VGA Cable on fire!

I have just replaced my motherboard (it has on board graphics and audio} and I used all the new cables which came with it - when I turned on the computer the vga cable caught fire - why did it do this? The cables were round the right way - is it a faulty cable or a problem with the motherboard? Luckily the computer still works (without the monitor) and the monitor is ok.
Emma083198Asked:
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tfabianCommented:
my guess is that the problem is with the cable.. return it to your place of purchase and demand a replacement..  especially if you managed to connect the monitor successfully using another cable, which is what I presume you did..



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Emma083198Author Commented:
Edited text of question
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warmcatCommented:
Emma,

Hahahaha!  If this had happened to me I would have crapped myself in horror.

How do you know the monitor is 'okay'?  How do you know the computer still works if you have no monitor attached?

The only way to dump enough current to heat up the conductors in the cable to make smoke come off the insulation involves either a dangerous fault in the monitor itself or a miswired mains plug somewhere.  Replace the mains cables for both the PC and the Monitor.

It is not possible - not possible - for a problem with the VGA
cable itself to generate enough current flow to even make the cable warm, let alone smoke.

Regards,

-Andy
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Emma083198Author Commented:
The monitor works because I now have it plugged into another computer and all is well.  Also the main computer cables are fine because I am also using them with another computer.  I know the computer still works because I plugged in an extra VGA card and everything worked (except for a conflict with the on board graphics and the extra card).
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thommy031498Commented:
Do you have a voltmeter?
Check if the outer shell connector of the VGA socket is on Ground level  or for some reason connected to 5V or 12V

How is the VGA socket connected to the mainboard.
Is it soldered in, or is it connected by a Jumper wire with an connecter that can and has been put in the wrong way round.
Or the connector is wrong connected inside
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thommy031498Commented:
Do you have a voltmeter?
Check if the outer shell connector of the VGA socket is on Ground level  or for some reason connected to 5V or 12V

How is the VGA socket connected to the mainboard.
Is it soldered in, or is it connected by a Jumper wire with an connecter that can and has been put in the wrong way round.
Or the connector is wrong connected inside
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warmcatCommented:
Emma,

I see you say 'onboard graphics'.... is it possible that the motherboard connector for this has been mistaken for a different connector, or, as thommy suggests, reversed?  It's still really very hard to see how enough current could flow to cause the outcome without tripping a fuse or current-limit.

Sorry to bang on about it, but it was the same power cord you used with the monitor both when the cable melted and subsequently?  The same wall socket?

Regards,

-Andy
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Emma083198Author Commented:
Yes same power cord and same wall sock - which I am plugged into right now.  Also it isn't possible to plug the cable in the wrong way around as there is a pin blocked off. - and yes it was the right connector.
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Emma083198Author Commented:
The VGA ribbon cable is connected by a plug, which plugs straight into the motherboard.
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mazziniCommented:
If the monitor and the CPU were connected to different outlets, verify if one of the outlets has an inverted connection, e.g., the "live" wire in place of neutral, and vice-versa, or even the ground and "live" wires in the wrong place. The correct assignment is: looking the wall outlet with the ground pin down, the left pin is the neutral wire, and the right pin is the "live" wire:
                  neutral ->    |        |    <- "live"
 
                                       O        <- ground


Regards,
mazzini
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vanoverCommented:
If everything but the cable is okay after this freaky event, the cable was probably the culprit. Here are two more possibilities for you to digest:

1.  You said the vga cable caught fire when you turned the computer on.  Was it immediate or after a while?  If immediately, the problem could've been caused by a short circuit within the vga cable.  The cable may have been crimped bad enough for some wires inside to break & short out.  This situation most likely would have produced a large pop (zap) as soon as you applied power.  However, your motherboard (or some peripherals) should have been fried if that happened.

2.  If it was a while before the cable burned, the problem may have been caused by an overloaded cable (drawing too much current).  The most plausible reason for this to happen is a misaligned cable connection or a broken pin.  This would have produced a gradual warming of the cable & you probably would have smelled it burning before it actually burst into flames.  You may have noticed a degradation in monitor performance, too.

After saying all that, I think it was just a cheap-o cable with a manufacturing defect.  Just count your lucky stars all you lost was a cable.

By the way, I'd keep a fire extinguisher handy from now on, just in case...
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warmcatCommented:
vanover,

The only problem with both of the suggestions is that there is no way any of the drivers on to the cable would survive passing enough current to even noticably warm any of the conductors.  The driver would crack open and die first.  This includes scenarios of shorting any or all of the conductors in the cable together, or any or all of the conductors being opens.  Even if your video DAC featured supercooled God-buffers capable of powering small cities, the PCB tracks passing the current between the DAC chip and the connector would blacken, curl up and break before a length of wire passing the same would noticeably warm.

The only way I can see for the symptom to be provoked involves the monitor chassis being at a different potential than the PC chassis, and in fact the shield braid in the cable was getting hot as it tried to marry the two grounds.

That's why I originally suggested a dangerous fault in the monitor (ie, live chassis in the monitor) or a wiring fault in the mains lead (ie, earth pin connected to live).

Regards,

-Andy
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warmcatCommented:
Doh!

Now I trouble myself to look up the VESA DDC pinout I discover there is a 5VDC line powered from the PC.  If this was not fused at the motherboard, and there was a short at the monitor end of the cable from the 5V line to GND, then this would explain why your cable smoked.

With this in mind it could well have been a one-off fault with the cable.

Interestingly, all modern motherboards use a self-resetting fuse on the _keyboard_ 5V line: I'm surprised there was no such fuse or current-limiting on the videocard for this supply line.

Regards,

-Andy
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mlaiosaCommented:
Im unclear, is it the cable from the compter to the monitor or the monitor's power cable that caught fire?
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Emma083198Author Commented:
neither - it's the ribbon cable from the motherboard (on board graphics) to the back of the computer (attached to the other end of cable are the sockets which stick out the back.
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warmcatCommented:
If the ribbon cable was cut with a blunt edge, it can sometimes create shorts across the exposed ends.
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RoadWarriorCommented:
What monitor is it? I suspect an ibm ps/2 model. if not, another early vga. would be surprised if it is a modern svga. If it is, I can tell you why it happened, but unless you are into wiring up your own patch leads. not how to solve it.
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