POWER SUPPLY CUTS OFF

[snail1]

Hi; I've got a 6 year old PC running Win98 that dies (no power) sometimes. I mean no fans, no lights, no beeps.
When it looses power the only way to restart the computer is to flip the on/off switch on the power supply from 'on' to 'off' to 'on'. Simply unpluging the power cord will not make it power up.
This may happen when I am doing nothing or it may happen when I am writting a CD. There seems to be no pattern with usage.
I am assuming that the on/off switch is resetting the power supply.
My question; does this mean that the power supply is bad or is it possible that some component(s) are trying to use too much power and causing the power supply to trip?

 

[IPTnewbie]

you need a multimeter to see the draw.

on the psu should tell how many watts it is. these days 500 watts is typical.

you may only have a 200watt in this box if youve added aditional periphereals the PSU will be overtaxed and run hot and as failsafe shut itslef off.

i recommend replacing it. psu r cheap. then again you may wish to replace this pc entirely depending on what your using it for.

liz

 

[snail1]

Thanks IPnewbie;
Actually this machine has a 400W power supply and pretty good hardware (AMD 1.33) for an older machine, I have replaced it with a new machine.
I just wanted to see if anyone knew whether or not other hardware problems could cause the power supply to shut down.
If my only problem is the power supply then I would replace it and make this machine a dual boot with Linux and Win98.

 

[fenix]

Why don't you try to isolate. Disconnect the floppy, and all drives other than the HD. See if it still happens. If not, hook them up one at a time.

If a drive has an intermittent power problem, it could possibly overload the psu and trigger the minimum voltage circuit in the cpu. Just a thought.

 

[edfair]

Your description would be enough for me to replace the power supply. But there is one issue. Flipping the switch (on the power supply itself) is the same electrically as pulling the power cord. So the effects should be the same. It may be that you have a problem with the switch itself.

If you had an overload the power would try to come up and the fans would start rotation until the crowbar shutdown happened. Generally 1/2 to 3/4 of a fan rotation before it stops. Since you don't have that description I would suspect that your problem is not overload.


Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[snail1]

Thanks to all;
I think I'll replace the power supply and test it a while and we'll see how it goes.
It's really too good a machine to just discard if it doesn't take much to fix it.


Thanks again.

 

[snail1]

To edfair;
I would have thought that the power supply switch and the power cord would gve the same result but they don't. I have tried several times to just unplug the machine for several minutes and then power up and it never works, but every time that I flip the power switch off & on it will then work.
I guess that it could be the power supply switch but it just seems odd that I never have to switch it more than one time for it to work.

Well thanks to all

 

[edfair]

Assuming that the power switch is barely making contact, when it opens removing the power cord and replacing it doesn't affect anything. Flipping the switch forces the contacts back together until they open again.
I made the possible connection because I've opened switches to clean contacts when spare parts were days away.
You could also pull the power cord, flip the switch, then plug the cord back in. May power up.
This is all conjecture. It might be one possibility.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[LawnBoy]

Another conjecture is that the switch shorts the input to the supply when in the off position, thereby draining all filter caps. I've seen this done in proprietary industrial equipment as a safety measure.

 

[westredd]

Im thinking why it powers off in the 1st place. Something worth doing is checking the vents that lead into the PSU and check that they are not clogged up with dust, preventing airflow , therefore overheating the psu and causing it to give up. just a thought, ive seen this happen before.

 

[paparazi]

I'm going to add a few more possibilties:

1) Leaking/bulging motherboard capacitors can produce very similar symptoms.
see:

http://www.badcaps.com

for description
2) Excessive dust build up in the CPU heatsink/fan unit and so overheating, reaching thermal limit in bios.
3) As this is a "Socket a" CPU then there is always the possibility that the heatsink has been fitted 180degrees out (the recess in the base of the heatsink must be positioned so it is over the cam box of the CPU socket)
Also , has it been installed with a small amount of heatsink paste (both the above with cause the CPU to overheat reaching thermal cut-out temp.

AND of course the power supply as suggested.

Martin

We like members to GIVE and not just TAKE.
Participate and help others.

 

[snail1]

Thanks to all replies.
Last week I cleaned the inside with compressed air, paying particular attention to the power supply and processor fan & fins. I powered up and the thing ran non-stop with no problems for a week before I shut it down!
This may well have been the problem, although it wasn't excessively dirty there was some dust builtup on the processor fan.
Also, I haven't re-installed the side to the case yet so it may have better cooling right now. The processor temp has not ever checked as 'hot' but I must reboot and check temp in bios which may allow it to cool down?
I am calling this project finished for now, at a later date I'll get back to it and work with the linux I installed on this computer.

 

[fenix]

Hi Snail,

About keeping your side off, just a few cents worth of info.

A computer case is designed to have the best cooling in the closed position. It has to do with how the airflows over the things that give off heat, and creating the most air turbulence inside to transfer the heat out of the case, whether you have a "positive" or "negative" type of airflow system. These words are mainly used for a reference, as a computer case is actually too porous to actually have any significantly different pressure inside of it than outside, especially with the type of fans that computers use.

 

[franklin97355]

fenix, I would agree with you for those cases built for companies like Dell HP and Gateway but most aftermarket cases are designed to be universal and have places for fans that can help or hinder the airflow inside the case. Running with the side off is not the best in the long run but will help diagnose bad case fan placement or too little airflow problems.

The answer is "42"

 

[fenix]

Hi Franklin, thanks for the reply.

I don't quite understand how you can diagnose an improper airflow problem if the system isn't in its operating
condition (with a side off). Maybe you are saying that one
can just observe how many fans there are, and where they are ?

I just posted initially because it seemed that snail1 was under the impression that he would have better cooling with the side off, as he wrote, "Also, I haven't re-installed the side to the case yet so it may have better cooling right now."

It's all about learning and helping each other

 

[franklin97355]

My point was that if the computer temps are lower with the side off (and maybe a household fan blowing into the case) you might look at the fans and their placement in relation to airflow.

The answer is "42"