# pc atx power supply

#### avz

##### Member
Hi all
I have a pc power supply. when I switch it "on" it starts to work - the fan begins to rotate for a second or two and then it stalls. if I wait a minute and try again, it still remains the same. unplugging it from the mains for a few minutes didn't help. any ideas are welcomed.

#### microtexan

##### New Member
Are you talking about the PS alone or in the computer. Most PC PSs require a minimum load to run.

#### knaaphix

##### New Member
Try checking the power supply separately

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#### avz

##### Member
I did just that. the strange thing about it that sometimes it begins to work and sometimes not.

#### jpinball

##### New Member
Hi all
I have a pc power supply. when I switch it "on" it starts to work - the fan begins to rotate for a second or two and then it stalls. if I wait a minute and try again, it still remains the same. unplugging it from the mains for a few minutes didn't help. any ideas are welcomed.
Does it make a bad noise? The bearings in the fan may be shot, and may have caused overheating, which would cause it to shutdown, and take the fan with it.

Does it smell bad? It could be the power supply. Look at the board for obvious damage.

#### btcg

##### New Member
Hi all
I have a pc power supply. when I switch it "on" it starts to work - the fan begins to rotate for a second or two and then it stalls. if I wait a minute and try again, it still remains the same. unplugging it from the mains for a few minutes didn't help. any ideas are welcomed.
Clean the fan. (I noticed your only complaint is the fan)

If this doesn't repair it:

#### avz

##### Member
It has nothing to do with the fan

Thanks for your answers. first of all, there is nothing wrong about the fan. I've never said that the problem is the fan. second, the reason that I've posted the question was not about the money, I'm well aware about the cost of a pc power supply. the reason is that it puzzels me and would like to know and learn where the problem is.

#### mvs sarma

##### Well-Known Member
Does it make a bad noise? The bearings in the fan may be shot, and may have caused overheating, which would cause it to shutdown, and take the fan with it.

Does it smell bad? It could be the power supply. Look at the board for obvious damage.
Fan runs on 12V
we can't load 12V unless 5V is loaded. the entire control loop works on5V the most important need of a PC power supply. Now you add a 2 amps or so load on 5V , your 12V will start functioning and fan would run

#### jpinball

##### New Member
Building on Sarma's suggestion, do some board swapping to figure out if it is the power supply or the mainboard you are plugging it into.

Try a different powersupply on your main board. Does it work? Then your load is good and the power supply or cable connector is bad.

Or try the power supply on another main board, if it doesn't work then take the cover off and try to elimnate sections that are still working.

You may find the black resistor,transistor with three legs and no body,etc. Replacing it may not fix your problem. You may have to find out what caused the failure and fix that.

The molex connectors that attach to the motherboard and other components usually only rated for twenty connections or so, so per Sarma, check each of the 5V leads on the motherboard in a convenient location.

Mark

#### mvs sarma

##### Well-Known Member
Building on Sarma's suggestion, do some board swapping to figure out if it is the power supply or the mainboard you are plugging it into.

Try a different powersupply on your main board. Does it work? Then your load is good and the power supply or cable connector is bad.

Or try the power supply on another main board, if it doesn't work then take the cover off and try to elimnate sections that are still working.

You may find the black resistor,transistor with three legs and no body,etc. Replacing it may not fix your problem. You may have to find out what caused the failure and fix that.

The molex connectors that attach to the motherboard and other components usually only rated for twenty connections or so, so per Sarma, check each of the 5V leads on the motherboard in a convenient location.

Mark
perhaps it is simple to give some artificial load on 5V and manage.

#### jpinball

##### New Member
Just my own prejudice, Sarma. I have a stack of old PC's five foot high, but would have to go find something to load it down a different way.

A motherboard should be a proper load, no?

Excellent information.

#### harryperales

##### New Member
i've had similar problems with what you are presently experiencing. What i did was check the power supply for leaky capacitors and replaced them with good one's. now everything is back to normal to me. So, you might as well check your PSU for leaky capacitors and do the replacement.

#### avz

##### Member
It makes sense

Hi
have seen leaking(s) from electrolytic capacitors?

#### harryperales

##### New Member
in the case that there is no leaky or bloated caps that is visible, you have to check the capacitors 1 by 1, coz it's what i did to solve a similar problem.
GL to you, hope you solve the problem soon

#### longshot21771

##### New Member
I had same problem, visably there were a few leaky caps and they tested bad, replaced them pwr supply powered right up ran for 5 minutes then just shut off. Honestly cannot remember exactly what the parts I replaced are called but one of them is a double diode symbol ( I think it is called a Barrier Diode ? ) Fortunately I have several of the same powers supplies so I pulled the whole part loose from a parts pwr supply and reinstalled it into the other board works great no problems. All 3 of the componets have three legs and are square in shape and bolted to a heat sink 2 of them have the -->I<-- symbol ( double diode ) sorry about the sloppy art work, hope this helps.

#### prash

##### New Member
Atx power supplies require some two wires to be shorted (in the 20 pin connector) to be ON. separate smps from board.see what you get at 5 v. and 12v pins using a multimeter.add some bulb or so as a load to 5V as well as 12 v lines.if one of the o/p is low then there is some short in respective circuit.fan runs and stops that shows that the supply goes in protection.you may find some short in rectifier area(after the SM transformer). generally zener diode or cap.
Prash.