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How do you test a power supply to see if it's good?


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#1 Lee42

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Posted 25 July 2010 - 11:16 PM

I got a lot of used power supplies (& used pc's) and I have no idea if they're still good or not. How can I test them out? The only way I could think of is to plug them up (not installed in a system) and test the output DC voltage with a digital multimeter but I'm not getting any 12v or 5v voltage at all on any of them. Here's a picture of how I test them with a multimeter. http://img686.imageshack.us/img686/6738/img8046k.jpg

I trying to build some used systems (Dell's, Compaq's, eMachines, etc) but some of them are missing power supplies. And the ones that do have them, I don't know if the power supply is bad and the reason it wont boot up. For example, if I assemble an eMachine, and when I push the power button on the front and nothing happens and I don't see that little green l.e.d. light on the motherboard lit up, that kinda tells me the power supply is shot. I'm also thinking maybe the motherboard is shot...but I don't know how to determine either way.

With the power supply in a system and the power on, and it doesn't boot up or show any signs of life after I press the power button, could I maybe test voltage somewhere on the motherboard? I'd greatly appreciate any and all help.

Thanks in advance! :thumbsup:

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#2 MrBruce1959

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Posted 26 July 2010 - 02:05 AM

Hello and welcome to Bleepingcomputer.

Below I an going to post some directions for you to follow, then I am going to provide you with a link to a web site which will further help you with information that should be helpful for testing power supplies and all the connectors they have and what their output voltages would be if you tested them with a VOM meter.


WARNING: THIS POST MAY CONTAIN DIRECTIONS THAT INCLUDE WORKING WITH LIVE VOLTAGES OR PARTS INSIDE A COMPUTER'S POWER SUPPLY THAT CAN CAUSE SERIOUS ELECTRICAL SHOCK OR SERIOUS BURNS, A POWER SUPPLY CONTAINS VARY LARGE ELECTROLYTIC CAPACITORS THAT ACT JUST LIKE A BATTERY OR VOLTAGE STORAGE DEVICE, THOSE AND OTHER ELECTRONICS FOUND INSIDE A POWER SUPPLY CAN STORE DANGEROUS AMOUNTS OF ELECTRICITY HOURS OR EVEN WEEKS AFTER ALL ELECTRICAL CURRENT HAS BEEN DISCONNECTED FROM THEM! PLEASE USE EXTREME CAUTION AND COMMON SENSE WHEN WORKING WITH POWER SUPPLIES OR AC VOLTAGES!


The purpose of this procedure is to bypass the motherboard to test a ATX PSU. Some manufacturers Like Dell have used some non ATX PSUs which have a different pinout for the 20/4 pin connector, please confirm that your PSU is a ATX type before using this procedure.

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
www.playtool.com

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.

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.


Now here is a link to the web site to which you can use this page to determine a connecters power output by using a VOM multitester

http://www.playtool.com/pages/psuconnectors/connectors.html

More information here http://www.playtool.com/pages/psucompat/compat.html


Hope you find this information useful and educational as well.

Bruce.

Edited by MrBruce1959, 26 July 2010 - 02:07 AM.

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#3 Lee42

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Posted 26 July 2010 - 08:49 PM

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.

Hi Bruce. Thank you so much for helping me out! Your post was very informative, educational, and I was very happy to finally learn how to test a power supply! :thumbsup:

With one PSU on the bench (not installed), I jumped the green wire to a black one, hooked up my multimeter, put power to it, the fan came on and I got a reading on the meter. I was ecstatic needless to say. Here's a picture of my doing that: http://img838.imageshack.us/img838/6356/img8058.jpg

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.

I tried testing one that was installed in an eMachine and I got voltage on the meter and the PSU fan was running but the case fan, drives, and led's did not power up. Here's a pic of that: http://img64.imageshack.us/img64/1219/img8072q.jpg I even checked each connector going to the hdd & dvd drive and there was voltage. Oh btw, during this test, all cables were unplugged (monitor, mouse, etc.) and I didn't press the power switch at all.

So since you said the case fan should be running, I unplugged the fan connector at the motherboard (mobo) and checked voltage (see pic: http://img821.imageshack.us/img821/7901/img8073s.jpg ) but there was no voltage which makes me think the mobo is shot. What do you think? I am gonna test this method out on some other "no signs of life" systems and see what happens.

Thanks again Bruce for all your help. :flowers:

Edited by Lee42, 26 July 2010 - 08:51 PM.


#4 Baltboy

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Posted 26 July 2010 - 08:56 PM

Or you could go to Best Buy or online and buy a power supply tester for a few dollars. It tests all the voltages on the main power, fires everything up and they usually have connectors for all of the various power plugs as well.
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#5 Lee42

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Posted 26 July 2010 - 10:12 PM

Or you could go to Best Buy or online and buy a power supply tester for a few dollars. It tests all the voltages on the main power, fires everything up and they usually have connectors for all of the various power plugs as well.

I'll definitely go to Best Buy and look into that. Thanks for telling me about them. I didn't know they sold them there.




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