PC turned off after loud 'pop' - won't boot

Hi all,

Been handed my mother's desktop PC (that I originally built 10 years ago). There was apparently a loud 'pop' and the monitor went blank - it turns out the computer had turned off (obviously) and would not boot.

I only get a slight 'wobble' from the CPU cooler fan when I hit the power button. I bought M/B speaker, which emits no sound when boot is attempted.

Specs:

• Intel i3 2125
• Asus H77-I Motherboard
• Corsair 2 x 2GB DDR3 1333Mhz RAM
• Cooler Master Geminii M4 CPU Cooler
• Cooler Master Elite 120 mini-ITX & 500W power supply (bundled together)

Steps Attempted:

• Disconnected all Sata devices, fans and other cables
• Removed motherboard assemble from case (tried boot by shorting the power pins)
• Removed CPU cooler and cleaned off all thermal paste
• Tried each RAM stick in channel A1
• Tried a second hand PSU
• Shorted both PSUs (24-pin green wire to a black wire) with a paperclip - fans turn
• Examined the M/B by eye for any leaking capacitors or other damage (though I am no expert)

Current Status:

At this stage I am thinking it is likely a motherboard failure. The one caveat is that when I removed the CPU cooler, I discovered to my horror that I clearly had never removed the sticker from the base of the cooler.   I have built several PCs in my time am frankly ashamed to admit that on a forum...   Anyway how it worked for 9 years without overheating / needing thermal paste replacing is beyond me.

A loud pop usually indicates a chip has blown.  An inspection of the MOBO may reveal a bad chip.  

Not really my area of interest, I'll own, but that sounds to me like summat in the PSU blew.....and probably took out the mobo's main power caps along the way. I spent a few years assisting our works 'sparky', 20-odd years ago; I know ALL about what "blowing", overloaded components sound like, trust me!

Some of our experts will no doubt be along soon...

Mike. 

If you have the skill and the knowledge and the tools it is worth checking all the PSU outputs.

Bear in mind that supply to the Mobo  / CPU needs to be tested under load to be sure but 0V is 0V so that's where I'd start.

Any sign of burning or swelling around any capacitor is a sign of failure. The classic brown spot on the cap is a sure sign.

Opening the PSU is not advised as there are mains voltages within.

Current Status:

At this stage I am thinking it is likely a motherboard failure. The one caveat is that when I removed the CPU cooler, I discovered to my horror that I clearly had never removed the sticker from the base of the cooler.    I have built several PCs in my time am frankly ashamed to admit that on a forum...    Anyway how it worked for 9 years without overheating / needing thermal paste replacing is beyond me.

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The CPU has mechanisms to ensure that it will never heat up beyond a certain point (often around 100 degrees c) which manifests as thermal throttling - the CPU clocking down to prevent heat rising further, or in the worst cases immediate shut off.  This slow down when happening would be pretty obvious to a gamer or perhaps a more experienced computer user, but possibly some users would never notice unless the system was almost crawling to a halt.

FWIW if the PSU is good, I think it's most likely that something on the motherboard has blown.

Current Status:

At this stage I am thinking it is likely a motherboard failure. The one caveat is that when I removed the CPU cooler, I discovered to my horror that I clearly had never removed the sticker from the base of the cooler.   I have built several PCs in my time am frankly ashamed to admit that on a forum...   Anyway how it worked for 9 years without overheating / needing thermal paste replacing is beyond me.

Ouch! I've never heard of that one before. You learn something new every day. Make sure after you remove it to clean everything off

with (minimum) 95% isopropyl alcohol. Thoroughly. Adhesive from any sticker will really mess up the connection between the

thermal paste/cooler and the CPU.

After that, I strongly urge you to look at this site to get a feel for whether capacitors blew on the motherboard. About 10 years

would be a common time for some to die.

https://www.badcaps.net/index.php

You'll want to look at the "How to Identify" section for photos to help you know what to look for.

If caps are bad, they can be replaced if someone has soldering skills, but it's probably not worth the effort on a board that old.

That "pop" was something shorting out ~ If it is old enough (10 years, you say) or dirty enough, it could be anything. It could even have been something in the monitor ~ Don't forget to check that ~ I wouldn't be over worried.

Time to give her an early Birthday Present/Easter Egg. (Lots of Brownie Points)

Your Time Zone suggests you're UK or European ~ £200 should get her something that looks really snazzy and if you think that she would have difficulty with Windows 10, There's plenty of Desktop Emulation Apps out there.

 I bought M/B speaker, which emits no sound when boot is attempted.

 

You will not get any error beeps from a lifeless MB which by your "I only get a slight 'wobble' from the CPU cooler fan when I hit the power button" description it sound like you have 

Being that you have already tried a replacement PSU the MB being bad is the likely outcome, see Badcaps info here with some example pics of what to look for, right hand side of the page.

As Shplad suggested, check your capacitors. You have an older unit, and a few years ago there was a wave of caps blowing out because they were using cheap liquid electrolyte that eventually blew out the casing. Caps look like small, "Quaker Oats" (cylinders) up on end. If you see any "crud" on top or running down the side, that cap is bad. Also, the tops should be flat, it they are bulging up that cap is bad. One that has exploded should be obvious.

Hi everyone,

Thanks very much for your suggestions and advice.

I examined the M/B more closely today and found no evidence of capacitor damage (either bulging or leaking). I re-seated the CPU, re-installed the RAM etc. just to test again. No change.

I also tested the power delivery of both PSUs. Both showed roughly the right voltages although the original PSU was quite far out on the 5V and 12V rails. The 5V tended to measure 5.4-5.6V (i.e. a bit high) and the 12V measured 10.4V or 11.3V. The second PSU measured much closer (within 0.1-0.2V, which I'm assuming is within tolerance). I am starting to wonder if a PSU issue might have caused a M/B issue.

Is there any likelihood that it could be the CPU instead of the M/B? Reason being I have seen Sandybridge/Ivybridge CPUs on eBay for as low as £15 Buy It Now, but for a replacement (especially a miniITX one) I might as well throw away everything and start with a more modern LGA1151/AM4 platform bundle! (or purchase a refurb Dell/HP/Lenovo SFF as suggested).

Yes, if I recall correctly, motherboards are designed to tolereate +- 5 %  variance

in voltage. More than that and you might cause problems.

Before you go building an entirely new system, why not try mjd420nova's great

suggestion and plug it into another monitor? Or are you sure nothing is powering

on?

By the way, you can't always see capacitor damage. Just because you can't see

bulging or leaking of electrolyte fluid, doesn't mean the cap isn't going bad.

There's really no way to know without desoldering it and testing it out of circuit

or using a special kind of meter.

Edited by Shplad, 21 March 2021 - 01:34 PM.

Is there any likelihood that it could be the CPU instead of the M/B? 

 

Because you are getting no signs of life at all from the PC the MB would have to be bad as well, explanation, it is possible for a CPU to be bad but the CPU cooling fan still spin up when you press the case power on button whereas the CPU cooling fan will not spin up at all if the MB has completely failed.

Shorted both PSUs (24-pin green wire to a black wire) with a paperclip - fans turn

 

Are you referring to the PSUs internal cooling fans, if  yes, being that you tried shorting out the power switch pins on the MB with no joy that goes further towards suggesting that the MB is bad and possibly the 12V ATX circuit for the CPU.

Question, have you tried connecting the CPU fan to another fan header on the MB to see if it spins up.

Have you done the sniff test? If something internally made the loud pop, then there should be a burnt electrical smell still lingering. Don't forget to sniff the monitor too.

Another thing I would do is to disconnect all hard drives, CD drives..... everything including the video card (remove it)(if it has one), leave one memory stick, CPU and fan in.... hook up a different known working monitor to the motherboard, use the PSU that is in spec and try to boot.... if it goes into the BIOS then it's something other than the motherboard, CPU and that one memory stick.

Edited by flabum1017, 22 March 2021 - 04:12 PM.

Good advice. Sometimes, but not always, you'll smell a burning smell.

If you can't get it to work, what PhillPower2 recommended is called the "strip-down"

method. That helps eliminate extra factors like external peripherals etcetera so

you just have the bare amount of equipment connected that's necessary to boot

a PC.

Good advice. Sometimes, but not always, you'll smell a burning smell.

 

If you can't get it to work, what PhillPower2 recommended is called the "strip-down"

method. That helps eliminate extra factors like external peripherals etcetera so

you just have the bare amount of equipment connected that's necessary to boot

a PC.

I once had a floppy drive preventing a computer from booting..............