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What happened to this motherboard?

A while back I bought a used 500mhz computer on Ebay. (that was my big mistake). When I got it, it worked well, except for the floppy drive. I contacted the seller immediately and he sent me another floppy drive to replace the bad one. I replaced the drive and turned it on. It worked fine but since I wanted to add another harddrive (as soon as I got one), I left the cover off the case. That turned out to be a good thing, because I was sitting at my desk on the web when I noticed a hot burnt odor. Then I saw smoke. I looked at the computer and saw smoke coming off the motherboard. There are these donut looking things on the board. They look like a white lifesaver candy wound with 20 or 30 loops of a fairly thick enamelled wire (actually not all that thick, probably a 20 gauge). Oddly enough, the computer continued to work the whole time, and I know that because I saved whatever I was typing before I shut off the power. I found all the enamel burned off the wire on that coil and it was black. I was glad the cover was off the case so I could see what was happening.

I carefully looked for anything that might create a short and found nothing. I got my fire estinguisher (just in case), and turned the computer back on. It booted up, and worked fine. I turned it on and off several more times, and it still worked, and I never saw more smoke. The seller would not replace it because it was 2 ot 3 weeks later by then.

What could have caused this? What are those coild called and what is their purpose. It seems there are 2 or 3 of them on all motherboards.

Needless to say, I do not use this computer. I dont trust it. I just took out all the drives, ram, and cards and put them on another motherboard. I know I can use that case again, but question the power supply. I definately will not use the motherboard again, and worry about the CPU.

Anyone have any idea what caused this? I'm just curious more than anything else. I figure the MB is best going into the trash, and I have a faster CPU now too.

Thanks

Plumber

Reply to
plumber1
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Those are probably inductors used to limit noise on the DC power lines. If they overheated, that usually indicates a fault on the motherboard. It takes a great deal of energy to burn those lines, so I would look for a damaged regulator or shorted capacitor on the board. The problem may be a short on one of the inside layers of the board as well, so you may have to remove the board and try to look through it. If one of the layers is a ground plane, you will not be able to see through the board.

- Tim -

Reply to
Tim

Actually the most of the inductors described are not noise filters at all, but part of a switching power supply regulator that converts either 5 or 3.3 volt supplies to lower voltages such as 1.5 volts for the CPU. They often operate at high currents (perhaps as much as 10 - 20 amperes). There are also some boards that have regulators to generate higher voltages for other components on the board such as built in audio or RS232 ports. I have never seen one get hot enough to cause smoke without also something else wrong. My guess is that particular regulator was associated with something other than the main CPU/memory system or else the machine would not run. Do all of the I/O ports, built in peripherals, and add-on cards operate?

David

Reply to
David

New motherboards with CPUs and often CPU fans can be had at retailers such as Frys (they also have a a web) for $80 to $100. I have built many PCs with these: P4s, AMD etc,

Reply to
Dave

Something has shorted on the motherboard, it's not worth trying to repair one so old, but the rest of the components will be fine.

Reply to
James Sweet

Look for the buldging electrolytic capacitors....Paul

Reply to
catguy

Reply to
Jeroni Paul

bad caps.

--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
Reply to
Jamie

This may be educational

formatting link

Personally, I would not have spent a dime for a 500 MHz PC, when Fry's area selling brand new Pentium 4 with software for $ 299 (last year models being replaced by new ones).

gb

Reply to
w9gb

Hi!

If the coil got hot enough to smoke, the voltage may have been held down to a much lower value by virtue of the coil's resistance.

William

Reply to
William R. Walsh

Many many motherboards from that era had bad caps. Did you examine the caps for bulging and/or leaking?

Reply to
AZ Nomad

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