Question Motherboard CPU_LED is on after cleaning my PC ?

[nFrostbite]

Just did some dusting of my old PC and now it doesn't properly boot, the CPU_LED on the motherboard is on.
I already did the following:

• Reseat CPU, GPU, RAM, PSU cables
• Tried another CPU on the same motherboard
• Removed CMOS battery for 10 minutes

Anything else to try before declaring the board dead?

System specs:
MBD: ASUS Z97-A
CPU: i7-4790K
GPU: EVGA GTX 1070
RAM: HyperX Fury 16GB
SSD: Crucial MX500 1TB
PSU: Corsair RM650x
Case: Fractal Design Define R4

 

[DaleH]

Just did some dusting of my old PC and now it doesn't properly boot, CPU_LED on the motherboard on.
I already did the following:
Reseat CPU, GPU, RAM, PSU cables
Tried another CPU on the same motherboard
Removed CMOS battery for 10 minutes

Anything else to try before declaring the board dead?

System specs:
i7 4790K
ASUS Z97-A
HyperX Fury 16GB
EVGA GTX 1070
Crucial MX500 1TB
Corsair RM650x
Fractal Design Define R4

What do you mean by 'properly boot'?

 

[Misgar]

How violent were you with your "dusting". Did you perhaps knock a small surface mount component off the motherboard or GPU card? Did you knock any electrolytic capacitors (if fitted) around the CPU VRM stages?

Did you observe proper ESD (Electro Static Discharge) handling procedures whilst cleaning, to avoid (potentially) giving static-sensitive components a fatal electric shock? Some semiconductors can be damaged from as a low as 100V discharge and static voltages in excess of 1000V are easy to achieve.

https://automotivetechinfo.com/2016/12/preventing-electrostatic-discharge-damage/

Did you unplug any PSU leads and fail to reconnect them properly?

Have you checked with a magnifying glass to see if any of the tiny metal contacts in the CPU socket are bent or missing?

I don't worry about a light coating of dust inside my old/ancient computers and leave well alone, but I would do something if they got this bad.

https://terablitz.com/hardware/how-to-clean-a-dirty-pc-diy/

 

[geofelt]

During the cleaning, did you remove the processor from the socket?
If so, you might have bent a pin re inserting it.

 

[nFrostbite]

What do you mean by 'properly boot'?

Black screen, fans all spinning

 

[nFrostbite]

How violent were you with your "dusting". Did you perhaps knock a small surface mount component off the motherboard or GPU card? Did you knock any electrolytic capacitors (if fitted) around the CPU VRM stages?

Did you observe proper ESD (Electro Static Discharge) handling procedures whilst cleaning, to avoid (potentially) giving static-sensitive components a fatal electric shock? Some semiconductors can be damaged from as a low as 100V discharge and static voltages in excess of 1000V are easy to achieve.

https://automotivetechinfo.com/2016/12/preventing-electrostatic-discharge-damage/

Did you unplug any PSU leads and fail to reconnect them properly?

Have you checked with a magnifying glass to see if any of the tiny metal contacts in the CPU socket are bent or missing?

I don't worry about a light coating of dust inside my old/ancient computers and leave well alone, but I would do something if they got this bad.

https://terablitz.com/hardware/how-to-clean-a-dirty-pc-diy/

I didn't notice anything come loose or any ESD as this isn't my first time cleaning, I only clean it when the build up gets big enough that it kicks out dust every time I start my computer.

 

[nFrostbite]

During the cleaning, did you remove the processor from the socket?
If so, you might have bent a pin re inserting it.

Nope, CPU and CPU cooler were still mounted when I cleaned it.

 

[Misgar]

I didn't notice anything come loose or any ESD

99 times out of 100, you're blissfully unaware of potentially causing ESD damage. The only time I've felt a static shock is when walking across a carpet in a large hotel and reaching out for a metal door knob.

At work, it was mandatory to observe full ESD handling precautions, including ESD work benches, ESD lab coats, ESD foot wear, ESD wrist straps, etc. This was for completed units as well as bare prinnted circuit boards.

You don't want airplane navigation and control systems or satellite electronics to fail, just because some technician zapped a module with static (and yes I know there is usually redundancy in aerospace equipment).

However, I think it unlikely your problem is due to ESD.

Have you tried a different PSU?

Have you tried the iGPU built into the i7-4790K instead of the PCIe GPU? Sometimes a blank screen is because the BIOS has reset back to providing output on the iGPU instead of the main graphics card.

There have been times when I've plugged my monitor cable into the motherboard iGPU output by mistake and been greeted with a blank screen.

I also recommend removing all system RAM apart from one stick and see if the system POSTs. If it does boot up, power off and fit the remaining DIMMs. Sometimes removing RAM "jump starts" awkward systems when clearing the BIOS fails.

What does the motherboard manual say about the CPU_LED? Does it provide any clues, apart from a CPU detection fault?

In these circumstances, I'd eventually swap all components over to one of my other LGA1150 boards, to see if the motherboard has failed, then search eBay for a similar second-hand board if necessary. Of course, there's no guarantee the replacement won't also have problems.

 

[nFrostbite]

99 times out of 100, you're blissfully unaware of potentially causing ESD damage. The only time I've felt a static shock is when walking across a carpet in a large hotel and reaching out for a metal door knob.

At work, it was mandatory to observe full ESD handling precautions, including ESD work benches, ESD lab coats, ESD foot wear, ESD wrist straps, etc. This was for completed units as well as bare prinnted circuit boards.

You don't want airplane navigation and control systems or satellite electronics to fail, just because some technician zapped a module with static (and yes I know there is usually redundancy in aerospace equipment).

However, I think it unlikely your problem is due to ESD.

Have you tried a different PSU?

Have you tried the iGPU built into the i7-4790K instead of the PCIe GPU? Sometimes a blank screen is because the BIOS has reset back to providing output on the iGPU instead of the main graphics card.

There have been times when I've plugged my monitor cable into the motherboard iGPU output by mistake and been greeted with a blank screen.

I also recommend removing all system RAM apart from one stick and see if the system POSTs. If it does boot up, power off and fit the remaining DIMMs. Sometimes removing RAM "jump starts" awkward systems when clearing the BIOS fails.

What does the motherboard manual say about the CPU_LED? Does it provide any clues, apart from a CPU detection fault?

In these circumstances, I'd eventually swap all components over to one of my other LGA1150 boards, to see if the motherboard has failed, then search eBay for a similar second-hand board if necessary. Of course, there's no guarantee the replacement won't also have problems.

Okay I just just fixed it by removing the CPU and lightly blowing out any unseen debris. Now I have another problem, after I shutdown the computer, the next boot up has intermittent self shutdown before I get to the post screen, then it tries to boot up again and and shuts down again then it repeats.

 

[Misgar]

removing the CPU and lightly blowing out any unseen debris

I have to ask, what makes you think there was any dust or other foreign objects lurking in the socket?

the next boot up has intermittent self shutdown before I get to the post screen, then it tries to boot up again and and shuts down again then it repeats.

It seems you haven't fixed the problem, but at least the system is partially working again, to the extent you see something on the screen from time to time.

Did you use a magnifying glass as I suggested and spend 5 minutes examining each and every one of the tiny spring contacts in the socket? If any of them are slightly bent out of position, you may get intermittent contact with the CPU. This could be the reason why you're still having problems.

As this photo shows, the spring contacts are very small and it's not always easy to spot if they're out of alignment. You may need to remove the motherboard from the case to get close enough to check. Use a strong light from different angles.

View: https://www.youtube.com/watch?v=dd_vhLd8ykc

CAUTION: It is very easy indeed to snap off bent contacts whilst you're trying to straighten them, thereby ruining the motherboard. It's not impossible to repair a broken contact, but you need a spare board to cannibalize and a hot air resoldering tool and fine tweezers.

Some contacts are not vital, e.g. power/0V because there are multiple contacts performing the same function, and one less connection isn't a calamity.

Other contacts are vital, e.g. memory bus, because there are no redundant contacts.

https://www.ifixit.com/Guide/How+to+Fix+a+Bent+Intel+CPU+Socket+Pin/140082