Faulty Motherboard

Please see above post.

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M.Joshi
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M.Joshi
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Hi,

A few days ago, our computer suddenly started to emit black smoke and stopped working.

Upon further inspection, the power supply had a large hole blown through the case which seemed as though something had exploded and a black 'gunky' substance leaking from it.

We replaced the power supply and tried testing the motherboard but only the fans power up. I have checked that both power connectors are connected and also tried removing all peripherals and cards.

Nothing appears on the screen and the motherboard does not even get as far as the P.O.S.T?

Looking at the electrolytic capacitors near the P4 power connector, a few of them seem 'puffed up' at the top, with a powder substance leaking from the top.

I tested the capacitors with the continuity setting on a multi-meter and two of them showed as a short circuit. I know testing in circuit will not give a conclusive reading so I will de-solder just to make sure first.

I am wondering whether the short-circuited capacitor(s) on the motherboard near the P4 connector caused the power supply to become damaged?

Does the P4 power supply affect the motherboard's startup routine?

I thought the BIOS would be powered from the main power connector and that the P4 power supply is just for the processor?

The motherboard is a Gigabyte P4 Socket 478 GA-8IRML.

I remember reading about Gigabyte having a problem with faulty power supply decoupling capacitors a few years back?

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M.Joshi
Reply to
M.Joshi

Hi, Its possible, try replacing them with ones from a scrap board that test OK.

-A

M.Joshi wrote:

Reply to
testing_h

The capacitors in the power supply exploded, forcing the motherboard capacitors to handle unsmoothed DC.

Yep, they're toast.

They'll all have to be replaced, forget about testing them. There should be a few capacitors in parallel to give an overall large value. If one in the 'row' has burst or domed on top then you'll have to change all of the paralleled caps. There's no guarantee this will fix the motherboard though, there may have been overvoltage which may have destroyed a lot of components, possibly including the CPU.

Good luck getting those capacitors out- it isn't easy without really good tools like a very hot temperature controlled iron!

Incidentally, reading a short could be normal- the motherboard draws a *lot* of current and the supply rail will have a very low impednace.

More likely the other way round. It's possible though that there was a catastrophic failure on the motherboard, eg a shorted CPU, which caused the power supply to blow.

P4 power supply? You lost me. If you mean the extra connectors and not the main ATX power connector. They're all tied together in the power supply unit itself, they don't come from a seperate.circuit IIRC.

And others as well. It wouldn't likely cause your power supply to blow up though, it would just cause very erratic performance and crashing.

Dave

Reply to
Dave D

The capacitors being shorted will definitely prevent the board from working, you could try replacing them but the only boards I've seen which have had the power supply blow up like that were toast, they had other bad components.

Reply to
James Sweet

Just replace the caps that are blown or have "Rubycon" written on it.

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mistermaniac
Reply to
mistermaniac

Hi,

Thanks for all your useful suggestions.

All the parts including the CPU have been tested separately on different computers and they all seem to work.

I did try to de-solder one of the capacitors (GSC brand) that was puffed up but it was really difficult using an Antex soldering iron and doing so seemed to damage the tiny PCB tracks.

Incidently, the capacitors that were puffed up were around the P4 power connector (Additional power for the processor).

I figured that maybe a short on the motherboard caused the power supply to overheat and one of the capacitors to blow hence delivering a high ripple voltage to the motherboard and possibly damaging various components?

I think we will just purchase another P4 Skt. 478 motherboard - they are fairly cheap on Ebay!

Any brands/models to avoid?

Thanks.

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M.Joshi
Reply to
M.Joshi

Hope this is not a repeat of another post - have a look at this site - lots of info on how to remove and install, identify bad caps, etc.

formatting link

Wayne

Reply to
Wayne

I use a 50W temp controlled station and even that doesn't make the job easy. If you've damaged tracks forget about repairing it.

A wise move. You'll likely have no luck with your old one.

Not really, even the very cheap ones have given me good results. If you see one you like, try and find some reviews before buying.

Dave

Reply to
Dave D

"M.Joshi" bravely wrote to "All" (19 Feb 06 23:05:10) --- on the heady topic of "Re: Faulty Motherboard"

M.> From: M.Joshi M.> Xref: core-easynews sci.electronics.repair:358750

M.> Hi,

M.> Thanks for all your useful suggestions.

M.> All the parts including the CPU have been tested separately on M.> different computers and they all seem to work.

M.> I did try to de-solder one of the capacitors (GSC brand) that was M.> puffed up but it was really difficult using an Antex soldering iron M.> and doing so seemed to damage the tiny PCB tracks.

M.> Incidently, the capacitors that were puffed up were around the P4 M.> power connector (Additional power for the processor).

M.> I figured that maybe a short on the motherboard caused the power M.> supply to overheat and one of the capacitors to blow hence delivering a M.> high ripple voltage to the motherboard and possibly damaging various M.> components?

M.> I think we will just purchase another P4 Skt. 478 motherboard - they M.> are fairly cheap on Ebay!

M.> Any brands/models to avoid?

M.> Thanks.

M.Joshi,

The proper technique for removing electrolytic caps from a multi-layer PCboard is to snip the cap body itself close to the base, pull off the remainder, and then desolder the remaining pins 1 at a time. Trying to unsolder the cap all at once is likely to cause track damage, as you may have already noticed.

A*s*i*m*o*v

... That was a fascinating period of time for electronics

Reply to
Asimov

I once tried to removed bad caps from a motherboard and couldn't desolder the pins. It was as if the leaked electrolyte had chemically welded the pins to the motherboard.

Reply to
AZ Nomad

I've had reasonable luck heating the pins one at a time while rocking the cap side to side to free them. YMMV of course, but that worked for me.

Reply to
James Sweet

It may very well have corroded them together. I suspect what happens is the electrolyte corrodes the solder and changes its properties, increasing the melting point, I've noticed similar behavior with battery leakage on circuit boards.

Reply to
James Sweet

Most of the time the capacitors are soldered really close to the PCB so you cannot reach just under the can to cut the pins?

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M.Joshi
Reply to
M.Joshi

Now that I think about it, I also had trouble getting solder to flow into the connections. It was as if I was using solder without any flux. The solder just beaded off.

Reply to
AZ Nomad

At about the time of 2/19/2006 5:28 AM, M.Joshi stated the following:

Through the sheet metal case?

Yikes.

Dead board. Better to replace it and HOPE the CPU didn't fry.

How old is this computer?

Uh..Yeah... The P4 power supply powers the CPU.

You are wrong. The BIOS is a ROM chip that has the computer's bootstrap code in it. It is executed by the CPU. If any *ONE* of these (Power, CPU, CPU Support, Clock, Chipset, Bus, BIOS, etc...) is blown out or not functioning, then your computer will not boot.

For example: I have a computer motherboard where the USB controller marked it's passing with a whole lotta smoke. Scorched the board in fact. Because I don't use the USB on that machine, it continues to function because it is not a critical part. IOW, the computer can function without it.

As the story goes...

A few years ago, a couple of people from some manufacturer in China left the company and took with them the formula for a water based electrolyte for the capacitors. They then turned around and sold the formula to various other parts manufacturing companies in China, Tiwain, Hong Kong, South Korea, etc... The problem is that they only got part of the formula. As a result, the electrolyte was unstable and would degrade rapidly at elevated temperatures before the caps blew out. You would get something like 250-500 hours or so out of it before you had a problem. Because MY computer uses a motherboard from that era, I check mine periodically. There is a website that details all this.

Unless you are good with a soldering iron, It's best to replace the board. They are not that expensive these days.

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Daniel Rudy

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Reply to
Daniel Rudy

That's what I do. Also, applying some fresh solder will help conduct more heat to the connection. The thick power and ground traces to the caps conduct the heat away very quickly. A temperature controlled soldering iron is a must (the more powerful the better).

This motherboard sounds like a goner to me. They are rarely repairable when they fail to post. I doubt the caps are shorted. If they were shorted, the power supply would shut down. A very large capacitance can look like a short to a DMM continuity test. Andy Cuffe

snipped-for-privacy@gmail.com

Reply to
Andy Cuffe

When testing the capacitors with a DMM continuity test off the board, they did read as a short until they discharged and then the same with the opposite polarity i.e the probe leads switched.

We managed to test the other critical components in other computers (CPU, Graphics card) and luckily they work fine, so it looks like a new motherboard!

Haven't been able to test the RAM though? Hopefully it should be O.K?

On a separate note, the existing RAM is of the 266 variety. Will this work on new boards with DDR400 RAM?

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M.Joshi
Reply to
M.Joshi

"M.Joshi" bravely wrote to "All" (20 Feb 06 18:37:07) --- on the heady topic of "Re: Faulty Motherboard"

M.> From: M.Joshi M.> Xref: core-easynews sci.electronics.repair:358797

M.> Most of the time the capacitors are soldered really close to the PCB M.> so you cannot reach just under the can to cut the pins?

M.Joshi,

Don't try to get under the can. Snip the can itself. It is cheaper, faster to replace a cap than to try salvaging it, and risk damaging the PCB. Caps cost what, $1? A PCB costs what, $50? Your time costs?

A*s*i*m*o*v

... Who's got the Thermonuclear Welding Set? - ToddS

Reply to
Asimov

A.K.A. Rubycon

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mistermaniac
Reply to
mistermaniac

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