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Mobo won't power on - 8 pin CPU atx 12v?

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#1
Now here's what I've found: I can connect the 24 pin ATX power cable and the entire computer will turn on: the fans and everything else is running, all except for the CPU which isn't receiving power and the graphics card doesn't spin up. As soon as I plug the 8 pin ATX 12v cable that's supposed to power the CPU, the computer will no longer turn on. It'll turn on for a milisecond and instantly turn itself off.

I am using -

antec 900
fsp everest 800w psu
p5n-t deluxe mb
q6600 go
true 120 cooler
4 gb xms 2 corsair 800
320 gb seagate sata ii HD
bfg gtx 275 oc

so what could be the problem guys? Grounding issue?psu? Dead mobo or CPU?

What's the minimum you need for it to power up, for example would it power on without the graphics card in place?

It someones old system that I have bought so I know all the components have worked together.
 

theonedub

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#3
You will need a GPU since there is not an onboard solution. Try using the 4pin 12v AUX plug instead of the 8pin and see if it does the same thing. Are you sure the GPU is installed correctly and plugged in as well? As always try it with CPU, GPU, 1 stick of ram, no HD, and see if you can get it to enter the BIOS.
 

Mussels

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#4
mobo, PSU, ram, video card. Thats the minimum for a power on.

the fact that its turning on then off again, means its detecting something is wrong - likely, you forgot something.
 
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#5
Hi and thanks for the reply. It comes with two 4 pin plugs and I have tried it with both, and each one on their own all with the same result. Without any CPU power plugged in the psu fan spins, the case fans spin, the fan mounted to the true spins, the DVD has power, but the graphics card does not spin. When CPU power is added it turns on then instantly off
 
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#6
mobo, PSU, ram, video card. Thats the minimum for a power on.

the fact that its turning on then off again, means its detecting something is wrong - likely, you forgot something.
Hi mussels. I have 24 pin, 8 pin atx, two pcie 6 pins, case power switch connection, ram in place, case fans, CPU fan all connected... Anything I have missed?
 

Mussels

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#7
that list just confuses me :p


Motherboard: 24 pin, 8 pin, any aux power it needs (floppy/molex connectors, some boards have em)
Video card: all PCI-E power connected
Ram: one stick, try various slots. if no luck, try another stick in several slots.

During this, everything else should be disconnected. no HDD's, no DVD burner, no fans except for PSU, CPU and VGA.
 

theonedub

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#9
Unless that board has a feature where it does not power on if there is no fan connected to the CPU Fan header. Might want to check that out.
 

Mussels

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#10
Unless that board has a feature where it does not power on if there is no fan connected to the CPU Fan header. Might want to check that out.
^ what he said.

make sure the fan you use has an RPM sensor as well, or it wont detect it. (hint: use the fan from the stock cooler)
 

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#12
Also if I have no joy with the above suggestions is it worth setting the whole thing up outside the case to make sure the case is not shorting it out?
yes.
 
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#13
Ok just tried it all outside of the case and tried it with 4 different sticks of ram in all 4 slots individually. Exactly the same outcome :( but hopefully at least, that rules out any shorts happening inside the case. I also cleared the CMOS a few times just to check that as well. I have another psu arriving Monday so hopefully that may solve the problem or at least narrow the cause of the problem down a bit.
 

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#14
the only real thing left for you to do, is swap components with known good ones - test CPU, ram, PSU, and video card in another machine for example.
 
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#15
the only real thing left for you to do, is swap components with known good ones - test CPU, ram, PSU, and video card in another machine for example.
Yeah and that's where things really suck. I've had to wait ages to afford to get this and then this:( well hopefully I can eliminate the power supply tomorrow and then take it from there...I'm absolutely gutted but that's life I guess. Thanks for the help so far guys and I'll keep updating the thread with any success or findings.
 
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#16
hm .gif you haven't got the 8 pin mobo plug mixed up with your pciexpress plug? that would spell smokin mobo
have you tested the psu with a multimeter in situ?
 
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#17
View attachment 32693 you haven't got the 8 pin mobo plug mixed up with your pciexpress plug? that would spell smokin mobo
have you tested the psu with a multimeter in situ?
Nope no mix up on the plugs. Don't have a multimeter and can't really buy anything else at the moment so I'm stuck. Another member from the uk has said he will help by testing components on his system so will try new power supply tomorrow and if there is no joy I'll start posting him stuff to test out for me...that's if I can afford postage,yes, it's that bad.
 
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System Name not very good (wants throwing out window most of time)
Processor xp3000@ 2.17ghz pile of sh** /i7 920 DO on air for now
Motherboard msi kt6 delta oap /gigabyte x58 ud7 (rev1.0)
Cooling 1 green akasa 8cm(rear) 1 multicoloured akasa(hd) 1 12 cm (intake) 1 9cm with circuit from old psu
Memory 1.25 gb kingston hyperx @333mhz/ 3gb corsair dominator xmp 1600mhz
Video Card(s) (agp) hd3850 not bad not really suitable for mobo n processor/ gb hd5870
Storage wd 320gb + samsung 320 gig + wd 1tb 6gb/s
Display(s) compaq mv720
Case thermaltake XaserIII skull / coolermaster cm 690II
Audio Device(s) onboard
Power Supply corsair hx 650 w which solved many problems (blew up) /850w corsair
Software xp pro sp3/ ? win 7 ultimate (32 bit)
Benchmark Scores 6543 3d mark05 ye ye not good but look at the processor /uknown as still not benched
#18
shame ya don't live near me :ohwell:
 
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#20
I'm bored so I'm gonna remove the thermalright ultra and clean it. The idiot who shipped the computer left it attached so whilst I have it removed I'm going to check the CPU and socket for any damage. As I have only used amd previously is there anything that would signify damage to the processoer or the socket? also what's the best thing to use for cleaning the thermalright ultra, I was just going to use a cotton bud to clean all the dust of it, is that ok?
 

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#22
plug in the cpu 8pin,take out the graphics card, does it still turn off?
 

brandonwh64

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#24
YW. this problem seems like as i said in the other thread that it could be a bad motherboard or a corrupted bios but its hard to tell. if you can find another motherboard or CPU to test that would be best
 
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System Name not very good (wants throwing out window most of time)
Processor xp3000@ 2.17ghz pile of sh** /i7 920 DO on air for now
Motherboard msi kt6 delta oap /gigabyte x58 ud7 (rev1.0)
Cooling 1 green akasa 8cm(rear) 1 multicoloured akasa(hd) 1 12 cm (intake) 1 9cm with circuit from old psu
Memory 1.25 gb kingston hyperx @333mhz/ 3gb corsair dominator xmp 1600mhz
Video Card(s) (agp) hd3850 not bad not really suitable for mobo n processor/ gb hd5870
Storage wd 320gb + samsung 320 gig + wd 1tb 6gb/s
Display(s) compaq mv720
Case thermaltake XaserIII skull / coolermaster cm 690II
Audio Device(s) onboard
Power Supply corsair hx 650 w which solved many problems (blew up) /850w corsair
Software xp pro sp3/ ? win 7 ultimate (32 bit)
Benchmark Scores 6543 3d mark05 ye ye not good but look at the processor /uknown as still not benched
#25
ye it's a shame you don't live near here, as i would have been able to whisk that cooler of to my uncles garage, and use the air compressor to blast the dust out , if it's aluminium i would wash it under the tap then use a hair dryer to dry it out
 
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