
V power plug; otherwise, the system will not boot."

With modular PSUs, sometimes users hook up only the minimal connects and
omit some crucial ones.

Do you have 2 high-end PCI-e x16 video cards? If so, Asus recommends a
1000W PSU.
 
P

Paul

Adam said:
Oh boy, that's new to me. I'll see if I can find any "how to" links on
troubleshooting with a voltmeter.
Now you understand why I "bench test" on the kitchen table first,
before putting the system in the computer case.

You don't absolutely need *any* wiring to the front panel at all,
for a bench test. But what I do instead, is keep a push button switch
with two connector pins on the end, which slide over the PWR and Ground
pin pair. That's for turning the system on. I can also slip a screwdriver
tip between those two pins, to bridge them and start the system. That
requires a good deal of care and dexterity, and is only
practical when the motherboard is sitting on the kitchen table.

http://i61.tinypic.com/28bgwf9.gif

On the picture there, you can see that header has a "dangerous pair"
in the SPKR pin area. Don't bridge that +5V pin if you can possibly
manage it, to any adjacent Ground pins. It's another one of those
situations where there may be no protective fuse in the path.

*******

In the past, some Antecs have had wiring errors in USB or Firewire
cables (that's a 2x5 on the motherboard end, leading to a front
panel mounted connector). So I would not hook up the front panel I/O
wiring at all. On a couple Antec cases here (I have at least three
of them), I use the multimeter, set to ohms range, to verify the cable
wiring is correct. It's just easier to *not* use Antec front wiring, than
be bothered to do that. None of my Antec front USB ports are hooked up,
for this reason. I'm too lazy to correct the errors by moving the
pins around in the 2x5 end.

*******

I take it, OCZ had you do the "unconnected supply" test ?

For that one, you bridge PS_ON# to GND on the ATX cable.

Bringing the logic level low on PS_ON# is what makes
the supply fan spin, and the main supply section to function.
On page 37 here, that would be the green PS_ON# wire, to an
adjacent black GND wire. Some people recommend connecting
a dummy load to the supply, in the form of an old (scratch)
hard drive or something that draws a similar small amount
of power.

http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf

*******

This is a simplified model of the ATX supply. There are two
power generation circuits, and +5VSB is separate from the rest.

AC Input ------+--- +5VSB circuit
|
+--- +3.3/5.0/12V main section

When you switch the supply on at the back, the +5VSB starts to
produce power immediately. The fan will not be spinning at
this point. The +5VSB provides 2 to 3 amps max, and is
used as a supervisory voltage, amongst other uses. The
ATX power supply is convection cooled at this point, when
removing heat from the +5VSB circuit. Due to the modest
capacity of the +5VSB, it doesn't get too warm.

When the ATX power supply main cable has PS_ON# and GND
brought together, that grounds the pullup resistor on
PS_ON#. Normally, with a voltmeter, you'd see 5 volts
level on PS_ON#, and it's when that level is grounded
that the supply runs. The fan begins to spin, and the
main voltages begin to be produced. The motherboard
would be starting to POST at this point. The case
fans would be spinning.

If you attempt to start an ATX supply, and you see
the PSU fan "twitch" about a half inch of rotation,
that means the supply tried to start, but encountered
a serious short circuit (current overload) on the outputs.
To protect against burning any cables, the ATX supply
has latched off. Normally, you'd need to switch off at
the back, wait 30 seconds, switch on again, to make
another attempt to start the system. The reason the
supply "twitches", is the overcurrent is disabled
for the first 35 milliseconds, until the PSU has had
a chance to charge the output capacitors, and that
allows the fans to receive current for 35 milliseconds.
The fan blades can only "twitch" in such a short time
frame. If the "serious short" is present, when the
overcurrent detection is enabled at 35 milliseconds,
the power supply immediately shuts off the main section.

(The reason you wait 30 seconds, is to give any inrush
limiter time to cool off.)

In this diagram, the +5VSB is used to power the control
circuits. The motherboard logic "latches" the momentary
logic low level from the front panel switch, and drives
out a "steady" 0.0V level on PSON#. And that's what is
used to control the ATX supply.

+5VSB (0.0V level +5VSB
| means "run please") |
Pullup \_ Pullup
Resistor \ Resistor
| PS_ON# |
PWR X----+---- Motherboard ---- Open -------------------+- ... control
/ logic Collector (to of main
| GND X----+ Driver ATX + PSU
| | supply) | section
(Front GND GND
Panel
Switch - normally open, momentarily close to operate)

By removing any USB panel header or Firewire panel header wiring
from the front panel to the motherboard, you're removing
a possible place for electrical shorts to happen. Wiring
up the PWR button from the front of the case (two wire twisted
pair labeled PWR and GND), gives you enough control to turn
the system on and off.

*******

On an Asus motherboard, there is a green LED which is wired
in such a way as to monitor for +5VSB. If the ATX PSU is supplying
+5VSB, and the main PSU cable is wired up, the green LED should
be glowing. And the LED should not flicker. It should be
a solid level for the entire time that the switch on the
back of the ATX supply is in the ON position. Asus provides
the LED, to tell you when it is safe to work inside the PC.
The LED must be completely extinguished, before you
work on RAM DIMMs or pull PCI Express cards, that
sort of thing. It takes up to 30 seconds for +5VSB to
drain, after the ATX PSU is switched off.

Paul
 
L

larrymoencurly

Host OS: Ubuntu Desktop 12.04 LTS
Motherboard: ASUS Sabertooth 990FX AM3+ AMD SATA 6Gb/s USB 3.0 ATX
Computer Case: Antec Three Hundred ATX Mid Tower
Power Supply: OCZ ModXStream Pro 600W Modular
I am having trouble with power to brand new system.

After talking with OCZ tech support and doing a simple test,
we were able to get the PS fan to spin-up. OCZ Tech support concludes that
this is a strong indication that the PS is functional.
OCZ tech support is full of it because the only thing a spinning
fan indicates for sure is that the +12V rail is putting out at
least 5V to 6V, the minimum voltage that most 12V fans need to
spin up. It's possible one of the other positive voltage rails
isn't putting out anything, and you typically need all 4 positive
voltage rails working right for the computer to run, especially
the +5Vstandby line, which is separate from the main +5V. A cheap
digital multimeter is great for diagnosing PSU problems and a lot
of other things, unlike a PSU tester (the ones without digital
readouts but just LEDs are useless). Can you borrow a power supply?

Over the past couple of years, I've seen several brand new power
supplies not work with motherboards until I plugged and unplugged
their connectors several times, maybe due to oxidation or a coating
on the contacts so try this, 5-10 times.

Have you tried turning on the motherboard directly through the 2
power-on header pins on the motherboard? Do this with the front
panel cables disconnected. If that works, then you know something
is wrong with the cable wiring.

See that the memory and any plug-in cards are seated correctly in
their sockets. Also test with just one memory DIMM installed
(generally it's better to first test a system with just enough
hardware installed to let you see something on the screen -- makes
it easier to pinpoint the bad hardware).

Do your DIMMs have tall heatsinks that may be pressing against the
CPU's heatsink? That can prevent computer operation. Another
thing to check is the CPU heatsink because if it's not making firm
contact, the motherboard will probably turn off, but usually it
will start for a second. Sometimes 1 of the 4 CPU heatsink mounting
screws or pins is loose. And some heatsinks have terrible mounting
hardware on the bottom of the motherboard that can make it easy
to create a short.

Sometimes the motherboard shorts to the case, usually at one of
the mounting holes, a poorly supported corner, or where there's
an extra brass mounting post underneath that doesn't line up with
any of the holes in the motherboard. A brass post like that can
short out traces or even crush tiny surface mount components and
ruin the motherboard.

What kind of anti-static precautions did you take? Did you do
anything foolish, like wear shoes, socks, or long sleeves?
 
P

Paul

VanguardLH said:
Do you have 2 high-end PCI-e x16 video cards? If so, Asus recommends a
1000W PSU.
When debugging a power problem, at system startup
the components don't draw "max power". Even a modest
power supply, mistakenly connected to a high power system load,
should get you to the BIOS screen.

Whereas at one time, video cards had high idle current draw,
they've improved a lot. And even a gamer card can run cool
when it is idle. If you're using older high end video cards,
their power can be a bit obnoxious at idle.

*******

Startup condition (T=0, BIOS screen time etc...) :

Video card - min power, low clock, 10W each on modern cards
Processor - likely to be using one core
Disk drive - spin-up current of 12V @ 3A for first ten seconds

*******

Booted and idle in desktop (maybe 150W max system-wide):

Video card - min power, low clock, 10W each on modern cards
Processor - likely to be using approximately one core (12V @ 1.1A typ)
Disk drive - motor current stable at 12V @ 0.6A or less

*******

Booted and playing 3D game, tainted driver, SLI or Crossfire enabled:

Video card - 3D clock rate, gaming power level (200W, high end card)
Processor - likely to be using multiple cores (draws estimated TDP power)
Disk drive - motor current stable at 12V @ 0.6A or less

If the computer was unstable when 3D gaming, that might be
a sign the supply size is not correct for the load.

Asus offers a PSU calculator, but the numbers are too high.
For example, a system with no video card, was rated "350W".

http://www.service.asus.com/#!psu-calculator/c1ig3

This one was a bit crazy at one time, but they've refined this
since then. At one time, some DIMMs were rated at 25W each,
whereas you can use Kingston datasheets to get 2-3W estimates
for each. So when they say "most trusted", I really
prefer the sites to display their estimate for each
component for all to see.

http://extreme.outervision.com/psucalculatorlite.jsp

The "most trusted" power estimator, was shut down years ago.
A shame really. It listed the power number it used for
each component, so you could judge for yourself how
realistic the estimate would be. For example, it would
say my video card was 35W, and if I got out my clamp-on
DC ammeter and checked, it was pretty close. That site had
obtained power measurements for a number of video cards,
from somewhere. So it wasn't using the imaginative numbers
provided by the manufacturers either. The video card
power numbers were "xbitlabs" quality (but predated the
existence of Xbitlabs). And that made it a damn nice
power calculator site. But they didn't maintain
it, and eventually shut it down. It's a lot of work
keeping tools like that running properly. The Asus
one for example, should be a lot better, because they
have the engineers and technicians to do a good job.

Paul
 
A

Adam

Paul said:
Now you understand why I "bench test" on the kitchen table first,
before putting the system in the computer case.

You don't absolutely need *any* wiring to the front panel at all,
for a bench test. But what I do instead, is keep a push button switch
with two connector pins on the end, which slide over the PWR and Ground
pin pair. That's for turning the system on. I can also slip a screwdriver
tip between those two pins, to bridge them and start the system. That
requires a good deal of care and dexterity, and is only
practical when the motherboard is sitting on the kitchen table.

http://i61.tinypic.com/28bgwf9.gif

On the picture there, you can see that header has a "dangerous pair"
in the SPKR pin area. Don't bridge that +5V pin if you can possibly
manage it, to any adjacent Ground pins. It's another one of those
situations where there may be no protective fuse in the path.

*******

In the past, some Antecs have had wiring errors in USB or Firewire
cables (that's a 2x5 on the motherboard end, leading to a front
panel mounted connector). So I would not hook up the front panel I/O
wiring at all. On a couple Antec cases here (I have at least three
of them), I use the multimeter, set to ohms range, to verify the cable
wiring is correct. It's just easier to *not* use Antec front wiring, than
be bothered to do that. None of my Antec front USB ports are hooked up,
for this reason. I'm too lazy to correct the errors by moving the
pins around in the 2x5 end.

*******

I take it, OCZ had you do the "unconnected supply" test ?

For that one, you bridge PS_ON# to GND on the ATX cable.

Bringing the logic level low on PS_ON# is what makes
the supply fan spin, and the main supply section to function.
On page 37 here, that would be the green PS_ON# wire, to an
adjacent black GND wire. Some people recommend connecting
a dummy load to the supply, in the form of an old (scratch)
hard drive or something that draws a similar small amount
of power.

http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf

*******

This is a simplified model of the ATX supply. There are two
power generation circuits, and +5VSB is separate from the rest.

AC Input ------+--- +5VSB circuit
|
+--- +3.3/5.0/12V main section

When you switch the supply on at the back, the +5VSB starts to
produce power immediately. The fan will not be spinning at
this point. The +5VSB provides 2 to 3 amps max, and is
used as a supervisory voltage, amongst other uses. The
ATX power supply is convection cooled at this point, when
removing heat from the +5VSB circuit. Due to the modest
capacity of the +5VSB, it doesn't get too warm.

When the ATX power supply main cable has PS_ON# and GND
brought together, that grounds the pullup resistor on
PS_ON#. Normally, with a voltmeter, you'd see 5 volts
level on PS_ON#, and it's when that level is grounded
that the supply runs. The fan begins to spin, and the
main voltages begin to be produced. The motherboard
would be starting to POST at this point. The case
fans would be spinning.

If you attempt to start an ATX supply, and you see
the PSU fan "twitch" about a half inch of rotation,
that means the supply tried to start, but encountered
a serious short circuit (current overload) on the outputs.
To protect against burning any cables, the ATX supply
has latched off. Normally, you'd need to switch off at
the back, wait 30 seconds, switch on again, to make
another attempt to start the system. The reason the
supply "twitches", is the overcurrent is disabled
for the first 35 milliseconds, until the PSU has had
a chance to charge the output capacitors, and that
allows the fans to receive current for 35 milliseconds.
The fan blades can only "twitch" in such a short time
frame. If the "serious short" is present, when the
overcurrent detection is enabled at 35 milliseconds,
the power supply immediately shuts off the main section.

(The reason you wait 30 seconds, is to give any inrush
limiter time to cool off.)

In this diagram, the +5VSB is used to power the control
circuits. The motherboard logic "latches" the momentary
logic low level from the front panel switch, and drives
out a "steady" 0.0V level on PSON#. And that's what is
used to control the ATX supply.

+5VSB (0.0V level +5VSB
| means "run please") |
Pullup \_ Pullup
Resistor \ Resistor
| PS_ON# |
PWR X----+---- Motherboard ---- Open -------------------+- ...
control
/ logic Collector (to of
main
| GND X----+ Driver ATX + PSU
| | supply) |
section
(Front GND GND
Panel
Switch - normally open, momentarily close to operate)

By removing any USB panel header or Firewire panel header wiring
from the front panel to the motherboard, you're removing
a possible place for electrical shorts to happen. Wiring
up the PWR button from the front of the case (two wire twisted
pair labeled PWR and GND), gives you enough control to turn
the system on and off.

*******

On an Asus motherboard, there is a green LED which is wired
in such a way as to monitor for +5VSB. If the ATX PSU is supplying
+5VSB, and the main PSU cable is wired up, the green LED should
be glowing. And the LED should not flicker. It should be
a solid level for the entire time that the switch on the
back of the ATX supply is in the ON position. Asus provides
the LED, to tell you when it is safe to work inside the PC.
The LED must be completely extinguished, before you
work on RAM DIMMs or pull PCI Express cards, that
sort of thing. It takes up to 30 seconds for +5VSB to
drain, after the ATX PSU is switched off.

Paul
Thanks, Guru Paul !!

This is just a quick post since I will need some time to digest the info.
 
A

Adam

Edmund said:
Normally there are some leds on the mainboard giving info about its
status. Sometimes this is found in a manual.....
Stronger connection??? not likely the problem.

Edmund
Thanks, yep, I was looking through the mobo manual and
there are CPU_LED, DRAM_LED/MemOK switch, VGA_LED, etc.
Will be checking those out later.
 
D

DecadentLinuxUserNumeroUno

Oh boy, that's new to me. I'll see if I can find any "how to" links on
troubleshooting with a voltmeter.
You can buy a multi PS tester for PCs at Amazon or other popular
retailer that costs about $7 to $15 and you hook you disconnected PS
cable to it, and it gives voltages for all the ATX supply rails in the
spec.

Easy greasy...

www.amazon.com/Coolmax-Power-Supply-Tester-PS-228/dp/B002R06PGE

www.amazon.com/Coolmax-PS-228-ATX12V-EPS12V-Motherboard/dp/B004ZPB546

Halfway down the page on the second one is a whole row of them to
compare.
 
J

Jonathan N. Little

Adam said:
Thanks, yep, I was looking through the mobo manual and
there are CPU_LED, DRAM_LED/MemOK switch, VGA_LED, etc.
Will be checking those out later.
Also most motherboards have a speaker pins on the front panel header,
and they include a little speaker dongle that if you connect it you can
get post beep codes that can help.

As someone else mentioned did the CPU fan start? LED on motherboard
light up? HD spin up? Monitor get a signal or NO SIGNAL message?

As I said you should try with minimal connections...remove everything
except video and the connection to the "pwr sw" pins on the front
header. This narrows your search.
 
V

VanguardLH

Paul said:
When debugging a power problem, at system startup
the components don't draw "max power". Even a modest
power supply, mistakenly connected to a high power system load,
should get you to the BIOS screen.
I've seen where an underpowered or weak PSU (they get limp over time)
won't power up a system (to the POST screen) that is minimally
configured until the HDD is disconnected. Too much power draw on a weak
PSU means no boot or unreliable boot despite the PSU's fans will spin.
 
V

VanguardLH

mechanic said:
So send it back to the shop!
He did. Adam *is* the shop. Look at the specs he gave. Did that look
like a pre-built or OEM build to you?
 
V

VanguardLH

Paul said:
You don't absolutely need *any* wiring to the front panel at all,
for a bench test. But what I do instead, is keep a push button switch
with two connector pins on the end, which slide over the PWR and Ground
pin pair. That's for turning the system on. I can also slip a screwdriver
tip between those two pins, to bridge them and start the system. That
requires a good deal of care and dexterity, and is only
practical when the motherboard is sitting on the kitchen table.
If shorting the PWR pins on the onboard front-panel pins doesn't work,
and to test the PSU is okay, bypass the onboard logic for soft power up
of the ATX PSU. Short the PS_ON line (green wire: pin 16 on a 24 power
connector, pin 14 on a 20-pin connector) to a ground line (black wire).
See pinout at http://www.smpspowersupply.com/connector_atx_pinout.GIF.
The signal floats high but the onboard logic pulls that line low to tell
the PSU to power up. Shorting it to ground effects the same pull to low
state. If done while the PSU is disconnected from the mobo, some PSUs
won't power up until they sense a load, so attach an HDD.

Front panel power switches can go bad or be defective so the PWR pin
short is a good test; however, if that doesn't work, make sure the PSU
will come up if its PS_ON line is pulled low.
 
A

Adam

DecadentLinuxUserNumeroUno said:
You can buy a multi PS tester for PCs at Amazon or other popular
retailer that costs about $7 to $15 and you hook you disconnected PS
cable to it, and it gives voltages for all the ATX supply rails in the
spec.

Easy greasy...

www.amazon.com/Coolmax-Power-Supply-Tester-PS-228/dp/B002R06PGE

www.amazon.com/Coolmax-PS-228-ATX12V-EPS12V-Motherboard/dp/B004ZPB546

Halfway down the page on the second one is a whole row of them to
compare.
Thanks, added it to my wish list just in time for Santa. :)
 
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A

Adam

Paul said:
Now you understand why I "bench test" on the kitchen table first,
before putting the system in the computer case.

You don't absolutely need *any* wiring to the front panel at all,
for a bench test. But what I do instead, is keep a push button switch
with two connector pins on the end, which slide over the PWR and Ground
pin pair. That's for turning the system on. I can also slip a screwdriver
tip between those two pins, to bridge them and start the system. That
requires a good deal of care and dexterity, and is only
practical when the motherboard is sitting on the kitchen table.

http://i61.tinypic.com/28bgwf9.gif

On the picture there, you can see that header has a "dangerous pair"
in the SPKR pin area. Don't bridge that +5V pin if you can possibly
manage it, to any adjacent Ground pins. It's another one of those
situations where there may be no protective fuse in the path.

*******

In the past, some Antecs have had wiring errors in USB or Firewire
cables (that's a 2x5 on the motherboard end, leading to a front
panel mounted connector). So I would not hook up the front panel I/O
wiring at all. On a couple Antec cases here (I have at least three
of them), I use the multimeter, set to ohms range, to verify the cable
wiring is correct. It's just easier to *not* use Antec front wiring, than
be bothered to do that. None of my Antec front USB ports are hooked up,
for this reason. I'm too lazy to correct the errors by moving the
pins around in the 2x5 end.

*******
Okay, I have disconnected the Antec case's front I/O panel USB connector.

I take it, OCZ had you do the "unconnected supply" test ?

For that one, you bridge PS_ON# to GND on the ATX cable.

Bringing the logic level low on PS_ON# is what makes
the supply fan spin, and the main supply section to function.
On page 37 here, that would be the green PS_ON# wire, to an
adjacent black GND wire. Some people recommend connecting
a dummy load to the supply, in the form of an old (scratch)
hard drive or something that draws a similar small amount
of power.

http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf

*******
Yes, the "unconnected supply" test sounds like what I performed.
Short the green wire to a black/gnd wire in order to test that
the PS fan spins.

This is a simplified model of the ATX supply. There are two
power generation circuits, and +5VSB is separate from the rest.

AC Input ------+--- +5VSB circuit
|
+--- +3.3/5.0/12V main section

When you switch the supply on at the back, the +5VSB starts to
produce power immediately. The fan will not be spinning at
this point. The +5VSB provides 2 to 3 amps max, and is
used as a supervisory voltage, amongst other uses. The
ATX power supply is convection cooled at this point, when
removing heat from the +5VSB circuit. Due to the modest
capacity of the +5VSB, it doesn't get too warm.

When the ATX power supply main cable has PS_ON# and GND
brought together, that grounds the pullup resistor on
PS_ON#. Normally, with a voltmeter, you'd see 5 volts
level on PS_ON#, and it's when that level is grounded
that the supply runs. The fan begins to spin, and the
main voltages begin to be produced. The motherboard
would be starting to POST at this point. The case
fans would be spinning.

If you attempt to start an ATX supply, and you see
the PSU fan "twitch" about a half inch of rotation,
that means the supply tried to start, but encountered
a serious short circuit (current overload) on the outputs.
To protect against burning any cables, the ATX supply
has latched off. Normally, you'd need to switch off at
the back, wait 30 seconds, switch on again, to make
another attempt to start the system. The reason the
supply "twitches", is the overcurrent is disabled
for the first 35 milliseconds, until the PSU has had
a chance to charge the output capacitors, and that
allows the fans to receive current for 35 milliseconds.
The fan blades can only "twitch" in such a short time
frame. If the "serious short" is present, when the
overcurrent detection is enabled at 35 milliseconds,
the power supply immediately shuts off the main section.

(The reason you wait 30 seconds, is to give any inrush
limiter time to cool off.)

In this diagram, the +5VSB is used to power the control
circuits. The motherboard logic "latches" the momentary
logic low level from the front panel switch, and drives
out a "steady" 0.0V level on PSON#. And that's what is
used to control the ATX supply.

+5VSB (0.0V level +5VSB
| means "run please") |
Pullup \_ Pullup
Resistor \ Resistor
| PS_ON# |
PWR X----+---- Motherboard ---- Open -------------------+- ...
control
/ logic Collector (to of
main
| GND X----+ Driver ATX + PSU
| | supply) |
section
(Front GND GND
Panel
Switch - normally open, momentarily close to operate)

By removing any USB panel header or Firewire panel header wiring
from the front panel to the motherboard, you're removing
a possible place for electrical shorts to happen. Wiring
up the PWR button from the front of the case (two wire twisted
pair labeled PWR and GND), gives you enough control to turn
the system on and off.

*******
Okay, the Antec case's front I/O panel USB connector is no longer connected.

On an Asus motherboard, there is a green LED which is wired
in such a way as to monitor for +5VSB. If the ATX PSU is supplying
+5VSB, and the main PSU cable is wired up, the green LED should
be glowing. And the LED should not flicker. It should be
a solid level for the entire time that the switch on the
back of the ATX supply is in the ON position. Asus provides
the LED, to tell you when it is safe to work inside the PC.
The LED must be completely extinguished, before you
work on RAM DIMMs or pull PCI Express cards, that
sort of thing. It takes up to 30 seconds for +5VSB to
drain, after the ATX PSU is switched off.

Paul
Okay, sounds like what the mobo manual calls the standby power (SB_PWR) LED,
which lights up no problem whenever mobo is connected to PS so far.
 

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