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Fans Spin then stop

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11 replies

by ibscoutr

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I am in the process of building a computer and ran into a snag. When I go to hit power, the fans spin a second and then stop. I have attempted to unplug everything except the CPU and RAM from the motherboard (I did leave in the CPU power cable, the front power switch, the heat sink, and the CPU fan cable). I do not get any POST beeps. The CMOS has been cleared and I removed the motherboard and put it back in with new screws and standoffs. The memory was also removed and each piece was tried in each slot. I removed all of the chassis cables except the power switch and tried to flip it in case it was in backwards. Below are the relevant specs:

Intel E6600
AeroCool CPU Fan
ASUS P5B
Corsair 1GB x 2 DDR2
650W ZeroDBA PSU

Could it be that the motherboard is fried? I do not have another CPU, MB, or PSU to eliminate them from possibility. Before I send parts back, I just thought I would inquire on this forums' excellent opinion. Thanks.

11 replies

by thechas

Here is what is happening.

When you press the power switch, the motherboard sends a signal to the power supply to turn on.

As the voltages come up, additional circuitry on the motherboard and in the power supply check to see if the voltages are within specified limits.

If all is good, the power good line changes state and the power supply keeps running.

You have the power starting up, but no power good signal.

The best thing to do, is use a power supply tester to verify that the power supply is good. The second best is to try a different power supply.

I assume that the clear CMOS jumper is in the "Normal" position.

Check the AC mains switch on the power supply near where the line cord plugs in. Is it set to the correct line voltage?
In the US, it should be set to 115/120.

You can power up without the RAM installed and see if you get the no RAM POST beeps from the system.

Without parts to swap, there is little else I can suggest you check.

Chas

by ibscoutr

Thank you for the ideas. I scrounged up a good PSU from someone and it did the same thing. It's good to narrow it down.

That was a great idea to check the voltage switch, but it was set at 115.

I also tried without the RAM and it still did the same.

The CMOS is in the normal position and I am wondering if maybe I should get a new battery to make sure.

I am guessing it is down to the MOBO or the CPU.

Thanks again for your quick reply, your help is appreciated.

by mjd420nova

Replacing the standoffs may be an issue. Were any providing a ground to the MOBO?? Or were some standoffs shorting the power supply?? Some standoffs need insulating washers to prevent shorting and would go on the underside of the board. Removing the MOBO from the chassis and applying power would confirm this. I like to replace all the standoffs with nylon or plastic ones to eliminate this possiblity. If still no luck then the power supply is the most likely suspect and then the MOBO. Good luck

by ibscoutr

Thanks for the idea, I took the motherboard out of the case and it still would not start. I also tried another PSU. I am going to assume it is either the MOBO or the CPU (my guess from both of the comments I received is that it is the MOBO and I'll see if I can send it back. Thanks for your help.

by ibscoutr

Thanks for your help, but it has been a long two months and I am still stuck. I have returned the CPU and the Motherboard, both are new. I tested the PSU with a purchased PSU tester. The PSU tester shows everything as good. I thought I have ruled out everything, so I am a little lost. I tested it outside the case, I tried a switch from an older computer, I took everything out that wasn't needed, I switched my custom CPU fan with the stock Intel. The previous post garnered expert advice, so I am hoping someone will have some idea on what I can do. Thanks.

by aaronlbloom

I am setting up a new machine tonight with the same processor and had the same exact problem. My search for an answer led me here, but this was a dead end. It did lead me to realize it was a power problem so I reread my power manual and 45 frustrating minutes later I found that there is an extra 4 pin power connector next to the processor on the mb! No such thing on all my previous single processor machines.
I plugged it in and all is well.

by thekonfuser

I was facing the same (or similar) problem about a month ago. It might sound a little strange but it helped me. Change the CMOS battery and see if it works. It did for me.

by alanonmac

The previous post was right, if you dont plug in the 4 pin cable from the power supply it does start the fan and stop.
These 4 pin come with some Antec power supplies

by ibscoutr

Thanks, your right, it was that. I feel like such a dunce! Thanks for all your help.

by waggishmab

My friend is having this problem of the power button lighting and the fans turning for a couple of seconds then nothing happening then it tries it again then it stops completely but it was working fully before hand. I've built PCs in the past and stuff but I don't really want to open it up unless this is pretty much guaranteed to work as I do not want to void the cover on it for him but he has assignments due in very soon and needs access to it

UPDATE: We opened it up and the 4 pin power connector was connected. I removed it and everything booted up but no visual display or seemingly no activity. Then put the cable back into it and the original symptoms occured.

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