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Potentially Faulty PSU - No CPU Installed.

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June 15, 2012 9:59:06 AM

Ok so this is the first time I've made a custom PC where I haven't had ALL the components ready to build straight away (I don't have the processor, GPU, optical drive and HDD yet but I have the case, mobo and PSU.)

I have the mobo, case fans etc. and everything else all hooked up. That is, without the components I do not yet have.

When I power on the computer (just to check case fan connections), the PSU starts for about two seconds then stops. It then pauses for 5 seconds or so and powers on again for another 2. This continues as long as the machine is on.

I'm hoping this isn't a power supply issue but rather the system failing POST because there is no CPU present? I mean, I will have one soon but I just needed to check all my fans were hooked up.

If anyone needs any more info I'm happy to help, thanks!

TPrezzle
a b ) Power supply
June 15, 2012 10:04:01 AM

Definitely, it will not post without the CPU. Don't despair... the PSU needs signal from CPU to turn on as well so your PSU behavior maybe normal reaction to the lack of CPU.

I have not tried what you did before & honestly, I would not dare. What you have done may be harmless but in any case, it does not give much benefit either so I suggest to wait for the rest of the component, hook them up properly & then you can test.
June 15, 2012 5:26:09 PM

randomkid said:
Definitely, it will not post without the CPU. Don't despair... the PSU needs signal from CPU to turn on as well so your PSU behavior maybe normal reaction to the lack of CPU.

I have not tried what you did before & honestly, I would not dare. What you have done may be harmless but in any case, it does not give much benefit either so I suggest to wait for the rest of the component, hook them up properly & then you can test.


Ok, so is it normal for a sort of restart every time POST fails?....

(Sorry if there are several replies, I tried replying but didn't see them :kaola:  )
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a c 140 ) Power supply
June 16, 2012 2:09:49 AM

Yes, and he's telling you to not power up the sys anymore until you get the CPU installed. I don't know why you would do that.
June 16, 2012 2:42:41 AM

Yeah I tried the same thing, and felt like a noob when I found out why it didn't work. There are ways to test a PSU, but it's kind of ghetto and I wouldn't do it just for the sake of not catching on fire or damaging the PSU.

BUT, if you are that interested in testing your PSU, then YouTube "PSU Paperclip test"
June 16, 2012 7:34:35 AM

jpardo2 said:
Yeah I tried the same thing, and felt like a noob when I found out why it didn't work. There are ways to test a PSU, but it's kind of ghetto and I wouldn't do it just for the sake of not catching on fire or damaging the PSU.

BUT, if you are that interested in testing your PSU, then YouTube "PSU Paperclip test"
jump the green wire to a black wire :)  of course unplug the ATX connector from the motherboard!
June 16, 2012 2:51:51 PM

clutchc said:
Yes, and he's telling you to not power up the sys anymore until you get the CPU installed. I don't know why you would do that.


If you read the original post you would see that I was just doing it to see if my fans were hooked up properly. I have taken his advice and I'm not starting it anymore connected to the motherboard.

Paperclip test looks interesting though...
a c 271 ) Power supply
June 16, 2012 6:04:02 PM

The issue in your case is that POST did not fail, POST was unable to execute so the hardware got caught in a loop of feeding the system power(controlled by a relay on the board), waiting for the bootstrapper to start up, that then needs the CPU which isn't present so POST doesn't get to start and the system returns to its start state and tries again.


You cannot make any troubleshooting statements about a component might be bad because the system wont run when the system should not be running because it is missing a critical component. You got exactly the result you were supposed to, a non-functional system.


As for the paper clip test, it only tells you 1 thing, your PSU is not totally DOA which you already know because it was able to power the system up for a few seconds. Wait until the rest of your components arrive and you can build a proper system that should function before you start looking for issues. If you are looking for issues you will find something abnormal that would never cause an issue but is indeed abnormal.
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