Last Updated on February 11, 2018 by Dave Farquhar
Sometimes when a computer refuses to power up, it’s due to the power supply going bad. Here’s a safe way to test power supplies.
One day my pastor called me up because he had a computer problem. He knew his power supply was dead but didn’t know what to do about it. So his computer’s mortal remains are sitting here amongst my moving boxes as I write.
The answer, of course, is to call Dave and ask him to look at it. And then Dave will plug his spare ATX power supply into the system and see if it powers up and doesn’t smell weird.
With my power supply, the system powered up and was fine. The Hipro 146-watt power supply that came in his system from the factory had given up the ghost.
But what do you do when you don’t have a spare ATX power supply and Dave lives too far away and is too busy moving and doesn’t owe you a favor?
You unplug all the power supply’s power leads. Then you pull the power plug from the back of the unit. Turn off the power supply’s power button on the back if it has one. Then you grab a paper clip. Bend the paper clip into a U shape. Find pin 14 (the green wire) and connect it to any of the ground wires (black). Make sure the paper clip is far from anything that it can short out. Plug the power supply back in. If necessary, throw the power switch in the back.
If the fan starts, the power supply is good and the problem is something else.
Most likely if it’s not the power supply it’s the motherboard. Or maybe you got lucky and the lead from the computer case’s power switch came disconnected from the motherboard. I’ve seen stranger things–like a BIOS chip in a friend’s 386 way back when that managed to creep halfway out of its socket and render the system unbootable.
Sometimes just pulling the plug and waiting 30 seconds or so fixes intermittent power-up problems. Some power supplies are more prone to this than others..
But in this case, the dinky 146-watt power supply had had it. I went to the nearest store, picked up a house-brand 300W power supply that fit, and all was good. For 20 bucks, he was back up and running again.
David Farquhar is a computer security professional, entrepreneur, and author. He started his career as a part-time computer technician in 1994, worked his way up to system administrator by 1997, and has specialized in vulnerability management since 2013. He invests in real estate on the side and his hobbies include O gauge trains, baseball cards, and retro computers and video games. A University of Missouri graduate, he holds CISSP and Security+ certifications. He lives in St. Louis with his family.
7 thoughts on “A safe way to test power supplies”
Thank’s for the troubleshooting tip.
Enjoyable and amusing.
Excellent, as always.
I enjoy everything you write, even the baseball stuff. And I don’t even understand that game.
You know, i dont think its worth it to me to do that. I would be way to afraid of shocking myself. Just make sure you turn the power off before you start unplugging things.. I had an attorney who thinks he knows a lot about computers go ahead and unplug his power supply while the system was still running.. Apparently as he tried to do it, the lights went out in the room he was in and the power supply made some black smoke. (his was an AT power supply).
That’s why you do things in the right order and pull the plug from the wall, and why you keep the paper clip away from you and anything else metal when applying the power. But we’re not talking high voltage here either. Jump-starting your car is a whole lot more dangerous than this procedure.
I’m experiencing a suspected power supply problem with a compaq presario 5280 (mitac 110watt supply). Fuse tests good and nothing is burned.
The supply connects to the motherboard via three connectors (six pins each) so as to provide 3.3v in addition to the other voltages. Seems to be some variant of the AT style – not ATX. I’m unable to determine how to activate “power on” for bench test- I’m not measuring any voltage at any pin and can’t figure out how the power on/off is achieved by the motherboard. Any help?
I have news! It took some time to figure it all out, but the problem turned out to be something very inexpensive. The startup resistor for the +5VSB opened up – hence no standby voltage for powerup purposes. Replaced the defective 390K resistor and it came back to life!
Your article here on testing power supplies was both interesting and inspirational. Thanks.
Ignore me, I am nothing but a stupid spammer trying to get some Googlejuice, but Dave came in and deleted all the links because my IQ is lower than the temperature of the room you’re sitting in and I’m too lazy to get a job like everybody else. Buying bottles of vitamin C at Target and relabeling them Paxil was my neighbor’s idea. He said something about that being a personal war on scurvy. I’ll bet that would be really funny if I was smart enough to know what that means. So don’t buy any of my stuff. If you’re really feeling bad and want anti-depressents without a prescription, buy a bottle of vitamin B12 instead. It’s cheaper and it’ll actually do something.
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