How do I check if power supply for my PC is working? Heeeeeeeeelp!!!

[zalek]

Hello, I am trying to build a new PC. After connecting all the parts,
I turned the switch on and... nothing.
I suspect that the power supply is not working, or the circuit on the
motherboard that switches the power supply on is not working.
When I flip the switch on the back of the power supply on, the
keyboard LED turns on for a second. However, when I press the major
switch, nothing happens. No fans move, and there are no noises. I
checked the major switch with an ohmmeter, and the switch seems like
it works.
I'm not sure if the power supply or the motherboard circuit that
starts the power supply isn't working.
So my question is, how can I check if the power supply is working?
Thank you very much

Zalek

 

[Paul]

Hello, I am trying to build a new PC. After connecting all the parts,
I turned the switch on and... nothing.
I suspect that the power supply is not working, or the circuit on the
motherboard that switches the power supply on is not working.
When I flip the switch on the back of the power supply on, the
keyboard LED turns on for a second. However, when I press the major
switch, nothing happens. No fans move, and there are no noises. I
checked the major switch with an ohmmeter, and the switch seems like
it works.
I'm not sure if the power supply or the motherboard circuit that
starts the power supply isn't working.
So my question is, how can I check if the power supply is working?
Thank you very much

Zalek

There is a power supply spec here, so you can see the signal names.

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

To start with, the power supply is split into two pieces. The +5VSB
output, is available as soon as the rear switch is turned on. The +5VSB,
in turn, flows down the main power cable and powers some motherboard
logic.

The second half of the power supply, operates the 3.3V/5V/12V/-12V
outputs. The power is "soft switched" by means of the logic level
on the PS_ON# signal. The PS_ON# signal normally is pulled to +5V,
by an internal resistor. To start the supply, PS_ON# needs to be
grounded (zero volt level).

Inside the computer, the chain of command looks like this.

Front Motherboard Grounds Main To main ATX
Power ------------ Logic runs ----- PS_ON# --------------- part of supply,
Switch on +5VSB to operate Cable fans start to spin
(momentary (latches when PS_ON# is
contact) signal) grounded

An ATX supply can be operated on the test bench.

1) Connect a dummy load to the supply. You could use a couple old
hard drives, and connect them to the Molex connectors. I have
a home made load box that I use.

2) Switch on power supply at the back.

3) Connect Green to Black with a paper clip. The fans should spin.

Then, you can use a multimeter to measure the voltages if you want.
I use a load box, drawing a light load (<100W), to help ensure
that the power supply will be regulating properly when I measure
it. I actually test new power supplies, before I use them.

Paul

 

[zalek]

There is a power supply spec here, so you can see the signal names.

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

To start with, the power supply is split into two pieces. The +5VSB
output, is available as soon as the rear switch is turned on. The +5VSB,
in turn, flows down the main power cable and powers some motherboard
logic.

The second half of the power supply, operates the 3.3V/5V/12V/-12V
outputs. The power is "soft switched" by means of the logic level
on the PS_ON# signal. The PS_ON# signal normally is pulled to +5V,
by an internal resistor. To start the supply, PS_ON# needs to be
grounded (zero volt level).

Inside the computer, the chain of command looks like this.

Front Motherboard Grounds Main To main ATX
Power ------------ Logic runs ----- PS_ON# --------------- part of supply,
Switch on +5VSB to operate Cable fans start to spin
(momentary (latches when PS_ON# is
contact) signal) grounded

An ATX supply can be operated on the test bench.

1) Connect a dummy load to the supply. You could use a couple old
hard drives, and connect them to the Molex connectors. I have
a home made load box that I use.

2) Switch on power supply at the back.

3) Connect Green to Black with a paper clip. The fans should spin.

Then, you can use a multimeter to measure the voltages if you want.
I use a load box, drawing a light load (<100W), to help ensure
that the power supply will be regulating properly when I measure
it. I actually test new power supplies, before I use them.

Paul

Paul,
Thanks very much for answering. I understood your explanation - now I
know why the LED on the keyboard was turned on when I turned the back
switch on.

I'm not sure what you meant by "Connect Green to Black". I looked at
all the cables coming from the power supply, and I didn't see anything
green. Only yellow, red, white, black, blue, and purple.
Thanks again, I really appreciate the help.
-Zalek

 

[Paul]

Paul,
Thanks very much for answering. I understood your explanation - now I
know why the LED on the keyboard was turned on when I turned the back
switch on.

I'm not sure what you meant by "Connect Green to Black". I looked at
all the cables coming from the power supply, and I didn't see anything
green. Only yellow, red, white, black, blue, and purple.
Thanks again, I really appreciate the help.
-Zalek

If you check the formfactors.org PDF file, it has a pinout for the main
connector, with names and wire colors.

Pin Signal Color Pin Signal Color
--- ------ ----- --- ------ -----

1 +3.3VDC Orange 13 +3.3VDC Orange
[13] [+3.3 V default sense] [Brown]
2 +3.3VDC Orange 14 -12VDC Blue
3 COM Black 15 COM Black
4 +5VDC Red 16 PS_ON# Green <---
5 COM Black 17 COM Black
6 +5VDC Red 18 COM Black
7 COM Black 19 COM Black
8 PWR_OK Gray 20 Reserved N/C
9 +5VSB Purple 21 +5VDC Red
10 +12 V1DC Yellow 22 +5VDC Red
11 +12 V1DC Yellow 23 +5VDC Red
12 +3.3 VDC Orange 24 COM Black

HTH,
Paul

 

[Nicholas Sherlock]

Hello, I am trying to build a new PC. After connecting all the parts,
I turned the switch on and... nothing.
I suspect that the power supply is not working, or the circuit on the
motherboard that switches the power supply on is not working.
When I flip the switch on the back of the power supply on, the
keyboard LED turns on for a second. However, when I press the major
switch, nothing happens. No fans move, and there are no noises. I
checked the major switch with an ohmmeter, and the switch seems like
it works.
I'm not sure if the power supply or the motherboard circuit that
starts the power supply isn't working.
So my question is, how can I check if the power supply is working?
Thank you very much

Something really simple to check - Is the power button cable connected
correctly to the motherboard?

Cheers,
Nicholas Sherlock

 

[smlunatick]

Hello, I am trying to build a new PC.  After connecting all the parts,
I turned the switch on and... nothing.
I suspect that the power supply is not working, or the circuit on the
motherboard that switches the power supply on is not working.
When I flip the switch on the back of the power supply on, the
keyboard LED turns on for a second.  However, when I press the major
switch, nothing happens.  No fans move, and there are no noises.  I
checked the major switch with an ohmmeter, and the switch seems like
it works.
I'm not sure if the power supply or the motherboard circuit that
starts the power supply isn't working.
So my question is, how can I check if the power supply is working?
Thank you very much

Zalek

You can buy a power supply quick check tool.

 

[w_tom]

You can buy apower supplyquick check tool.

That power supply tester (quick test tool) is almost useless and too
expensive. But few reasons. A defective power supply can still boot
a computer AND will be reported as good by a power supply tester.
Second, a power supply tester does not report on other failed or good
component of a power supply 'system'. Paul has discussed some parts of
that 'system'

Anything a power supply tester might do is performed by the
multimeter. A defective power supply may only be detected when supply
is under full load from a computer. Meter will do that with a
definitive answer. Power supply tester will not.

Paul has recommended jumpering the green wire to black. Another
useful solution is to measure DC voltage of purple and green wires
both before and when power switch is pressed. Everything in a power
supply 'system' is known in less than 30 seconds by those measurements
and without disconnecting things. Even the power switch is tested. No
useful report is provided by that power supply tester. Disconnecting
may create further failures.

Numbers also make possible useful replies from the better informed.
A power supply tester means that additional assistance cannot be
provided. And finally, a meter means learning how that power supply
'system' really works. Quick tester teaches nothing useful.

 

[Sam Goldwasser]

You can buy a power supply quick check tool.

Try the power supply with a known working mainboard.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[larry moe 'n curly]

Hello, I am trying to build a new PC. After connecting all the parts,

You don't want to connect _all_ the parts and then test. You should
first connect just enough parts for a barebones system -- mobo, one
memory module, CPU, CPU cooler, graphics card (if the mobo doesn't
have built-in graphics), monitor, keyboard, power switch, reset
switch. Only after you prove that this will boot should you add more
memory, cards, drives, etc.

A common problem that prevents turning on the computer is a short
between the mobo and case, usually around one of the mounting holes or
at a corner (mobos and cases can be warped enough to let them touch --
always support the mobo near the corners, even with stick-on plastic
or rubber feet).

Make sure that the front panel power switch is connected to the
correct pins on the mobo. Not all mobos are labelled clearly for
this.

Unplug the PSU from all the computer stuff, and with it plugged into
the AC power and its rear switch turned on, measure for voltage
between a black wire and the purple wire. If you don't get something
close to +5V, the PSU is bad. Otherwise short the green wire on the
20- or 24-pin connector to any black wire (whaddya mean you don't see
a green wire??? It's between two black wires) to turn on the rest of
the PSU. While the black meter lead is connected to a black wire,
touch the red test lead to an orange (or brown) wire to check the
+3.3V DC, a red wire for the +5V, and a yellow wire for the +12V.
Don't be surprised if each voltage is off by quite a bit because
that's common when there's no load on the PSU. Also some PSUs won't
even start without a load, which can be provided by a hard drive or a
10-20 watt, 5-10 ohm resistor connected beween any black and red wires
(this resistor can get very hot).

PSU testers aren't very good and can indicate everything is OK even
when a voltage is way off. That happened when I tried a CompUSA brand
tester with a PSU whose +12V rail put out only about 10V and wouldn't
even spin the hard drive.

 

[zalek]

Thanks to everyone a lot for the suggestions.
In the meantime, I connected the motherboard with a known working
power supply, and still nothing happened. I also checked the original
power supply, as you guys suggested (connecting the green and black
wires) and the fan did start spinning. I also checked the voltage.
It showed 5.25 volts. I double checked the master switch, so it seems
that the problem is not with the power supply, but with the
motherboard.
Can you guys suggest anything I can test the motherboard with before I
return the motherboard?
Thanks a lot
-Zalek

 

[Sam Goldwasser]

Thanks to everyone a lot for the suggestions.
In the meantime, I connected the motherboard with a known working
power supply, and still nothing happened. I also checked the original
power supply, as you guys suggested (connecting the green and black
wires) and the fan did start spinning. I also checked the voltage.
It showed 5.25 volts. I double checked the master switch, so it seems
that the problem is not with the power supply, but with the
motherboard.
Can you guys suggest anything I can test the motherboard with before I
return the motherboard?
Thanks a lot
-Zalek

Double check the configuration of the motherboard - any jumpers and
other connections and that the CPU is plugged in correctly (if this
applies).

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[zalek]

Thanks to everyone a lot for the suggestions.
In the meantime, I connected the motherboard with a known working
power supply, and still nothing happened. I also checked the original
power supply, as you guys suggested (connecting the green and black
wires) and the fan did start spinning. I also checked the voltage.
It showed 5.25 volts. I double checked the master switch, so it seems
that the problem is not with the power supply, but with the
motherboard.
Can you guys suggest anything I can test the motherboard with before I
return the motherboard?
Thanks a lot
-Zalek

I just followed some suggestions, by removing the mb from the case and
connecting it to the powersupply and hard drive. again, no response.
I also noticed that one of the pins on the motherboard said RSVD_DNU.
My case comes without any wire named RSVD_DNU. I'm just curious, is
that important? And what is RSVD_DNU?
thanks again
-Zalek

 

[Michael W. Ryder]

I just followed some suggestions, by removing the mb from the case and
connecting it to the powersupply and hard drive. again, no response.
I also noticed that one of the pins on the motherboard said RSVD_DNU.
My case comes without any wire named RSVD_DNU. I'm just curious, is
that important? And what is RSVD_DNU?
thanks again
-Zalek

Not knowing what your motherboard manufacturer and model number is I
think the pins are ReSerVeD DoNotUse.

 

[Gurney]

Hello, I am trying to build a new PC. After connecting all the parts,
I turned the switch on and... nothing.
I suspect that the power supply is not working, or the circuit on the
motherboard that switches the power supply on is not working.
When I flip the switch on the back of the power supply on, the
keyboard LED turns on for a second. However, when I press the major
switch, nothing happens. No fans move, and there are no noises. I
checked the major switch with an ohmmeter, and the switch seems like
it works.
I'm not sure if the power supply or the motherboard circuit that
starts the power supply isn't working.
So my question is, how can I check if the power supply is working?
Thank you very much

Zalek

Why ask HERE? What does this have to do with the OS? NOTHING.

Ask elsewhere

 

[Baron]

Thanks to everyone a lot for the suggestions.
In the meantime, I connected the motherboard with a known working
power supply, and still nothing happened. I also checked the original
power supply, as you guys suggested (connecting the green and black
wires) and the fan did start spinning. I also checked the voltage.
It showed 5.25 volts. I double checked the master switch, so it seems
that the problem is not with the power supply, but with the
motherboard.
Can you guys suggest anything I can test the motherboard with before I
return the motherboard?
Thanks a lot
-Zalek

I assume that you have plugged in the four pin plug from the PSU to the
mainboard ?

 

[bebz]

Gurney, You could have just pointed him/her to the correct location. This
database is extensive and the savy at this know exactly where to go, those of
us who don't, look for the closest heading. And this is "Hardware" in Windows
XP.....

Bebz

 

[Gurney]

Gurney, You could have just pointed him/her to the correct location. This
database is extensive and the savy at this know exactly where to go, those of
us who don't, look for the closest heading. And this is "Hardware" in Windows
XP.....

Bebz

Sure, but questions regarding the PS have NOTHING to do with XP, so
the question does NOT belong here.

Where should they post? That's up the them. There are DOZENS of
forums that are active that relate to pure hardware.

 

[bebz]

Appreciate your reply and just to be clear, you are saying that if anyone has
questions regarding hardware not to come to Misrosoft Forums for
help/questions? Is this correct, or did I misunderstand your reply?

Bebz

 

[Malke]

Appreciate your reply and just to be clear, you are saying that if anyone
has questions regarding hardware not to come to Misrosoft Forums for
help/questions? Is this correct, or did I misunderstand your reply?

Excuse me Bebz, but you are having a conversation with a known troll.
"Gurney", as he is calling himself now (he changes names frequently
although this fools no one) has trolled the MS newsgroups for quite some
time now. He never helps but only tells posters that their posts don't
belong in whatever newsgroup they are in. In case you aren't familiar with
the term, here is a link explaining "troll":

http://en.wikipedia.org/wiki/Internet_troll

The only way to deal with trolls is "don't feed the troll". This means
ignoring them. They want you to respond because they need the attention.
You know that someone who does this sort of thing has to be mentally
unbalanced because a healthy person would never behave this way.

So don't feed Gurney. Killfile him and move on. Oh, and the rest of us are
happy for you to ask your questions here. If there is a better venue,
someone will tell you - not to be cruel or rude but merely to help you find
the answers you seek.

Malke

 

[bebz]

Excuse me Bebz, but you are having a conversation with a known troll.
"Gurney", as he is calling himself now (he changes names frequently
although this fools no one) has trolled the MS newsgroups for quite some
time now. He never helps but only tells posters that their posts don't
belong in whatever newsgroup they are in. In case you aren't familiar with
the term, here is a link explaining "troll":

http://en.wikipedia.org/wiki/Internet_troll

The only way to deal with trolls is "don't feed the troll". This means
ignoring them. They want you to respond because they need the attention.
You know that someone who does this sort of thing has to be mentally
unbalanced because a healthy person would never behave this way.

So don't feed Gurney. Killfile him and move on. Oh, and the rest of us are
happy for you to ask your questions here. If there is a better venue,
someone will tell you - not to be cruel or rude but merely to help you find
the answers you seek.

Malke
--
MS-MVP
Elephant Boy Computers
www.elephantboycomputers.com
Don't Panic!

Malke thanks for the input, I don't participate in discussion groups very
often so I am not familiar with the term. I will remember this, but I just
keep wondering that if you killfile him are you also not killfiling the
individual who asked the question? Where does he go from here if no other
input is entered? I am just a little confused...
Thanks again, Bebz