Crack & Stink Gigabyte GA7N400 Pro 2

[socketa]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

thanks
spent a couple of hours searching, to no avail

so a dud cap would be very unlikely to have caused this?

there is a short to ground (6.2ohm) on the mobo 3v rail
but perhaps that could have being caused by over-voltage from the psu.

not going to fix this psu, but would like to have some rough idea as to what caused this

have probably snapped the legs of a couple of components as i was moving them

... so the pics are probably not necessary, but have included them anyway

[Agent24]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

Unfortunately, PC PSUs practically have no schematics available. They are not considered worth repair since they are all interchangeable anyway. There are basic reference designs and of course controller datasheets etc to give some idea but that's about it.

If you know the general layout of a SMPS you can trace what the resistor connects to and find out (probably) what it's for, otherwise, it would be tricky if you don't.

Post photos of the whole PSU to show resistor location relative to everything else, and also top down, and a bottom side photo of the tracks including which pads are the resistors and we might be able to help figure it out.

Resistors usually burn when something they supply power to is shorted, or they see an overvoltage condition.

[socketa]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

just found the culprit that made the stink (and possibly the crack)
am guessing it was caused by one or two bad caps (photo in previous post) stressing the resistor out?
it was well hidden under a choke, and behind a cap

now am trying to locate a circuit diagram for an ISO-450PP 4S to work out: if one of these 4 caps failed, which one would lead to the overheating of the resistor.

in hindsight, after being quite ignorant when it comes to this stuff, have learned a few lessens
don't assume a psu is good just because the psu case looks clean and tidy
don't assume that the smell is coming from the mobo
and as a consequence of this ignorance, and help from here, now have a few clues as to what's what.

[momaka]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

That ISO-450PP 4S is a CWT (Channell Well Technology) PSU.

The ISO series is their budget line and varies in quality anywhere between very decent and plain-straight crap. Usually the crappy ones are bought and re-branded by "fly-by" companies, such as Cyberlink and Turbolink (common gutless wonder PSUs that come with cases), and I think OKIA as well.

The ISO line is based on a very old and inefficient, but also very stable design - the half-bridge. However, the real kicker is that the ISO line use a 2-transistor 5VSB circuit that has a "critical" cap. If the critical cap fails, 5VSB can overshoot very high - sometimes as much as 12V to 13V. USB devices and older motherboards often can't handle this overvoltage, so they fail. The ISO line is known to use crap caps such as Fuhjyyu, so that "if the critical cap fails" always becomes a "when the critical cap fails" - i.e. inevitable disaster unless the PSU is completely recapped pre-emtively.

That said, your PSU may still be salvegable if you are up for "fun" project. If it's decently made (crap-caps aside), a recap with high-quality caps can make it work like new again and actually last for many years.

[shovenose]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

And that would be why really cheap generic power supplies should never ever under any circumstances be used, purchased or sold. (at least not without being recapped and modified)

Unfortunately they work just fine long enough for most people, so they don't know or care.

[Sparkey55]

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

I once had a Epox 8rda+pro NF2 get hit by a lightning strike from about 30 feet away, Ethernet cable plugged in, no power cable connected. The board still work well but the onboard nic chip was fried brown colered in the center and could not hold a finger on it for more than 2 seconds.

[Agent24]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

There are many PSU manufacturers with bad reputations - on this forum.

The problem is most people don't know how crap some of them can be, it helps that often they upgrade them before they fail anyway.

Even if enough of them died to make everyone know how bad they were, the OEM would just relabel it next month - like the way the brand names on the stickers seem to change every couple of years anyway...

[socketa]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

ISO-450PP 4S

Yes, i now know that it is a hunk of junk

Prior to this, had seen quite a few of them, and thought that they must be OK, otherwise the manufacturer would get a bad reputation and no one would by their products, and their business would collapse.

But since i had no idea, i guess that neither would many others, and it would be too much of a hassle for some to find out what happened, and they would just throw the PC in the rubbish bin, and then buy another time bomb.

[c_hegge]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

And that would be why really cheap generic power supplies should never ever under any circumstances be used, purchased or sold. (at least not without being recapped and modified)

[Agent24]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

It's not uncommon for cheap PSUs to turn nasty and kill boards, actually. The cheap ones also have a lack of decent protection for anything they are powering or themselves, too.

The crack was probably the southbridge going up in smoke, but could have been one of the capacitors. Possibly your PSU had a faulty 5vSB regulator circuit sending too high a voltage into the motherboard. Or there is some regulation problem on the main rails, maybe even a totally shorted rectifier allowing AC out into the motherboard.

What brand and model is the PSU?

[socketa]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

update:
re-tested the psu and it started to smoke
so, looks like the crack sound, and the odor, was the caps blowing their vents?
didn't know that a psu could destroy a mobo, and assumed that they would all have over-current protection as a basic feature.
this is the first time that i've ever seen a psu die (and unfortunately, also "take-out" a mobo with it).

here is the pic of the caps:
two are domed, and the other two (teapo) have opened up

[socketa]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

thanks all

[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.

[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.

[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!

[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.

[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

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.

[goontron]

Re: Crack & Stink Gigabyte GA7N400 Pro 2

yep, its buggered!

[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