# What causes a computer power supply to fail?

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#### Mark44

Joined Nov 26, 2007
626
Over the past couple of months, my home computer has been acting up. During bootup the computer start sequence would fail, right after the drive started to spin up. I found that if I turned off the "hard" on/off switch at the back of the computer (the one that's on the power supply), and turned it back on, I could get the computer to start, and it would run without problems. The problem seemed to me to be a power supply that was failing, so I figured that I would need to replace it shortly.

The first time I noticed any problems was when I tried to restart the computer after it had been put in stand-by mode, so I stopped using stand-by and would shut it down instead. Recently, I have started noticing the problem during bootup.

Yesterday morning, I was unable to get the computer to start up, even after three or four attempts using the trick that had worked before. On the way to work I bought a new power supply, and when I got home, installed it. The computer now seems to be working as it should. This leads me to believe that the old power supply actually was the culprit.

I should add that the computer is about two years old, and is one that I put together from parts purchased at a chain computer/electronics store (Fry's). The old power supply was 350 W, which I believe was sufficient for the machine. The new one is 500 W (the place I got it had only one model).

My question is: What would have caused my old power supply to fail after what seems a relatively short time (about two years). The MTBF for the new one is 50,000 hours, which at the rate my wife and I use this computer should last us 50 to 100 years. I don't know anything about the internals of a power supply. What are the parts that can fail?
Thanks,
Mark

#### gerty

Joined Aug 30, 2007
1,250
A lot of power supply failures are heat related. Is your fan running?
Is the power supply full of dust or other debris? Is the computer in a cabinet with little or no air circulation?

#### bertus

Joined Apr 5, 2008
19,944
Hello,

As gerty says heat is a great problem.
It can cause the capacitors to malfunction.
Also fast on and off switching of the powersupply could break it.

Greetings,
Bertus

#### SgtWookie

Joined Jul 17, 2007
22,201
One big cause of heat is allowing dust to accumulate in the computer.

About every three to six months, you should open up the case, and blow out the dust using dry compressed air, or those cans of compressed air you can buy at office supply stores. Don't allow the fans to be spun at high speed by the compressed air, as that can cause early bearing failure. However, try to get them as clean as possible. Use a wooden stick to keep them stationary while you're blowing on them.

#### CVMichael

Joined Aug 3, 2007
419
I have a question about that too

I do that sometimes (to blow the dust off), but I'm afraid that the freezing liquid/thing that the can sprays damages the componenets ?

#### CVMichael

Joined Aug 3, 2007
419
By the way...

One time my power supply failed because of one of my hard-drives...

The hard-drive malfuntioned, and it was taking a lot of power plus my other hard-drives, the power supply could not keep up and refuzed to start.

To find out what was couzing the problem, I removed each hard-drive one by one, and started the computer with one HD off, then another one off, and so on... to find out the one with problem.

But it was too late for the power supply, it started to make weird noises, so I replaced both, HD and power supply (to a more powerful one also).

Anyways... sorry to intrude with my boring story...

#### Wendy

Joined Mar 24, 2008
21,840
One big cause of heat is allowing dust to accumulate in the computer.

About every three to six months, you should open up the case, and blow out the dust using dry compressed air, or those cans of compressed air you can buy at office supply stores. Don't allow the fans to be spun at high speed by the compressed air, as that can cause early bearing failure. However, try to get them as clean as possible. Use a wooden stick to keep them stationary while you're blowing on them.
Not just bearing failure, the counter EMF generated by the moving blade can blow the solid state electronics inside the fan. Been there, done that. It's a reliable way to take out a fan, so Wookie's advice is excellent.

Long time ago my Dad's computer started making noise, it was the power supply fan. I asked him to stop using it the moment it became quiet. Instead he kept on using it, burning out the motherboard, the hard drive, the hard drive interface (blew about 4 of those because the hard drive was bad, but looked good for all of a minute, until the interface card blew), and of course, the power supply. I asked him why he did this (after basically building a new computer from scratch), the answer was, "I thought it fixed itself.". DOH!

Power supplies are cheap, compared to the rest of the computer. Having said that, if the fan is the only problem I won't hesitate to only replace it (NOT for amateurs).

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#### Mark44

Joined Nov 26, 2007
626
A lot of power supply failures are heat related. Is your fan running?
Yes, it was running. Besides the PS fan, there's one on the CPU and one of the fans in the computer case was hooked up (and presumably running).
Is the power supply full of dust or other debris? Is the computer in a cabinet with little or no air circulation?
I didn't open up the power supply, so don't know if it was full of dust. There was a small amount of dust on the fan blade itself, but very little inside the computer case. The computer is not in a cabinet, and there is nothing to block air intake to the fans.

#### ugierhia

Joined Oct 8, 2008
1
It has the isolation part,,, just check first the two IC there,, if it does not recieve supply from the primary, then it will not give output,,,, check for blotted capacitors,, it causes the output to drop or rise depending on the condition of the system.

#### chrissyp

Joined Aug 25, 2008
82
Hi
All the above are right,but don't forget to clean out the air intake at the front of the tower if that gets blocked the fan will not work properly .If you are buying a new power supply ,buy one that is about 50% more power output than you need this will ensure it has an easy life,especially if your tower is in a confined space with poor airflow .

#### S_lannan

Joined Jun 20, 2007
247
i have repaired 10 or so atx supplies in the last 2 years.
every one of them has had bad low esr caps on the secondary side of the supply.

I only picked them out by visually examining them (they were bulged and leaking electrolyte.

Replacing these capacitors fixed the supplies.

Computer power supplies generally have a good amount of over/under voltage sensing and primary side current sensing so well before the supply gets a chance to fry itself, it will shut down.

#### Wendy

Joined Mar 24, 2008
21,840
Only thing I'll fix on a power supply unit is the fan, anything else goes and I throw the whole unit away. Just got through fighting a bad unit on my boys, wasn't it's fault, the florescent light went out and took the supply with it. Had weird sympoms though, it wasn't all that obvious.

My point is they are relatively cheap compared to the rest of the computer, and having blown once I assume the rest of the parts aren't too far from failing. I do not get top of the line units, my average unit cost is between $16 to$35, depending on wattage, and their average lifespan is usually well over 3 years.

#### afaik

Joined Nov 2, 2008
22
Sorry for bumping this thread up but I believe it has some relevance to what I need to ask. I've come across a few atx power supplies with bulging capacitors. Since I can't use those psu, how about I take working capacitors from one bad ps and replace bad capacitors on the other? I know I can order new caps, but since I would have to have so many different rated caps, why not just hold on to these power supplies and salvage the working parts for use in other power supplies. I'm also interested in doing the same with motherboard capacitors, but can I use those caps for power supplies and vice versa?

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#### afaik

Joined Nov 2, 2008
22
Should I have posted this in another section?

#### jj_alukkas

Joined Jan 8, 2009
753
My supply is 4 yrs old, runs for plenty of time and has heavy load including graphics card, Lighting systems and about 4 fans... 2 I added myself.. Its why I guess runs cool... It doens't make much noise but I have to clean it frequently due to heavy air circulation.. But thats no prob.. System has 6 fans totally including cpu..

#### Wendy

Joined Mar 24, 2008
21,840
Should I have posted this in another section?
Whenever you want to open a topic that deals with your own problem it is always a good idea to start a new thread. You can refer back to the old one as a reference, but it saves a lot of confusion.

Trying to take over a thread is called hijacking, and is strongly discouraged here at AAC.

#### gregdevid

Joined Feb 4, 2009
18
Hi ,
All are right, the problem just because of heeat in your pc. Always put your pc in dust free place and also clean your pc once in a week.And check your pc cooling fan working properly or not.

#### roltex_rohit123

Joined Jan 1, 2010
72
Over the past couple of months, my home computer has been acting up. During bootup the computer start sequence would fail, right after the drive started to spin up. I found that if I turned off the "hard" on/off switch at the back of the computer (the one that's on the power supply), and turned it back on, I could get the computer to start, and it would run without problems. The problem seemed to me to be a power supply that was failing, so I figured that I would need to replace it shortly.

The first time I noticed any problems was when I tried to restart the computer after it had been put in stand-by mode, so I stopped using stand-by and would shut it down instead. Recently, I have started noticing the problem during bootup.

Yesterday morning, I was unable to get the computer to start up, even after three or four attempts using the trick that had worked before. On the way to work I bought a new power supply, and when I got home, installed it. The computer now seems to be working as it should. This leads me to believe that the old power supply actually was the culprit.

I should add that the computer is about two years old, and is one that I put together from parts purchased at a chain computer/electronics store (Fry's). The old power supply was 350 W, which I believe was sufficient for the machine. The new one is 500 W (the place I got it had only one model).

My question is: What would have caused my old power supply to fail after what seems a relatively short time (about two years). The MTBF for the new one is 50,000 hours, which at the rate my wife and I use this computer should last us 50 to 100 years. I don't know anything about the internals of a power supply. What are the parts that can fail?
Thanks,
Mark
Thats a good thing you did by purchasing more wattage SMPS. now look for any malfunctions in your computer components. if you are using AMD proceessor then your cooling requirement is more and you need to add an additional fan in the cabinet. dont keep the cabinet open. many problems arise due to dust and moisture. try not to keep computer in sleep/standby mode since it keeps everything working. shut it down or hibernate it. blow dust off the cabinet every 6 months. a 500 watt supply will work fine for you.

#### R!f@@

Joined Apr 2, 2009
9,647
Thats a good thing you did by purchasing more wattage SMPS. now look for any malfunctions in your computer components. if you are using AMD proceessor then your cooling requirement is more and you need to add an additional fan in the cabinet. dont keep the cabinet open. many problems arise due to dust and moisture. try not to keep computer in sleep/standby mode since it keeps everything working. shut it down or hibernate it. blow dust off the cabinet every 6 months. a 500 watt supply will work fine for you.
Hey rohit...
Mind checking which millennium you are in......

Why do you guys tend to post away without even checking the thread date....

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#### Zaraphrax

Joined Mar 21, 2009
47
I've had one that was plugged into a UPS die, which I promptly replaced. The replacement then blew after a day or two. After that, I decided to get my Dad (who's an electrician) see what was up with it. We then determined that the UPS wasn't provided proper sine-wave AC, it was a really weird wave form. This must've really upset the caps inside the PSU. I suppose it's the same sort of thing if you have a mains voltage dip or flutter, except constantly.

So after setting the PC up with a new PSU and a new UPS, that was one very expensive lesson learned. Cheap UPS = stay away.

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