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How To Test A Power Supply


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#1 haken_zell

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Posted 04 October 2008 - 02:44 AM

Hi, i just want to ask if how to test a power supply if its still working or broken.,using a tester or anything just to test if its still safe to use it or not..

i removed it from my friends PC, because his PC doesn't boot anymore, if i press the power button, the CPU will turn on but there is no output on the monitor, the lights on the CPU indicates that its reading, the keyboard light also doesn't light up when i press Num Lock button, so i decided to pull out the power supply but i dont know how to test it..or maybe i was wrong that is was the power supply?! :thumbsup:

good day and thank you... :flowers:

Edited by haken_zell, 04 October 2008 - 02:46 AM.


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#2 dc3

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Posted 04 October 2008 - 03:00 AM

The motherboard initiates the PSU by shorting out two wires, in order for you to test the PSU without the motherboard you will have to short out two wires in the bundle that attaches to the motherboard. The article below explains how to do this.

Testing PSU

The purpose of this procedure is to bypass the motherboard to test the PSU.

Caution:
This procedure will involve working with live 12VDC electrical potentials which if handled improperly may lead to electrical shock. Proper precautions should also be taken to prevent electrostatic discharges (ESDs) within the case of the computer. For safety purposes please follow the instructions step by step.

First, shutdown your computer. Then unplug the power cable going into your computer.

Once you have opened the case, touch the metal of the case to discharge any static electricity.

The connector of the PSU which connects to the motherboard is readily recognizable by the number of wires in the bundle. To disconnect it you will need to press on the plastic clip to disengage it and then pull the connector up and away from the motherboard. Please take notice of the location of the locking tab and the notch on the socket of the motherboard, this will only connect one way as it is keyed. This wire bundle will have a memory of the way it has been installed and will want to bend back that direction, you may have to play around with it to find a position that the connector will stay in the same position while you run the test.

Posted Image

From the top left to right the pins are 13-24, the bottom from left to right are 1-12.


Please notice that there are PSUs with 24 pin and 20 pin connectors, the location of the green wire in the 24 pin connector is #16, and the green wire in the 20 pin connector is #14. If you look at the connector with socket side facing you and the clip on the top the number one pin will be on the bottom left corner. This makes the pin out for the 24 pin connector from left to right 13-24 on top, and 1-12 on the bottom. The pin out for the 20 pin connector from left to right is 11-20 on top , and 1-10 on the bottom. If you look at the connectors you notice that these are sockets that fit over the pins on the motherboard where the PSU cable attaches, this is where you will place the jumper. For a jumper you will need a piece of solid wire about the size of a paper clip (20-22 awg), preferably a wire with insulation. It will need to be large enough to fit firmly into the socket so that it will not need to be held in place while testing. You are at risk of electrical shock if you are holding the jumper when you power up the PSU. Insert one end of the jumper into the socket of the Green wire, and insert the other end into the socket of any Black wire.

Once the jumper is in place plug the cord back in. If the PSU is working properly the case fans, optical drives, hdds, and LEDs should power up and remain on. I would suggest that you not leave this connected any longer than is necessary for safety purposes.


At this point you can use a DC Voltage meter to read the different rail Voltages. You will want to insert the black probe into any of the Black (-) sockets, and insert the Red (+) probe in the five different colored sockets, one at a time. Below are the five different colors and their corresponding rail voltages. The Voltages should be within about ten percent plus or minus of the given values.

Yellow +12VDC

Blue -12VDC

Red +5VDC

White -5VDC

Orange +3.3VDC

To reconnect the 20/4 pin connector unplug the power cord, remove the jumper, and reconnect the connector. Take a moment at this time to make sure that nothing has been dislodged inside the case.

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#3 haken_zell

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Posted 04 October 2008 - 03:26 AM

thank you for replying.. :flowers:

can i ask what is the purpose of bypassing the motherboard?!

is there a possibility that the motherboard is broken?! because when the power supply is connected to the CPU, all the leds and fans are working, except for the leds on keyboard, and it doesn't have output on the monitor..

about the procedure on testing the power supply, thank you but i think i cant do it :thumbsup: its dangerous i think for someone newbie like me..
is there any other easier way to test the power supply?

thank you..

#4 dc3

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Posted 04 October 2008 - 05:22 AM

Let me see if I have this right, you took a PSU out of another computer and installed it in yours, and the fans run when it's turned on, but you have no display on the monitor?

If the fans and LEDs are coming on then it sounds like the PSU is working.

We're at the point where we need to know the make and model of your computer, and the same for the computer that the PSU came from. Some manufacturers like Dell have a proprietorial PSU which has a different pin configuration than those used by other manufacturers. Usually the size of the PSU is different as well, the physical dimensions that is.

Does this PSU have the special connectors that the newer 20/4 pin units have? Is there a power connection next to the CPU?

Why did you need to change out the PSU to start with?

If you are not comfortable trying the test, don't do it.

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#5 haken_zell

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Posted 04 October 2008 - 09:09 AM

thanks again.. :thumbsup:

im sorry if i get you confused, i didnt put it in my computer, i havent tested it yet to another computer, i took it from my friends CPU because he is experiencing problems like what ive stated in my first post, when i press the power button of his computer, it doesnt have a output on monitor, but all the leds and fans on his computer are working except for the led on his keyboard..i dont know what is the brand of his computer but i will ask him, it was bought from USA i think and brought here in the philippines..

the brand of his power supply is ultra V Series ULT-400P...

thanks..

Edited by haken_zell, 04 October 2008 - 09:11 AM.


#6 hamluis

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Posted 04 October 2008 - 10:57 AM

If his (your friend's) PSU was suspect...the simplest thing to have done would have been to (temporarily) replace it with a known good PSU.

You have a desktop system, right?

Louis

#7 haken_zell

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Posted 04 October 2008 - 11:30 AM

If his (your friend's) PSU was suspect...the simplest thing to have done would have been to (temporarily) replace it with a known good PSU.

You have a desktop system, right?

Louis



hi Louis, thanks.. its one of my problem, im using a laptop thats why i cant test it using another computer..and i dont want to tell him to go buy another power supply because im not really sure if its he's power supply that is broken..

thanks

#8 elomont

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Posted 06 February 2009 - 11:19 AM

So, just to beat a dead horse:

If after removing the power supply from a computer, applying a jumper between the green and "any" black wire, then testing for a 12v on the yellow wire and coming up with no voltage whatsoever the power supply is shot?

#9 dc3

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Posted 06 February 2009 - 11:29 AM

That would be my conclusion.

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#10 elomont

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Posted 06 February 2009 - 03:26 PM

One other question...

I have two separate computers which I'm tinkering with for two different people.

The one is a HP Pavilion 8776c running Windows ME and I have no clue what the other one. I just know the latter is running Windows 98 and a Pentium II.

I was spelunking in each of the towers and noticed that the HP has an extra few wires that lead to a PS_FAN connector on the MoBo. The other machine does not have these. I removed the power supply from the HP and did the troubleshooting that was explained earlier in this thread, but I'm just wondering if those wires needed to be hooked up to the MoBo in order to get an accurate outcome. I have since reinstalled everything and have momentarily jumped the case switch (the one on the front of the case that you push to power on the unit) just to make sure it wasn't the switch. It did not start up so I'm assuming that the power supply is definitely dead.

I believe these (power supplies) are non-returnable so I'm trying to exhaust all avenues before purchasing a brand new one.

Thoughts?

Edited by elomont, 06 February 2009 - 03:27 PM.


#11 Sneakycyber

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Posted 06 February 2009 - 05:34 PM

If those wires are coming from the power supply and going to a fan connector port on the motherboard its to monitor the fan in the Power supply to warn you if it stops working. With the results you have provided I would suspect the Power supply is dead. :thumbsup:

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#12 elomont

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Posted 07 February 2009 - 02:29 PM

I just ordered a replacement 400w PS (the old one was a 200w) off of Ebay for $34. I will post back here after I get it up and running. Someone remind me if I forget.

#13 Sneakycyber

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Posted 07 February 2009 - 06:40 PM

Hope everything works out ok :thumbsup:

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#14 emucade

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Posted 07 February 2009 - 07:27 PM

there are products you can buy that plug into you PS harnes.
you can get for about $15.00.
you can find them at any computer store.
goot luck


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#15 elomont

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Posted 08 February 2009 - 01:42 PM

The link you provided emucade was a tremendous help! I'm being facetious.

Clarification would be great!

Edited by elomont, 08 February 2009 - 01:42 PM.





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