Welcome guest. Before posting on our computer help forum, you must register. Click here it's easy and free.

Author Topic: If a MB dies, is it always worth replacing the PSU as well?  (Read 6498 times)

0 Members and 1 Guest are viewing this topic.

giorgio652

  • Guest
If a MB dies, is it always worth replacing the PSU as well?
« on: March 06, 2008, 03:21:53 AM »
I run a computer repair company, and yesterday was given a piece of advice from a fellow computer professional; which was to always replace the PSU at the same time as replacing a dead motherboard.

Theory being, most MB's die due to the PSU sending unstable voltage so it is fairly likely to happen again, so for the price of an extra £20 you and the customer will have piece of mind.

Can any other professionals comment on this? I'm unsure whether to take it as gospel.

Thanks :)

street1 (RIP)

  • R.I.P.


  • Egghead

  • I Triple Dog Dare You!!! LOL
  • Thanked: 14
    • Obituary
  • Experience: Beginner
  • OS: Windows XP
Re: If a MB dies, is it always worth replacing the PSU as well?
« Reply #1 on: March 06, 2008, 03:59:27 AM »
Based on the unpredictable flow of electricity,that same
theory would hold true to replace the whole computer.
Sorry,The USA has ruined the language The United Kingdom loaned us. We do our best not to type gibberish. I Hope you can forgive us.

homer



    Expert
    Re: If a MB dies, is it always worth replacing the PSU as well?
    « Reply #2 on: March 06, 2008, 11:50:23 AM »
    Based on the unpredictable flow of electricity,that same
    theory would hold true to replace the whole computer.

    the flow of electricity is quite predictable, i believe you meant to say due to the unpredictable voltages.

    personally, i would check the voltages with a voltmeter before simply throwing out the power supply because it might have irregular voltages.

    WillyW



      Specialist
    • Thanked: 29
    • Experience: Experienced
    • OS: Windows XP
    Re: If a MB dies, is it always worth replacing the PSU as well?
    « Reply #3 on: March 06, 2008, 12:15:02 PM »
    ...
    the flow of electricity is quite predictable, i believe you meant to say due to the unpredictable voltages.

    personally, i would check the voltages with a voltmeter before simply throwing out the power supply because it might have irregular voltages.

    The hard part there is -  how do you check the voltage(s) with a proper load?
    If the ps is sketchy,  it could show correct voltage until a load is placed upon it.

    By the way -  here's a question:    Does anyone know for sure if it is ok to switch on a modern ps with absolutely nothing plugged into it as a load?
    .



    squall_01



      Prodigy

      Thanked: 80
      Re: If a MB dies, is it always worth replacing the PSU as well?
      « Reply #4 on: March 06, 2008, 01:32:02 PM »
      Thats not nessaryly true as the board could die from ESD.  How does he really know there bad with out testing them?
      Windows 7 RC Tester.  Working on it.  Your monitor says etchasketch on the side!

      If I fall who is there to pick me up now.  I stand alone but I stand as the gaurdian for whom I wish to protect.  The sound of my blade utters my name as you fall.  For I shall not move.  For those that forsake the very people are wosres

      patio

      • Moderator


      • Genius
      • Maud' Dib
      • Thanked: 1769
        • Yes
      • Experience: Beginner
      • OS: Windows 7
      Re: If a MB dies, is it always worth replacing the PSU as well?
      « Reply #5 on: March 06, 2008, 02:42:14 PM »
      Thats not nessaryly true as the board could die from ESD.  How does he really know there bad with out testing them?
      What does this mean ? ?
      " Anyone who goes to a psychiatrist should have his head examined. "

      homer



        Expert
        Re: If a MB dies, is it always worth replacing the PSU as well?
        « Reply #6 on: March 06, 2008, 02:56:43 PM »
        ...
        the flow of electricity is quite predictable, i believe you meant to say due to the unpredictable voltages.

        personally, i would check the voltages with a voltmeter before simply throwing out the power supply because it might have irregular voltages.

        The hard part there is -  how do you check the voltage(s) with a proper load?
        If the ps is sketchy,  it could show correct voltage until a load is placed upon it.


        the voltage at the supply will stay the same regardless if a load is placed on it or not. the voltage after the load may, however, experience a drop, but that is not the fault of the supply, it is the fault of the load.

        Quote
        By the way -  here's a question:    Does anyone know for sure if it is ok to switch on a modern ps with absolutely nothing plugged into it as a load?

        its ok.

        squall_01



          Prodigy

          Thanked: 80
          Re: If a MB dies, is it always worth replacing the PSU as well?
          « Reply #7 on: March 06, 2008, 04:21:40 PM »
          Thats not nessaryly true as the board could die from ESD.  How does he really know there bad with out testing them?
          What does this mean ? ?

          patio? ESD Electro Static Discharge.  USe an volt meter and see if it works with a load
          Windows 7 RC Tester.  Working on it.  Your monitor says etchasketch on the side!

          If I fall who is there to pick me up now.  I stand alone but I stand as the gaurdian for whom I wish to protect.  The sound of my blade utters my name as you fall.  For I shall not move.  For those that forsake the very people are wosres

          street1 (RIP)

          • R.I.P.


          • Egghead

          • I Triple Dog Dare You!!! LOL
          • Thanked: 14
            • Obituary
          • Experience: Beginner
          • OS: Windows XP
          Re: If a MB dies, is it always worth replacing the PSU as well?
          « Reply #8 on: March 06, 2008, 04:32:58 PM »
          So far ,so fun. I'm always learning folks.
          Sorry,The USA has ruined the language The United Kingdom loaned us. We do our best not to type gibberish. I Hope you can forgive us.

          WillyW



            Specialist
          • Thanked: 29
          • Experience: Experienced
          • OS: Windows XP
          Re: If a MB dies, is it always worth replacing the PSU as well?
          « Reply #9 on: March 06, 2008, 04:50:09 PM »
          ...
          the voltage at the supply will stay the same regardless if a load is placed on it or not.

          This is not correct.

          Quote
          the voltage after the load may, however, experience a drop,

          I don't know what you mean.  Can you re-phrase?

          Quote
          but that is not the fault of the supply, it is the fault of the load.


          Quote
          By the way -  here's a question:    Does anyone know for sure if it is ok to switch on a modern ps with absolutely nothing plugged into it as a load?

          its ok.

          Ok.
          I didn't know if modern switching supplies were ok with no load or not.

          .



          homer



            Expert
            Re: If a MB dies, is it always worth replacing the PSU as well?
            « Reply #10 on: March 06, 2008, 05:43:15 PM »
            ...
            the voltage at the supply will stay the same regardless if a load is placed on it or not.

            This is not correct.

            what do you mean its not correct? i am sorry if this sounds rude, but what education do you have in electronic circuitry?

            Quote
            I don't know what you mean.  Can you re-phrase?

            http://i195.photobucket.com/albums/z55/anonymous1375/sdafsadf.jpg

            in this picture you can see that the voltage of the 5V DC supply remains at 5V until it passes through the first load. you can see that after the first load, however, there is a voltage drop. there is also a second voltage drop after the second load.




            WillyW



              Specialist
            • Thanked: 29
            • Experience: Experienced
            • OS: Windows XP
            Re: If a MB dies, is it always worth replacing the PSU as well?
            « Reply #11 on: March 06, 2008, 06:03:45 PM »

            ...
            the voltage at the supply will stay the same regardless if a load is placed on it or not.

            This is not correct.

            what do you mean its not correct?

            I mean - in the context of our conversation -  that it is wrong.

            A power supply is designed for a certain voltage at a max given current.

            The condition of  "no load"  is infinite resistance.   Therefore, no current.

            A short would be be zero resistance.  Therefore, in theory,  unlimited current.
            No supply or battery can deliver this.   Thus,  the voltage must fall.   In this extreme example, the voltage would fall to zero.

            Try it.    Get yourself a 12 volt car battery.   Hook your voltmeter leads across it.    Measure the voltage.       Now use a big, heavy set of jumper cables.   Short the battery terminals and watch the voltmeter.  It will fall to almost zero.     Of course,  the cables might melt  and/or the battery might blow.

            So if you operate in between an infinite resistance and a perfect short,  then you can have varying results.    When the impedance of the load is less than the internal impedence of the supply,  you've probably exceeded the design of the supply, and the voltage will fall.... the supply just cannot keep up with the demand for amperage.   

            If you have a defective power supply....  suppose for some reason it can only supply 10 watts and it is a 300 watt supply,   then it doesn't take much of a load before the voltage begins to fall off.   However,  with zero load, the  voltage will be just fine.
             
            Quote
            i am sorry if this sounds rude, but what education do you have in electronic circuitry?

            So far, it is not rude.   It is just not relevant.

            Quote
            Quote
            I don't know what you mean.  Can you re-phrase?

            http://i195.photobucket.com/albums/z55/anonymous1375/sdafsadf.jpg

            in this picture you can see that the voltage of the 5V DC supply remains at 5V until it passes through the first load. you can see that after the first load, however, there is a voltage drop. there is also a second voltage drop after the second load.

            Ah.   An example of a voltage divider.     Earlier it seemed we were talking about just one load,  or the sum total of them all,  as were were talking about measuring the voltage delivered by the supply.






            .



            homer



              Expert
              Re: If a MB dies, is it always worth replacing the PSU as well?
              « Reply #12 on: March 06, 2008, 09:22:23 PM »
              Quote
              Thus,  the voltage must fall.   In this extreme example, the voltage would fall to zero.

              you are incorrect. current and resistance are directly proportional to voltage.

              V (voltage)=I (current) x R (resistance)

              if what you are saying is true then, according to this mathematical formula, electricity would cease to flow once a short circuit is introduced. this would mean it would be impossible to destroy a battery by shorting the two terminals.

              Quote
              If you have a defective power supply....  suppose for some reason it can only supply 10 watts and it is a 300 watt supply,   then it doesn't take much of a load before the voltage begins to fall off.   However,  with zero load, the  voltage will be just fine.

              the voltage will not drop unless there is a problem with the voltage regulators.

              i will go more in depth later, but i am suffering from the flu right now and i can not hold a thought for more then 10 seconds.

              Quote
              Ah.   An example of a voltage divider.

              that was not an example of a voltage divider, it did not have a voltage out, that was an example of a simple series circuit. one must have the resistor there to drop the voltage from 5V to roughly 1.5V, the voltage most common LEDs use. i also included 2 loads to show you that voltage drops happen after the load.

              WillyW



                Specialist
              • Thanked: 29
              • Experience: Experienced
              • OS: Windows XP
              Re: If a MB dies, is it always worth replacing the PSU as well?
              « Reply #13 on: March 07, 2008, 12:32:13 PM »
              Quote
              Thus,  the voltage must fall.   In this extreme example, the voltage would fall to zero.

              you are incorrect.


              Nope.  I'm exactly correct.

              Quote
              current and resistance are directly proportional to voltage.

              V (voltage)=I (current) x R (resistance)

              Right.   

              All three are related.
              Now plug in some numbers.   Remember!... you don't have unlimited current available.

              Here you go:
              Suppose you have a 12V supply that can provide 30 amps.
              If you load it with .8 ohms,  what it be supplying?      15 amps,  right?
              If you load it with .4 ohms,   now it is supplying 30 amps.

              What happens if you load it with .2 ohms?   
              I=E/R    ,   so would current be  60 amps?      Of course not - the ps can't do it.   
              So, we now we have R and I (fixed at 30 max).    E=I*R    ,  thus voltage is
              6V.

              The voltage must fall.

              You were correct in quoting Ohm's Law, and it is the reason the voltage will fall.

              Quote
              if what you are saying is true then, according to this mathematical formula, electricity would cease to flow once a short circuit is introduced.

              In theory,  that is exactly correct.   And it is not what I'm saying,  it is what Ohm said.  :)
              Try it.   Plug numbers into Ohm's Law. 

              Pick a voltage.    12v.   
              0  ohms  - that's your theorectical short circuit ohm value
              I=ER
              I= 12 * 0
              I= 0

              Quote
              this would mean it would be impossible to destroy a battery by shorting the two terminals.

              Because there would no longer be any potential difference in the two terminals.   

              But.... that's not what really happens when you "short" them.     :)

              Quote
              Quote
              If you have a defective power supply....  suppose for some reason it can only supply 10 watts and it is a 300 watt supply,   then it doesn't take much of a load before the voltage begins to fall off.   However,  with zero load, the  voltage will be just fine.

              the voltage will not drop unless there is a problem

              Bingo!
              Now you've got it.    The voltage may drop if there is a problem.
              And this is not what you said earlier:
              "the voltage at the supply will stay the same regardless if a load is placed on it or not."   , that I pointed out was incorrect. 

              Quote
              with the voltage regulators.

              i will go more in depth later, but i am suffering from the flu right now and i can not hold a thought for more then 10 seconds.

              Quote
              Ah.   An example of a voltage divider.

              that was not an example of a voltage divider, it did not have a voltage out, that was an example of a simple series circuit. one must have the resistor there to drop the voltage from 5V to roughly 1.5V, the voltage most common LEDs use. i also included 2 loads

              ??
              Each will have its own voltage drop across it.    Simply measure that, and you'll see.   That's a voltage divider.

              Quote
              to show you that voltage drops happen after the load.

              I don't know what you mean here... voltage drops happen across loads.
              But that is ok....  you seem to want to argue with me,  and I'm not interested in that.     You made a rather blanket statement that was not correct,  and in the interest of the forum readers,  and also to do you a bit of a favor,   I pointed it out.      With Ohm's Law that you are obviously familiar with,  and some consideration about both the theoretical and the real,  you'll grasp it.

              .



              patio

              • Moderator


              • Genius
              • Maud' Dib
              • Thanked: 1769
                • Yes
              • Experience: Beginner
              • OS: Windows 7
              Re: If a MB dies, is it always worth replacing the PSU as well?
              « Reply #14 on: March 07, 2008, 12:55:51 PM »
              Thats not nessaryly true as the board could die from ESD.  How does he really know there bad with out testing them?
              What does this mean ? ?

              patio? ESD Electro Static Discharge.  USe an volt meter and see if it works with a load
              I'm aware of what ESD is...is was asking what this has to do with a PSU issue ? ?
               ???
              " Anyone who goes to a psychiatrist should have his head examined. "