Crack & Stink Gigabyte GA7N400 Pro 2

[socketa]

Fired up a (Gigabyte GA7N400 Pro 2) motherboard that i had in storage, that was previously running OK
Board on bench with good ram and psu, with just the power and power LED connectors connected and a stick of ram.
Pushed power button fans started to spin then a couple of seconds later heard a crack sound (like the sound of a whip cracking) and then the smell of something that has burned, coming from the board.
After searching for a couple of hours, with a strong light and magnifying glass, i couldn't see any sign of burned components, bulged or leaking caps.
It wouldn't turn back on (even using a jumper across the 2 motherboard power-on pins), so i removed the connectors and 'paper-clipped' the earth and start terminals on the power connector, to get it going.
Noticed the RAM LED on the board lighting up and then another 'crack' sound, so immediately stopped the psu.

Since i couldn't find any noticeably burned-out components, i removed the CPU and the north-bridge, and didn't find any signs of damage there.

So checked voltage on the motherboard power pins - 4.1v
The south-bridge gets hot to touch - so power is getting to that

Removed the 6.3v caps - they look OK, and charge up/discharge similarly

What component, other than exploding caps, can make this crack sound, and burning smell with no visible signs?
What would be stopping a jumper across the motherboard power-on pins, from activating the psu?

TIA

[selldoor]

Re: Crack & Stink

pictures top and bottom - what surface are you working on.

[socketa]

Re: Crack & Stink

Hi,

Working on cardboard
Photos here http://www.stillflowing.comze.com/gigabyte.htm
(Have put the 3 X 6.3v caps back in - the 3 at the bottom of the heatsink)

And have tried again with new ram/different slots/no ram,
still now power-up
you can see the green jumper on the top RHS, the placement of, which fails to activate the psu

[pfrcom]

Re: Crack & Stink

The south-bridge gets hot to touch

If it gets -too- hot to touch, usually means a deceased motherboard in my experience

[Agent24]

Re: Crack & Stink

With a noise and smell, something has definitely blown. Might have blown out the bottom where you can't see it though. Something like the VRM controller IC(s) perhaps.

You could try checking all the MOSFETs for shorts.

Also, please post photos on the forum for future visitors.

[stj]

Re: Crack & Stink

take the cpu out and look to see if it has surface-mount poly's under it.

[socketa]

Re: Crack & Stink

Hi,
Did that already (in post #1)
All the polys look good, thanks

Have gone over the board several times, thoroughly, with a magnifying glass and see no signs of burned components or shorted/damaged traces

Found this thread:
https://www.badcaps.net/forum/showth...&highlight=462

But, unfortunately, it went nowhere, unresolved, and ended with someone giving up and buying another motherboard (as so many of these discussions, on the internet, do)
However, (and consequently), i see that the first thing to do (after a thorough visual inspection), is to test the pins that the psu plugs into.
I think that a systematic approach is better than unnecessarily de-soldering mosfets at random, and and testing them

So the first step is to do a power-pin test
And now i see that there is a short on the main 3.3v rail (all 3 pins are shorted to earth).
The other pins test open circuit, after (what looks like) some initial current to capacitors.

Am thinking (but not sure) that maybe it isn't the input/output mosfets - because the psu fan spins, and the southbridge heats up, when the psu is jump-started.

What would be the next logical/sensible step in testing?

Seems that there is some faulty, burned-out, shorted-to-earth, component in between the power button switch terminals and the power supply, that is preventing mobo from being switched on.

As requested, here is a photo of the motherboard

[Agent24]

Re: Crack & Stink

I think that a systematic approach is better than unnecessarily de-soldering mosfets at random, and and testing them

You don't need to desolder them to test them for shorts. If they are shorted, they will show as shorted on and off board.

[c_hegge]

Re: Crack & Stink

Is it just me, or does the southbridge look slightly brown on top?

If you're only running the board for a few minutes, then the southbridge should hardly feel warm. If it's getting too hot to touch, then it's cooked.

[Topcat]

Re: Crack & Stink

the southbridge has defintely been hot.....but that's not uncommon for a nforce chip.....but its definitely scorched.

The fet circled in this image appears to be cracked....but it was hard to tell from the low res photo.

[socketa]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

Appreciate you guys (which, of course, may include non-male guys) taking a look at this.
That fet is not cracked,
i think you might be looking at the shadow.
Also note that the photo didn't show the short middle drain pin (but it's there).

However, then had a look at the south-bridge
Rubbed finger across it and felt a very fine ridge on it's surface.
At first, thought it was the printing on the surface, but upon closer inspection there is, what appears to be, the tiniest little crack in it.

Previously didn't get spend too much time over it, thinking that the south-bridge controlled the peripheral ports - not the on/off switch that starts up the PSU

So is that a good sign that it's knackered?
Can i test it with a meter?
Can a such noticeable odor, come through such a miniscule crack?

Also tested the big mosfets, 3 of them had shorts, from drain to earth and from source to drain.
All 6 of them had shorts from source to earth
So are these last 3 OK because they don't have shorts from drain to sink and perhaps have their sources connected directly to earth?

For the sake of completeness, here is the visual of the suspected crack, that might have resulted from the audible crack - it's between the V and the I

[c_hegge]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

That southbridge is well and truly cooked (and yes, that crack is all it takes to let out the magic smoke and give off that burned electronics smell). I'm afraid your board is cactus.

Just for future reference, we prefer images to be attached locally, rather than using 3rd party image hosting

[goontron]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

yep, its buggered!

[Agent24]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

So is that a good sign that it's knackered?
Can i test it with a meter?
Can a such noticeable odor, come through such a miniscule crack?

Yes, it's blown, unfortunately. There is no test you could do that would tell you anything you don't already know. The only thing you could do is replace the chip (not worth the time and expense, unless you are rich and want to do it for 'fun')

And yes, burnt silicon always has that strong smell. You'll never miss it if you ever smell it again!

Also tested the big mosfets, 3 of them had shorts, from drain to earth and from source to drain.
All 6 of them had shorts from source to earth
So are these last 3 OK because they don't have shorts from drain to sink and perhaps have their sources connected directly to earth?

In general the VRM circuits have at least two MOSFETs (some have extra in parallel) in a totem-pole configuration, and the lower one has its source connected to ground, so that is normal - plus the other MOSFET would have its source connected to ground through the shorted one below it.

[socketa]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

Thanks,
That took up two whole days.
Have got some spare parts now.
And seeing that the board came with a big copper heatsink and athlon xp3000, it might have being a gamer computer, and possibly, overclocked - would've that helped to cook the chip?

Bought it second hand, and had it lying around for a few months.
Turned it on, and a few seconds later, it went "crack", and the fans stopped.

(Just noticed that i used "sink" instead of "source" in the previous post.)

How do i upload images locally?
i checked the link properties of the last pic, on this thread, of the south-bridge - it appears to be local because the address is: https://www.badcaps.net/forum/attach...3&d=1404195288
If not, then i'm happy to give it another go.

[Agent24]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

I suppose it's possible that overclocking and overheating resulted in early failure of the chip, but as for the thing burning out completely, I don't know.

This FAQ here: https://www.badcaps.net/forum/showthread.php?t=1868 shows you how to attach\upload images.

[stj]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

in my experience,
unless you buy a server class board from someone like tyan,
the chips either need heatsinks that arent fitted, or the heatsinks are too small.

every board i get, i run for a few min and then do the finger-test.
i usually end up changing sinks or finding some way to mount a decent fan on them.

this especially goes for some of the newer intel chipsets - those bitches generate more heat than the cpu!

[kc8adu]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

bad power supplies with +5stby overshoot and static/bad devices on usb caused most of those nvidia chip failures.

[Topcat]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

Yup, you let the holy smoke out of the SB chip. its quite clear in that second pic.

[socketa]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

thanks all