PSU question

  • Thread starter Thread starter MA
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M

MA

Just bought a new PSU, a Coolermaster iGreen 500W one. Wanting to test it I
plugged it in and nothing happened. Should PSUs work when not connected to a
motherboard? I test Cisco PSUs like this all the time, so expected this to
work. Duff item or should I just wait till my motherboard arrives?

Cheers.
 
MA said:
Just bought a new PSU, a Coolermaster iGreen 500W one. Wanting to test it
I plugged it in and nothing happened. Should PSUs work when not connected
to a motherboard? I test Cisco PSUs like this all the time, so expected
this to work. Duff item or should I just wait till my motherboard arrives?

Cheers.
Click to expand...

The motherboard and PSU work together. Power switch (momentary contact)
connects through mainboard. When you short that switch (push the button),
mainboard passes through request to power supply to turn on. Then power
supply turns on, and (if OK) sends power OK signal back to mainboard. When
power OK signal is received, CPU wakes up and attempts to run POST program
stored in mainboard BIOS. If POST runs OK, then video card is initialized.
After video card is initialized, you should then have "video" on the monitor
(possibly showing memory tests and other mainboard information), and the
mainboard will look for OS to boot (usually from hard drive).

Or the short answer, it's foolish to try to test the power supply without a
mainboard, unless you have a power supply tester (they make those) -Dave
 
Mike said:
The motherboard and PSU work together. Power switch (momentary
contact) connects through mainboard. When you short that switch
(push the button), mainboard passes through request to power supply
to turn on. Then power supply turns on, and (if OK) sends power OK
signal back to mainboard. When power OK signal is received, CPU
wakes up and attempts to run POST program stored in mainboard BIOS. If
POST runs OK, then video card is initialized. After video card is
initialized, you should then have "video" on the monitor (possibly
showing memory tests and other mainboard information), and the
mainboard will look for OS to boot (usually from hard drive).
Or the short answer, it's foolish to try to test the power supply
without a mainboard, unless you have a power supply tester (they make
those) -Dave
Click to expand...

Makes sense! Thanks for the quick and detailed reply. I'm just glad I don't
have to find a spare chassis to test our Cisco power supplies every time I
need to.
 
MA said:
Makes sense! Thanks for the quick and detailed reply. I'm just glad I don't
have to find a spare chassis to test our Cisco power supplies every time I
need to.
Click to expand...

On an ATX supply, connect PS_ON# to an adjacent COM pin. Those signals
are on the main power cable. Some people do that with a paper clip.
But you should consider placing a dummy load on the supply, to draw
a bit of current. The power supply cannot regulate well, if there is no
load. Some ATX supplies actually list a minimum current on the label,
which is a hint that the regulation will be off. A couple old disk drives,
connected to the disk cables, is one way to load an ATX PSU.

I've built my own load box, which draws a bit more current. I use
a toggle switch between PS_ON# and COM, to make the load box turn
the supply on and off. Then, I can probe the output rails and
see if they are all reasonably close to the expected values.
It'll take about $50-$100 worth of components to make a
small load box, with a fan to blow over the resistors to
keep them cool.

Here is a schematic of an ATX supply:

http://www.pavouk.comp.cz/hw/en_atxps.html

On the output stage, the diodes can "push" current, but not "pull"
current. That is why a bit of loading, constantly "pulling" on the
rails, helps to keep the power supply output voltage in the
proper range. A power supply may have its own scheme for loading
the supply internally, but for maximum testing safety (i.e. do no harm),
a dummy load is a good idea. Especially if the supplies are
ancient, and not as well designed as modern ones.

*******
The latest ATX specs are here - i.e. "ATX12V V2.2"

http://www.formfactors.org/devlist.asp?FFID=-1&CatID=2
http://www.formfactors.org/developer\specs\ATX12V_PSDG_2_2_public_br2.pdf

Older specs are not listed, but are still hiding on the site.
For older computers, the pinout info here may be more appropriate.

http://www.formfactors.org/developer/specs/atx/ATX12V_1_3dg.pdf

And this spec is even older. This version has the 1x6 "Aux"
connector pinout, if you need it.

http://web.archive.org/web/20030424...org/developer/specs/atx/ATX_ATX12V_PS_1_1.pdf
*******

Paul
 
MA said:
Makes sense! Thanks for the quick and detailed reply. I'm just glad I don't
have to find a spare chassis to test our Cisco power supplies every time I
need to.
Click to expand...

On an ATX supply, connect PS_ON# to an adjacent COM pin. Those signals
are on the main power cable. Some people do that with a paper clip.
But you should consider placing a dummy load on the supply, to draw
a bit of current. The power supply cannot regulate well, if there is no
load. Some ATX supplies actually list a minimum current on the label,
which is a hint that the regulation will be off. A couple old disk drives,
connected to the disk cables, is one way to load an ATX PSU.

I've built my own load box, which draws a bit more current. I use
a toggle switch between PS_ON# and COM, to make the load box turn
the supply on and off. Then, I can probe the output rails and
see if they are all reasonably close to the expected values.
It'll take about $50-$100 worth of components to make a
small load box, with a fan to blow over the resistors to
keep them cool.

Here is a schematic of an ATX supply:

http://www.pavouk.comp.cz/hw/en_atxps.html

On the output stage, the diodes can "push" current, but not "pull"
current. That is why a bit of loading, constantly "pulling" on the
rails, helps to keep the power supply output voltage in the
proper range. A power supply may have its own scheme for loading
the supply internally, but for maximum testing safety (i.e. do no harm),
a dummy load is a good idea. Especially if the supplies are
ancient, and not as well designed as modern ones.

*******
The latest ATX specs are here - i.e. "ATX12V V2.2"

http://www.formfactors.org/devlist.asp?FFID=-1&CatID=2
http://www.formfactors.org/developer\specs\ATX12V_PSDG_2_2_public_br2.pdf

Older specs are not listed, but are still hiding on the site.
For older computers, the pinout info here may be more appropriate.

http://www.formfactors.org/developer/specs/atx/ATX12V_1_3dg.pdf

And this spec is even older. This version has the 1x6 "Aux"
connector pinout.

http://web.archive.org/web/20030424...org/developer/specs/atx/ATX_ATX12V_PS_1_1.pdf
*******

Paul
 
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