View Full Version : New power supply

01-16-2003, 03:14 PM
Is it possible for a power supply to be bad right out the box? I bought a case for 30 (about $45) and the computer will not even turn on. Alternatively, is there an easy way to test if a power supply is bad?

01-16-2003, 03:56 PM
Welcome to http://www.pcguide.com/ubb/pcgubb.gif

Yes it is possible to be bad right out of the box and this is particularly true for power supplies that come with cases. Usually they are second or third rate to begin with.

The easiest way that I know to test is to try a different power supply and see if the system works. If you get nothing with one and the other works, administer last rites and either RMA or look for a replacement.

If you have a multimeter, you can use that to test the power supply, but I am guessing you don't have one handy.


david eaton
01-16-2003, 04:02 PM
Welcome to the http://www.pcguide.com/ubb/pcgubb.gif!

Yes, a psu can be DOA.

To check, you really need a multi-meter , so that you can check each individual power rail.

If nothing happens when you switch on, try shorting the GREEN and BLACK wires from the PSU. THis is where the power switch connects, and sometimes the actual case switch is faulty.
To see where the connections are, have a look at THIS (http://www.pcguide.com/vb/showthread.php?s=&threadid=19124) thread.

Have to be quick around here. Budfred, you beat me to it!


01-16-2003, 04:32 PM
The power supplies that are included in lower priced cases are notorious for being bad, either DOA or failing soon after being put into service.

01-16-2003, 06:03 PM
Thanks for all the suggestions; finally, I did get the power to come on, but it won't boot (of course!). The PC speaker beeps every 2-3 seconds, but nothing else happens. I feel like a bother, but any other suggestions would be appreciated.

01-16-2003, 09:16 PM
If you are getting a beep with no POST it suggests that the power supply may not be the problem after all. The beep is probably a beep code and you will need to determine what you BIOS is in order to figure out what it means. You can go here for more info:



01-17-2003, 01:58 PM
Hey all, I'm new to this forum today. I hate to muddy the waters for Tracer Bullet (initial question asker) but my problem is so similar but with one added detail. I started up my new home built computer and I didn't get power as well but I watched the fan on the power supply and it ran for just a millisecond and stopped. And I can reproduce this by turning the power switch off for a few seconds then trying again. I'm thinking bad power supply any of you experts seen this.

Smack me and tell me to start a new thread if appropriate!

Thanks in advance for the help,


01-17-2003, 05:15 PM

Welcome to http://www.pcguide.com/ubb/pcgubb.gif

The power supply is a likely culprit there too, but I would try a different one before going out and buying one if you can. The thing where the fan spin briefly and then stops can be from energy stored in the supply's capaciters, although I am not sure how they would be getting a charge in the first place. Another possibility that you might look at is that some systems are set up to not start if the CPU fan or power supply fan is not being read as working properly. Have you connected the CPU fan to the motherboard and any similar connector from the power supply to the mobo?


Paul Komski
01-17-2003, 07:17 PM
How does a capacitor supply DC?

Well, at a regular voltage, shall we say?

Sounds more like something is cutting-out or not enough amps.

01-17-2003, 07:25 PM
One of the main reasons that capacitors are used in a circuit is to provide a "buffer", and when powered down, store their charge for a period of time, powering on will discahrge them, thereby feeding the rest of circuit. If that stored charge is great enough, then they can breifly power a fan, by driving the rest of the ciruit.

Paul Komski
01-17-2003, 08:58 PM
Always open to correction or education - but thought the two main functions of capacitors in a PS were:- ones of small capacitance are used to reduce the ripple of rectified current and larger ones that have enough capacitance to bridge the 20millisecond power-down time of one cycle of normal mains current.

And why would powering-up discharge them when it would normally fire them up!

Please don't give me too much more homework to do.

Fruss Tray Ted
01-17-2003, 09:06 PM
Farad (http://dictionary.reference.com/search?q=farad&r=2) not 'capacitance'. Click on you homework!!! :eek: :D ;)

I also think that the motherboard should be double checked to see if all the necessary sensors are attached to allow the PSU to come on fully and not get powered down by the mobo that 'thinks' something is faulty.

Paul Komski
01-17-2003, 09:21 PM
He He :D There's microsoft and then there's microfarads. Smoothing capacitors have a capacitance of some 1000 microfarads and the storage ones above have a capacitance of some 50 times greater than this. Smoothing microsoft is probably impossible.

An uninteruptible power supply would be another ball park though.

01-17-2003, 09:32 PM
Originally posted by kevsterini
I started up my new home built computer and I didn't get power as well but I watched the fan on the power supply and it ran for just a millisecond and stopped. And I can reproduce this by turning the power switch off for a few seconds then trying again.My ECS K7S5A motherboard did the same thing and will not start up by jumpering the power button terminals on the motherboard. I just connected the green wire on the ATX power connector to ground and turn the computer on and off with a switch on a power control box. I did not feel like returning the board.

01-17-2003, 11:27 PM
[QUOTE]Originally posted by Fruss Tray Ted
Farad not 'capacitance'.
The term "capacitance" was used correctly in the previous posts.

How stuff works - Capacitors (http://www.howstuffworks.com/capacitor.htm)

Fruss Tray Ted
01-18-2003, 05:59 AM
Just razzin' Paul.

More homework? Darn and it's the weekend too!?! NO FAIR!

Paul Komski
01-19-2003, 04:08 PM
he he ... and I was so razz'd that my hair stood on end; must have been loads of static; hmmm ... now could static power a fan :D guess there would be some sparks to see.

Fruss Tray Ted
01-19-2003, 10:30 PM
It's been -22F lately....3 morns in a row last week. Not much warmer this morning either. No ESD's to really speak of and I wasn't near any 'pc'ripherals at the time anyway. I find it odd not to have the usual sparks around like other years seem to have?? :confused: Too crispy cold for me... :eek:

Actually Paul, I had a reply all made but refreshed the first window and found your second reply. I was feeling 'happy as a peacock' to be able to explain something to you instead of you to me? for once, but then realised in your second post that I wouldn't be telling you anything you did't know already, hence my razz post. (Beit an edited prior to,) reply. Did I say that right?

http://www.btc.gov.yk.ca/archives/winter/images/photos/3-3.jpg (http://www.btc.gov.yk.ca/archives/winter/en/view_image.php?c=harvesting&i=3)

Paul Komski
01-20-2003, 03:30 PM
He He - the truth is that its so wet and humid over here most of the time that static build up is a very rare event.

Nice pic - are those salmon maybe; just love smoked salmon. :)

01-21-2003, 03:25 PM
Thanks Budfred and others for your help. I tested the PS in a known good system and it fired and posted no prob. In my system I hooked up one stick of brand new memory and my processor and my processor fan. In my mind that narrows it down to the motherboard. I'm sending it back and getting a replacement. If I get the same issue with the new one I'll have to dig deeper.



01-21-2003, 06:03 PM

It certainly could be the motherboard, but it could also be the CPU or even another problem altogether. Before you send it back, you may want to take the motherboard out of the case, put it on a nonconductive surface and test with a minimal boot. This would include the CPU, power, video, one stick RAM, speaker, and keyboard. If you get POST or beep codes, you probably have a short or some other problem. Even if it stays dead, it would narrow it down to the CPU or motherboard. The only way I know to test that is to swap each. You put the CPU on a known good compatible board and see if it works and/or you put a compatible known good CPU on the motherboard and see if it works.