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Help! Loud pop sound, possible mobo failure?

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January 13, 2010 7:02:24 PM

Hey, yesterday I built a new computer with an Asus P7P55D mobo, Antec CP-850 PSU, Core i5-750, and Radeon HD 5770.

1) When I plugged everything in, the computer 'clicked', and the power LED, graphics card LED, and PSU fan turned on for a millisecond and then turned off, subsequent attempts to turn on resulted in nothing until I turned the PSU off and then back on.
2) Checked ALL connections and re-plugged in things carefully, then repeated step 1 (same result).
3) I plugged in the CP-850 PSU to another computer: it worked!
4) I plugged in a crappy budget PSU to the new computer, the computer turned on and I heard a loud POP sound followed by a slight electrical/burning smell. The computer remained on but in my panic I turned it off.
5) I plugged in the Antec CP-850 back into the new build to be sure of things, and of course, the initial problem was there.

My theory: the motherboard is defective and the Antec CP-850 has some built in protection that won't power a defective board. The old PSU didn't have so this so it made something pop. This could be completely wrong though. Should I RMA the motherboard? Note: The standby power LED works.

Thank you so much for your help, I'll be sure to return the favour by helping out on these boards.
January 13, 2010 7:12:03 PM

Sounds like a short between the mobo and the case...remount the mobo being sure to put a spacer between the standoffs and the mobo. The mobo may have taken a hit, do a visual inspection of the capacitors, voltage regulators, and the mobo in general to determine if it looks like something got fried.
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January 13, 2010 7:23:32 PM

I looked at the mobo and graphics card, all capacitors look fine. Is it possible that the pop came from the old PSU? I forgot to mention that the old PSU was very, very shitty dusty and old, and had heating problems in the old build.
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January 13, 2010 7:25:47 PM

+1^ - also make sure you did not drop a screw or something else between the MOBO and case tray that might be shorting it out. - you are using all of the standoffs to hold the MOBO above the case correct ? - they need to all be used to keep the board from warping\bending from the weight of the expansion cards to keep space between the soldered connections on the bottom of the MOBO and the metal of the case !

EDIT : was the burned smell coming from the PSU or your case ? - since you said it remained turned on the chances it was the PSU are slim (usually a pop from the PSU will shut down the power)
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a b B Homebuilt system
January 13, 2010 7:40:24 PM

NShukla said:

...
My theory: the motherboard is defective and the Antec CP-850 has some built in protection that won't power a defective board. The old PSU didn't have so this so it made something pop. This could be completely wrong though. Should I RMA the motherboard? Note: The standby power LED works.
...


Either defective, or shorted in the manner described by subsequent posters. Yes, the Antec could have protected itself, but R.I.P. to another fecal PSU.

Remove the mobo and breadboard your system outside of the case, to avoid any possibility of shorts with the case. Don't connect any drives either; they're not needed to POST, and it is possible the short could have been in one of them too.
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January 13, 2010 8:16:01 PM

UPDATE: Wow okay guys turns out the graphics card needed to be re-seated, even though I had already re-seated it before. I was assuming that the mobo would start up and the graphics card not work, but the graphics card actually demands power before the computer will even start at all! Thanks for all the help, but I'm still concerned about that popping sound and what it might have been. All the capacitors I checked seem fine? Is there a possibility that nothing was damaged?
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a b B Homebuilt system
January 13, 2010 8:17:43 PM

Most of the time when you hear a pop it means the PSU has blown up. It's possible you got lucky and that POS PSU didn't damage any other parts in its blaze of glory.
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January 13, 2010 9:09:56 PM

Another update: Okay the graphics card thing was NOT the problem. I had actually plugged in a connection labeled P4 from my power supply into a fan controller, thinking it was a fan. The power supply probably saw something wrong with that and shut down.

Still doesn't explain the pop though. I only plugged in the 24 pin and 4 pin connections with the old power supply. Maybe the PSU popped for a different reason.

So if I don't see any damaged capacitors, does that mean things are fine? Is there any way to diagnose the mobo?
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January 13, 2010 9:30:35 PM

if it has a safety shut off, it might of been that you heard popping, like a circuit beaker in your house when they go it pops. had to shut off the PSU and on again to reset it.
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a b B Homebuilt system
January 13, 2010 10:32:48 PM

A loud "pop" followed by an electrical / burning smell is NOT a circuit breaker. Something croaked. If it was an ancient capacitor, the PSU may still turn on, but its filtering would be even worse. An old jonnyguru review looked at some cheap PSUs, including an old one with at least one bad capacitor. The scope shots of the ripple were really scary.
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Best solution

a b B Homebuilt system
January 14, 2010 12:45:59 PM

Here's a note of hope / optimism. The loud "pop" sound came the first time you hooked up an old PSU that you knew was very dirty inside. Just maybe all that happened was that, as it started up, some of the accumulated dust inside it offered a temporary conduction path that allowed one large spark to make the sound and also to burn off the string of dust involved. From then on, no more arcing, no more noise and smell, and no impact at all on your mobo or the original NEW PSU.
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January 24, 2010 1:41:49 AM

Best answer selected by NShukla.
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a b B Homebuilt system
January 24, 2010 10:01:53 AM

Your "Best Answer" selection does not explain why the CP-850 will not stay on, powering that rig.
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January 24, 2010 3:27:23 PM

No no, the CP-850 works fine, my question switched to why there was a pop when I hooked up the old PSU for a test. Paperdoc's explanation seems to make sense.
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