short circuit via USB port: what has died?

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#1
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Hi All,

While tampering with an Atmega, I had an accident with the wires hanging around, and I shorted the USB port on my computer.(The Atmega was connected to the computer via a USB-serial converter.) As a result, the computer no longer works. I can switch it on, and the power on LED comes to life, but then nothing happens, it does not reach the boot section. Which one is the most likely component to have died? The motherboard? Is it possible that I can fix the computer by replacing the motherboard?
By the way, isn't the USB port supposed to have a current limiter? At least, in the specifications, there are two current values, 100 mA, and 500 mA, and as far as I know, the USB port should be prepared for these contingencies, and be able to shut the port, if something happens there.
Cheers,
Zoltán

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You know that there are hundreds, if not thousands (on older PCs), of components on a motherboard. So claiming "the motherboard died" is always a good bet when a computer doesn't work. However, that doesn't help much, because of the many components ...

You need to have luck to fix this. You could check the power supply to the motherboard, if all the various voltages are present. Then you could have a look at the area around the USB port if anything is burned there, and remove it (hoping that this removes some short).

If you have a reliable, skilled computer repair shop in your area take it to them instead.

As for USB ports having current limits, well the standard says so. However, because of greed and economic reasons manufacturers do as they please. And don't forget that users like to overload USB interfaces (e.g. by operating power-hungry disks on a single port). So manufacturers partly had to give up limiting at 500 mA, otherwise their boards were returned as "broken".

Stealing Proteus doesn't make you an engineer.

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As the motherboard should have had protection against this, at least now you know which brand NOT to buy next time.

/Jesper
http://www.yampp.com
The quick black AVR jumped over the lazy PIC.
What boots up, must come down.

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The most likely part to have blown first is one of these:

-Processor
-Memory
-Chipset

If you start it up, but you see no POST on screen, and you hear no beep codes signifying error, it's most likely the chipset that went off. Do not lose time and money trying to fix it, buy a new motherboard.

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Next time connect it through a $5 powered USB hub, so that the hub blows instead...

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hugoboss wrote:

If you start it up, but you see no POST on screen, and you hear no beep codes signifying error, it's most likely the chipset that went off. Do not lose time and money trying to fix it, buy a new motherboard.

There is absolutely nothing after switch-on: only the fan runs for a couple of seconds, but then winds down. And you are right, I didn't even think of fixing it myself, I wanted to buy a complete motherboard. I just wanted to make sure that it makes some sense. Am I correct, that we can rule out a processor and memory failure, based on the fact that the BIOS is not loaded? To be more precise, can we say that the motherboard is certainly bust?
Cheers,
Zoltán

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I would also check the voltages from the power-supply.

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jesper wrote:
As the motherboard should have had protection against this, at least now you know which brand NOT to buy next time.

Yeah, you are right, and the more I think of it, the more baffled I get: after all, it is not unconceivable that a device hanging on the USB port fails for whatever reason, and that shouldn't bring down the whole computer.
What is somewhat stupid here is that at the time, I bought this particular model, because it had 4 USB ports. When the incident happened, I used 3 of these: one for the programmer, one as the serial port, and one for the mouse. Sometimes I had something else hooked up to it, so all 4 were needed. It was a Dell Inspiron 1525, by the way.
Zoltán

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ossi wrote:
I would also check the voltages from the power-supply.

It doesn't work with the batteries either. I don't think it is the power supply that failed. Besides, I have opened the computer, and it is really not clear where I should measure what potential.
Zoltán

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ArnoldB wrote:

You need to have luck to fix this. You could check the power supply to the motherboard, if all the various voltages are present. Then you could have a look at the area around the USB port if anything is burned there, and remove it (hoping that this removes some short).

I could remove the USB ports altogether, but that didn't help. And I haven't seen any obvious damage to any of the components; it must be something subtle.

Quote:

As for USB ports having current limits, well the standard says so. However, because of greed and economic reasons manufacturers do as they please. And don't forget that users like to overload USB interfaces (e.g. by operating power-hungry disks on a single port). So manufacturers partly had to give up limiting at 500 mA, otherwise their boards were returned as "broken".

I see your point here, but this is really stupid. All kinds of things might happen to a port, and there should be some mechanism protecting against them. And I am not talking about someone deliberately connecting a shorted development board to the computer, but just accidentally knocking a pair of scissors or a paper clip against the port. But as you pointed out, we can't really change this.
Cheers,
Zoltán

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Keep in mind that Dell power supply connectors are NOT electrically compatible with the ATX standard. Look up the differences.

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If you have opened the case and you see the motherboard check for any SMD fuses blown.Mainly are located around the regulators.

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Quote:
It doesn't work with the batteries either.

Is this a desktop or laptop?

I agree with Ossi, check the power supply first.

If this is a desktop then pull all of the cards you can: Modem, secondary video card, sound card, extra ATA/SCSI/USB etc ports cards. Minimize the system.

Unplug the CD, FDD, additional HDDs except the boot drive.

Do the obvious, check that the memory is well seated, connectors are well seated. This should not be the cause in your case, but you don't want to miss the common / obvious causes.

Try also with ALL of the HDDS, CDs, FDDs, etc disconnected. This changes the BIOS's start up path / sequence.

Before you think of buying a new MB try your current HDD on another computer. You want to make sure it is still accessible, and your files are there. If the failure took out the MB AND your HDD, then trash the unit and get a new one.

Not worth checking the memory, too many kinds out there, and not easily done unless you have special hardware.

IIRC most of the PC power supplies still have a Power Good signal that inhibits the entire power supply. A key place to start looking IF you want to do some board level checking, after you check the rest of the power supplies.

Sorry to hear about the problem... I've had numerous computers die for various reasons over the years. Not a fun experience.

If it is a laptop then you need to call tech support and get past the first layer of tech support. Some brands have "secret" reset codes. In the old days laptops had recessed reset push button switches, but they haven't been used for quite some time. A simple pull of the battery for 15 minutes isn't the same thing.

Good luck.

JC

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DocJC wrote:

Is this a desktop or laptop?

Laptop.

DocJC wrote:

Before you think of buying a new MB try your current HDD on another computer. You want to make sure it is still accessible, and your files are there.

I have already backed up everything from the hard drive. That seems to have survived the incident unscathed. I am quite sure that it wasn't running when this happened, and I went through it with a disk checking utility. There were no problems whatsoever.

DocJC wrote:

If it is a laptop then you need to call tech support and get past the first layer of tech support.

Unfortunately, I am not in the warranty period any more. I had some problem before, and when I called them, the first question they asked was the quick code, which I gave, and then they announced that the warranty has expired, and hung up. I won't even try it this time, because it takes about an hour till you get to a human.

DocJC wrote:
A simple pull of the battery for 15 minutes isn't the same thing.

Oh, is it then possible to reset the BIOS, or whatever, just by removing the cell battery? I haven't thought of that, but I can try.
Cheers,
Zoltán

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Hello... I'm terribly sorry that I'm resurrecting a forum from 7 years ago, but I've run into a similar situation as well.  I'm guessing the OP was able to fix with with a bios reset?

Last Edited: Mon. Jun 19, 2017 - 08:38 PM