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My computer powered off the other day on its own, and now when I push the power button, nothing happens. My assumption would naturally be that the power supply is done (possibly well done) but is there any good way to test this before I buy a new one?
Sam Hoice
Posted 2009-08-17T17:46:26.873
Reputation: 383
34
Unplug the power supply from any of the components inside the computer (or just remove it from the computer completely).
USE CAUTION HERE (Though you'd only be shocked with a max of 24 volts)
Grant
Posted 2009-08-17T17:46:26.873
Reputation: 2 695
Fun fact: an ATX PSU is actually 2 psus in one case : the big one which can be turned on and off and a small 5V one that's always on and provides standby power. It is possible for only the standby part to fail, which will make the main PSU work when hotwired, but will still be useless in a PC, as without standby power the mobo could not turn the main part on. – Agent_L – 2016-07-15T14:18:28.570
@Agent_L Hence, step #5. Hot wiring is to check if the PSU is dead or if you have more checking to do. – Grant – 2016-07-16T23:37:36.663
@Grant My point is that the PSU can be working when hotwired, but still be dead for PC use. – Agent_L – 2016-07-20T09:09:58.423
@Agent_L We're saying the same thing. If hotwiring fails, the PSU is dead for sure. If it succeeds, move on to step #5 and keep checking. Nothing but a full test on every single wire can tell you if the power supply is good for sure (and even then, there might be an intermittently broken wire). Heck, you could cut off every wire except green and one black and hotwiring would still 'pass'. – Grant – 2016-07-21T16:27:17.810
I have two adjacent black wires... which one should I use? – Ohad Schneider – 2018-05-23T15:57:41.790
1@OhadSchneider Either is fine, both black wires go to the same place. – Grant – 2018-05-24T16:17:45.070
Perhaps you should add the (official) pin number for the green wire. And perhaps its official signal name. – Peter Mortensen – 2018-09-27T19:35:27.967
6
+1, I've done this a few times. Looks like this http://www.tallahasseelights.com/tech/fm_transmitter/fm-004.jpg
– hyperslug – 2009-08-17T17:58:26.3803Yup, I used to do this all the time when I worked at GEEK SQUAD. The managers didn't like it because the managers though the inside of the computer was ugly and customer's didn't want to see it. I did it anyway because it's a quick check to see if the mobo/power supply is dead and then they don't have to check in their computer for a week. – Grant – 2009-08-17T18:03:04.173
@ Grant - And that is why you no longer work for GEEK SQUAD... your'e too good for them. – J. Polfer – 2009-08-19T13:09:45.230
@sheepsimulator: Man, the stories I got from that place... – Grant – 2009-08-19T14:55:52.053
Awesome! Thanks, I'll check it out and see what happens. If you smell something burning, call 911... – Sam Hoice – 2009-08-25T16:25:01.657
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Most well-stocked geek-stores sell a "power-supply tester" that has all the appropiate connectors to plug each part of your PSU into, with spiffy LEDs indicating status of the various rails, connectors for IDE/SATA/floppy power cables, etc. They run ~$20 US.
Adrien
Posted 2009-08-17T17:46:26.873
Reputation: 1 374
2I recommend this if someone is not confortable with a multimeter or connecting wires as suggested. Otherwise, Grant's suggestion is the free way to do it without another computer to test it on. – Troggy – 2009-08-17T18:47:33.397
It's much quicker using those, they show you in a second if all of the connectors are fine; doing it by hand takes much longer, and can be a bit fiddly with something like a SATA power connector. – Dentrasi – 2009-08-17T19:14:06.557
Great point! I should have guessed that there was a device for testing this. If I had this problem more often, I'd be more inclined (and I'd be sad). – Sam Hoice – 2009-08-25T16:25:45.867
Does that mean I should be sad for having need for one? – Adrien – 2009-08-25T23:45:55.840
Should I be sad for not even knowing it existed? – That Brazilian Guy – 2013-10-18T15:27:18.903
5
You could try using a multimeter to check the +/-5V and +/-12V rails. Due to the switching nature of the power supply, you'll want to put a resistor in series with your probes while measuring.
J. Polfer
Posted 2009-08-17T17:46:26.873
Reputation: 2 234
@VaibhavGarg - what would you use as a resistance to test with? Just a standard resistor or ..., what value of resistance is enough to test against? Thanks. – pbhj – 2015-01-15T14:43:03.040
@pbhj A resistance of high enough wattage and value so that it does not burn out, and the value low enough to draw a meaningful amount of current. – Vaibhav Garg – 2015-01-16T03:45:54.197
Getting/learning how to use a multimeter with electronic products is a good thing to do, and part of becoming superuser-awesome. You can pick up a multimeter suitable for this work for less than a trip to McDonalds, and sometimes free after rebate. That said, the above answers are better. But don't forget the multimeter and its awesome. – J. Polfer – 2009-08-17T20:56:14.977
2Using a multimeter can sometimes give a false positive too. In my experiance, the most common failure mode for a PSU is the capacitors on the primary side. In this case the multimer shows the voltage to be just fine in an open circuit condition, but as soon as you draw any current, it drops to an absurdly low level. So you need a multimeters to measure voltage, and a resistance as a linear load and an accurate estimate of the loading characterstics of the mobo in order to draw any conclusions. – Vaibhav Garg – 2009-09-01T11:30:02.943
Typo: Multimeter – Vaibhav Garg – 2009-09-01T11:30:37.717
@Vaibhav - good point, I've added that to my answer. – J. Polfer – 2009-09-01T21:26:50.913
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To test the power supply unit, follow these instructions from Corsair in the Power Supplies FAQ:
My Machine doesn’t start up when I hit the power button, is the PSU faulty?
Disconnect everything from your PSU except for one single fan that should be connected directly to one of the Molex connectors. Then, get a small piece of wire, paper clip, or suitable object and short the green pin and a black pin on the 24-pin connector on the power supply. The voltage present is a very low signaling voltage so no worries of being shocked. Your PSUs fan should spin along with the fan you have connected to it. If this is the case, your PSU may not be receiving the power on signal from your motherboard and you should consider other causes of the problem you’re having.
When a computer is turned on, the motherboard electronically connects the green pin (power on signal) to any one of the black connectors (ground). This signals the PSU to start supplying power. By shorting these two connectors, you are testing the PSU to determine if it can turn on when signaled to do so. If this doesn't work, then the PSU has probably failed. More information what each pin does on an ATX power supply unit is available on Wikipedia.
bwDraco
Posted 2009-08-17T17:46:26.873
Reputation: 41 701
1
I have used one of the testers which showed a faulty supply to be good. The problem is the tester doesn't put a proper load on the PSU.
I replaced the supply and that fixed the problem. The voltage is OK if no load is applied. I serviced yachts for many years with 12 volt lighting. Corroded connections due to salt water are very common. Customers would return a new bulb and claim it was bad. I had to explain that 12 volts would show on their multimeter with the bulb removed, but this did not prove the bulb was bad. The corroded connection limited the current. Same principle.
user264843
Posted 2009-08-17T17:46:26.873
Reputation: 21
The information you wrote is certainly useful but it is not written as an answer to the question. Could you please edit your text so that it contains an answer to "How to test a power supply?" – pabouk – 2013-10-18T22:41:03.480
2Please tell me your Hard drives were "hot swappable"? – James Mertz – 2011-05-01T22:27:14.497
2Power supplies have a short-circuit cutout which resets after being disconnected for 30 seconds or so. Disconnect the mains supply to the computer completely and wait for at least 30 seconds. Reconnect it and try again. – Majenko – 2011-05-01T23:58:29.973
I can tell you that my hard drives survived. I can't tell you that they are hot-swappable (or else I'd be lying). – Sam Hoice – 2011-11-17T23:27:36.733