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Configuration:

CPU: Intel Core i7-4790K

Motherboard: ASUS Z97-A ATX DDR3 2600 LGA 1150

RAM: Crucial Ballistix Sport XT 16GB Kit (8GBx2) DDR3 1866

PSU: Corsair RM750

When I turn the PC on, the CPU fan turns on for about one second. Also, the EZ XMP LED(XLED1) turns green for a second. This happens about every 3 seconds until I turn off the PSU.

I disconnected all the drives and GPU, but that didn't change anything.

The only time when the CPU fan turns continuously is when I unplug the 8-pin CPU connector from PSU, so that only the the 24-pin MOBO connector is plugged in.

Trying to fix this, I got a new PSU (same model), but that didn't help.

Sorry if I missed any details. I will be happy to provide them.

Any suggestions on how to troubleshoot this?

Update: Sorry, I forgot to mention in the original post that I had cleared CMOS a couple of times. That didn't help.

Update 2: Again, sorry I didn't explicitly mention in the original post that all the USB devices (keyboard and the mouse) had been unplugged for troubleshooting.

Update 3: Got another motherboard. Installed the CPU. It works. So, it looks like the motherboard was at fault. Now the PC won't recognize the old Windows system disk, but that's another story :)

user1566515
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    The first thing I would try is clearing the CMOS. Your motherboard isn't very happy about something. – Mr Ethernet Aug 08 '19 at 22:00
  • Sounds like a motherboard or cpu failure. – Moab Aug 08 '19 at 22:17
  • Im going to be a little nit-picky, but your title triggers me a little. Just because your PC worked for 4 years doesnt have any bearing on whether or not it will work now. – Keltari Aug 09 '19 at 19:30
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    @Keltari Many people have similar questions about new builds. I wanted to stress that this is a valid hardware configuration. – user1566515 Aug 09 '19 at 19:47
  • @user1566515 Im not sure what you mean by "valid." Either it works, or it doesnt. If something stops working, something broke, which doesnt make it any less "valid." – Keltari Aug 09 '19 at 20:25
  • @user1566515 whenever you have a couple of minutes, can you try testing your rig with all peripherals (USB etc.) disconnected, leaving just the power cable connected to the PSU? See if the the CPU fan continues to start and stop every few seconds when you turn the computer on or if that (and the mobo LEDs) behave normally afterwards. I don't think this will make any difference because the rhythmic starting and stopping of a CPU fan is associated with dead motherboards, but if you could confirm that you've tried removing the peripherals, for Cliff Armstrong's benefit, that would be great! – Mr Ethernet Aug 10 '19 at 00:34

2 Answers2

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The motherboard has suffered a catastrophic failure.

This was always the most likely possibility. The description of the CPU fan as rhythmically starting and stopping by itself almost always points to a failed motherboard (or one that needs a CMOS reset, which has already been ruled out.)

The failure rate for motherboards compared to CPUs is also vastly higher in general. I have had to replace over a dozen motherboards but have yet to come across a single CPU failure. CPU failures are rare as they have fewer potential points of failure than motherboards and almost always outlive them.

In terms of proof that it's the motherboard and not the CPU, the ASUS Z-97 manual actually describes how a failed CPU can easily be recognized by the illumination of a dedicated CPU POST-failure LED on the motherboard itself.

The manual also describes how if the motherboard does find an error with either the CPU, boot device, DRAM or VGA module, it will not reboot itself as is happening in this situation, but will simply keep the corresponding POST-failure LED steadily lit until the error is resolved. That's not what's happening here: it's continually restarting itself.

Everything points to a bad motherboard.

enter image description here

Mr Ethernet
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  • Thank you! This makes a lot of sense. Do you think it's also possible that both the motherboard *and* the CPU have failed? – user1566515 Aug 09 '19 at 13:35
  • I disagree with this because a short in any component, including usb/thunderbolt peripherals, could cause these exact symptoms. Only if every other component is eliminated would I consider it certain that it's the motherboard. It's important to remember the faults in one component can always masquerade as a failures in a more-central component if the circumstances are right. No component is truly independent of the others. For the same reason self diagnostics can only be used to tell you where to look first... they are proof of nothing. – Cliff Armstrong Aug 09 '19 at 21:43
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    @CliffArmstrong oh I'm sure the OP has already tried disconnecting all USB and other peripherals and got his system down to its core components by this stage of the troubleshooting process. – Mr Ethernet Aug 09 '19 at 22:23
  • @user1566515 it's almost certainly just the motherboard. Only something like a power surge or massive static electric discharge would be capable of simultaneously frying the CPU and motherboard. With either of those situations, generally what happens is that the motherboard fails before any harmful voltages reach the CPU. I'm not saying that CPUs aren't fragile, they certainly are, it's just that the motherboard and/or PSU are first in line: power surges come in through the PSU and static electricity usually enters via the motherboard's peripheral ports. The CPU typically survives. – Mr Ethernet Aug 09 '19 at 22:40
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    @CliffArmstrong after the OP confirms that disconnecting all USB devices and other peripherals makes no difference whatsoever, please feel free to remove your downvote. It's odd that you're downvoting the correct answer but didn't downvote the other answer, that went off in the completely wrong direction (recommended buying a PSU tester!) – Mr Ethernet Aug 09 '19 at 22:53
  • I'm sorry but my down vote is for your answer which is critically incomplete and very much *not* correct. When you amend your answer I will be glad to remove the down vote. It's not personal. From 20 years of experience in the business, I find even IT professionals often forget to eliminate peripherals. Assuming all users who will read this will not make the mistakes even IT professionals regularly make and incorrectly telling them they have to spend potentially hundreds of dollars based on that assumption is far more dangerous than incorrectly suggesting more diagnostics with a $20 psu tester – Cliff Armstrong Aug 09 '19 at 23:19
  • @CliffArmstrong I'm not answering the question for people in general, I'm answering it for the OP in particular, based on HIS situation and the manual for HIS motherboard. The problem in THIS situation is that the motherboard has failed. Read the relevant pages in the manual on POST-error LEDs. Read the steps the OP has already tried closely. It's intellectually lazy to pull rank and point to your experience (you don't know how much I have) when you could be reading the manual for the OP's actual motherboard and applying some common sense. A bad PSU won't cause these particular symptoms. – Mr Ethernet Aug 10 '19 at 00:07
  • You're taking this way too personally. I didn't "pull rank." You're right I don't know what your experience is *because you haven't shared it*. I was establishing that there is a solid basis for what I claim. And you are absolutely wrong... a bad PSU absolutely can cause these symptoms. We know it's not the PSU in this case because the OP has already eliminated it. But a bad PSU causing these symptoms is actually more likely that a motherboard failure. – Cliff Armstrong Aug 10 '19 at 16:41
  • @CliffArmstrong the OP's computer does not POST and he wants to know why. I quickly identified the cause and everything so far points to my answer being absolutely correct. There is a virtually *no* possibility that unplugging a USB device will solve this. Why? The OP has almost certainly tried it already. He has disconnected internal components, such as his hard drives and GPU. The peripherals were so obvious he most likely didn't bother to mention them. It's like turning it off an on again; it goes without saying. I have asked him to confirm he already tried it for your benefit. – Mr Ethernet Aug 11 '19 at 13:06
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    Sorry I didn't explicitly mention in the original post that all the USB devices (keyboard and the mouse) had been unplugged. The devices mentioned in the "Configuration" part (plus a monitor via HDMI) are the only "players" in my test. – user1566515 Aug 11 '19 at 21:14
  • @user1566515 thanks for confirming. I knew you had already tried that :) – Mr Ethernet Aug 11 '19 at 21:15
  • @wrecclesham No problem :) I'll get a new board in a few days will update this post. – user1566515 Aug 11 '19 at 21:16
  • Thanks for the update. Good luck with the transplant! – Mr Ethernet Aug 11 '19 at 21:18
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    Yes, it was the motherboard. Thanks again! – user1566515 Aug 14 '19 at 03:16
  • Glad I could help!! Cliffy, you might want to remove that downvote now... – Mr Ethernet Aug 14 '19 at 03:30
-1

ATX Power supply tester

can find mail order < $20

  • step1: u already did, disconnect everything & have just power supply and motherboard
    • if onboard video and looks like it's booting but nothing on screen then scrounge a working graphics card
    • if no onboard video, then try a second known working graphics card to rule out graphics card
    • goal is simply pass Power On Self Test and get the bios/efi screen to show on monitor
  • step2: if it's obvious that it's not making it that far, then it's narrowed down to either PSU or mobo
    • can try an ATX psu power tester, or try another known good working psu; goal again passing POST assuming mobo is good
    • if PSU checks out then assume mobo bad; if there are blinking led's representing an error code then track that down { for example some Dell's typically blink the power button led in a certain sequence to represent some error}

clearing CMOS via the mobo jumper is also a not a bad idea to try since it's easy to do... maybe make this step 1.5

ron
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  • I tried 2 PSUs, one of them brand new. It's pretty clear at this point that the problem is with CPU and/or mobo. The question is how to narrow it down. I don't know if it's possible without having spare CPU or mobo laying around. – user1566515 Aug 09 '19 at 01:19