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Can a different Ohm rating resistor burn a pc motherboard?

  1. May 15, 2015 #1
    Hello, my motherboard recently has stopped working, so I returned it to warrany, they fixed it, but after a few months the board broke again, but unfortunatly the warranty has ran out, so I'm attempting to fix it myself in the freetime :D So I have found a resistor on the motherboard, that looks like it has been replaced, because there are markings of not cleaned flux near it. I couldnt see the numbers on it because it looks like it has been burn, so I cant identify what Ohm rating the resistor is, because when I attempted to clean it, the black covering went off. I have measured the ohms using a multimeter before I cleaned or even touched it, and it was around 350 Ohms, after cleaning it has increased. Im thinking that the resistor ohm rating should have increased when it burned, so I suppose that the resistor rating should not have been more than 350 Ohms. Most of the resistors I've found on similar places of the board (Near IC power controllers) are either somewhere around 2.2 Ohms (2R2) or 0 Ohms. Should I try using a 2.2 Ohm resistor, or can it destroy the motherboard completly? Or should I try using a higher Ohm rating resistor (Something like 3 Ohms), but I havent found a single resistor on the board higher than 2.8 Ohms.
     
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  3. May 15, 2015 #2

    mfb

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    Using a multimeter on a component in a circuit can give wrong answers.
    The resistance change of a resistor when burned is not predictable - I saw them going in both directions so far.
    Using a wrong resistance can (does not have to) certainly destroy the board. Can you find a working board of the same type where the label of the resistor is readable?
     
  4. May 15, 2015 #3

    phinds

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    I doubt if you would totally destroy the motherboard with a wrong resistor but you DO run the risk of causing malfuntion and/or other burned out parts. Not a good idea.

    I find it hard to believe that there are 2 ohm resistors on your board. Much more likely is 2K ohms. Since you don't really know this stuff, I'd advise against trying to fix it yourself.
     
  5. May 15, 2015 #4
    Thanks for the quick responses, I think ill try looking for someone with the same motherboard and look up the label. About the not knowing this stuff thing, I don't really care if I don't succeed, because I already have a new motherboard, but this one is a bit better, so if I'll manage to fix it I'll switch them over. :) Its more like a hobby of mine to tinker with stuff
     
  6. May 16, 2015 #5
    Thank you for your advice on looking for the same board. I have found an image of it on the web where I could read what's written on the resistor. I don't know how didn't I think about that in the first place :D I replaced the resistor with the same one (0 Ohms), and the board works just as new now! Thank you very much!
     
  7. May 16, 2015 #6

    phinds

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    0 ohms is just a wire. Is that what you used to replace the resistor?
     
  8. May 16, 2015 #7

    meBigGuy

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    That's pretty scary, that a 0 ohm resistor burnt out. I guess it might have been a bad solder joint that caused it? I've never experienced a burnt 0 ohm resistor. I realize they have current limits, but ... still ....

    I guess I would replace it with a wire and see what burns out next.
     
  9. May 17, 2015 #8
    I agree. Something is drawing too much power.

    Put your finger on nearby parts (when running). See if any are extra hot. Also check your supply voltages. Use a scope and look for transients (or check the AC voltage on the DC source if your voltmeter can do that -- most can. The scope is better if it can catch transients.)
     
  10. May 17, 2015 #9
    No, I replaced it with a new 0 Ohm resistor. I tried to keep the PC on for 2-3 hours, and then checked nearby areas for anything hot, but its all very cool. Should i try keeping it on longer? Before the board stopped working, I was using a really cheap PSU, so when the motherboard died before I plugged in the new one I replaced it with a better one, and threw the old one away, so I can't check its voltages, but the new ones are fine. Could the resistor have fried because of a bad PSU? I guess the safest way would be to wait and see if it fries again with the new PSU, if it will then I guess the only way to fix it will be to short the resistor and wait to see what fries then. I don't want to do it now because the resistor is very close to the south bridge, which controls most of the IO, so I wouldn't want it killing something else in my setup because I suppose the resistor is like a safety (Don't know how the thing is called in English, the thing that protects hardware from current spike) for the other components.
     
  11. May 17, 2015 #10

    phinds

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    Did you not read post #6? Did you not understand it? Why did you not answer it?

    I tell you again, there is no such thing as a "0 ohm resistor". Zero ohms is just a wire so no one is going to actually fabricate a resistor that is zero ohms, since you can just use a wire.
     
  12. May 17, 2015 #11
    Zero ohm "resistors" are common. They are used as jumpers. Sometimes there will be several devices (or versions of the same device) which use the same board with different value resistors, some of which are zero Ohms for some versions.

    While technically they aren't resistors, but jumpers; they look the same and are commonly referred to as resistors.

    There are also fuses which look the same. Perhaps it's a fuse?
     
  13. May 17, 2015 #12

    phinds

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    I never heard of such a thing but I just Googled it and, as you well knew already, you are obviously correct. Thank you for correcting me on that.
     
  14. May 17, 2015 #13

    mfb

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    A bad power supply can deliver voltages that are too high, that can kill some components on the board.
     
  15. May 17, 2015 #14

    meBigGuy

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    As I previously mentioned, It is very possible that a bad solder connection cause high resistance and burnt the board and resistor. I've seen this often in applications with power transistors and power resistors. The component gets hot, eventually crystallizing the solder joint, which increases the resistance, and eventually the board burns (sometimes).

    So, I suppose it is possible the resistor burnt before the board. Do you see signs of heating on the board around the resistor vias? Before you replaced it, was the solder joint dull (like it crystalized) or still shiny?

    It is unlikely (but possible) that the old PSU caused the issue.

    My Best Guess:
    It is possible that the original problem was a bad solder joint, which damaged the resistor. It was then fixed by repairing the solder joint, but not replacing the resistor. The resistor then failed afterwards. Now that you replaced it with a good resistor and good solder joints, all will remain working (we can hope)

    Just guessing, of course.

    You did good, finding the resistor, the value, and replacing it. Not many would bother. I love the feeling of fixing modern electronic devices. People look at me funny when I say I repaired my TV, or whatever.
     
  16. May 18, 2015 #15

    Integral

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    Not correct. We place 0 ohm resistors with regularity. This is how many circuit boards are configured for slightly different applications.
     
  17. May 18, 2015 #16

    phinds

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    Yes. See post #12
     
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