Announcement

Collapse
No announcement yet.

Laptop - Testing shorts on motherboard

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Laptop - Testing shorts on motherboard

    Hi guys,

    But I've been watching the online Electronic Repair School on YouTube. When dealing with a motherboard that has a short, he injects 1-3 amps of current in to the board, to heat up the failing component (which carries most of the current) and then he touches the board so as to find out which component is failing. I've read about this technique many times before.

    https://www.youtube.com/channel/UCoo...Z0PFAPc4Ymg3RA

    I want to use this trick on a few boards that I have here to try to identify the failing component, but I don't have a desk power supply. Has anybody done something like this with a battery? I could just set up a battery with a high wattage, low resistance resistor to do the same surely?

    #2
    Re: Laptop - Testing shorts on motherboard

    It's very useful to be able to control the voltage and limit the current you inject. If you're short on money and just want to play with boards you can buy a DPS3012 module. It also shows you the amperage and wattage directly so you don't have to measure/calculate manually.
    OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

    Comment


      #3
      Re: Laptop - Testing shorts on motherboard

      Voltage injection using a battery has two cases:
      1- If the battery provides high current, it is not recommended to use because it cannot be controlled.
      2- If the battery does not provide high current, it can be used but it is weak.
      As a conclusion, battery is not a good power source in finding a short circuit.
      Last edited by caspian; 03-13-2018, 03:35 AM.

      Comment


        #4
        Re: Laptop - Testing shorts on motherboard

        good discussion sir. im looking forward to this topic

        Comment


          #5
          Re: Laptop - Testing shorts on motherboard

          Originally posted by caspian View Post
          Voltage injection using a battery has two cases:
          1- If the battery provides high current, it is not recommended to use because it cannot be controlled.
          2- If the battery does not provide high current, it can be used but it is weak.
          As a conclusion, battery is not a good power source in finding a short circuit.
          My idea was to use two 12V batteries in series, then feed it to whatever voltage regulator chip I needed, and on the output I could use a high wattage resistor to limit the current (since the larger battery will output too much current and the small battery will output too little, as you said). This would lack the accuracy of a proper voltage/current supply. The more I got thinking about it, I think it might be better that I just choose a cheap supply that will do the job.

          Given the price of that other little box that was mentioned by piernov, I might just buy one of those.



          Now I wouldn't say it's the prettiest device that I will have ever seen. But if it does the job !! And it's got great reviews.

          I'll see if I can get one here in Ireland.

          Comment


            #6
            Re: Laptop - Testing shorts on motherboard

            Founds somebody on a Craiglist type site here who is selling a DPS5020 which is 0-30V, 0-20A, 480W. I've put in an offer.

            Looks like I may be looking forward to a weekend of blowing up laptop boards. :-)

            Comment


              #7
              Re: Laptop - Testing shorts on motherboard

              Getting that power supply is a good idea, it will serve you well.

              Alternatively, you could buy a defective MXM video card, use a heatgun to remove the video chip (no finesse needed here as you won't be using the GPU again), clean the old solder and strap the core regulator to run as soon as you apply power. Then solder some nice thick cables directly to the tantalum capacitors on the output. It will give around 1 volt at 15-20A or more, high enough current to bust any component that has gone low resistance, low enough voltage to not damage anything else, and it is inherently short-circuit protected - "idiot proof" if you accidentally cross the output cables.

              It is a bit of work but old MXM cards with dead GPUs are cheap and you can use any laptop adapter that you already have lying around, to feed it.
              Originally posted by PeteS in CA
              Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
              A working TV? How boring!

              Comment


                #8
                Re: Laptop - Testing shorts on motherboard

                Ordered my power supply. it's due in tomorrow. I probably should have bought one years ago, but looking for to getting some use out of it when it arrives.

                And while looking on youtube I actually found somebody who was using the same idea I had. Battery to supply voltage, large wattage resister to limit the current.

                https://youtu.be/XhqwC3BFBug?t=187

                Its the Grants Pass guy, who fixes TVs.

                Comment


                  #9
                  Re: Laptop - Testing shorts on motherboard

                  The problem with using just a series resistor is that if you blow open the shorted part (which happens every once in a while), you will have the full battery voltage applied to that rail, which may not be too good of an idea.
                  Originally posted by PeteS in CA
                  Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                  A working TV? How boring!

                  Comment


                    #10
                    Re: Laptop - Testing shorts on motherboard



                    I bought this from a local wholesaler in Dublin, Farnells. They are good, very fast and efficient. I'm normally a fan of the "quick start" instructions, but the ones that came with this were far below what would be required for somebody to be able to use the product. It essentially can be boiled down to "Press the big ON button and fiddle around with the knobs on the front". After a bit of messing around with a few motors, I got the hang of the CC and CV settings, so I'm up and running now.

                    Unfortunately, the laptop (with the short) that I was hoping to troubleshoot has gone back to the user - he's agreed a fix price with HP. I'm disappointed as I hate sending back anything without first have been afforded the opportunity to blow the crap out of it.

                    Comment


                      #11
                      Re: Laptop - Testing shorts on motherboard

                      How much are this power supply ??? JonathanAnon . I buy Zahoxine but its not good ..its disturb after 1 year..........

                      Comment


                        #12
                        Re: Laptop - Testing shorts on motherboard

                        I bought that one for about 100 euro + shipping. There are other versions of the same product, essentially with the same chassis but different internal components. The version that I bought is the 5 amp version, but I think you can get the 3V version for about 60 euro + shipping.

                        Comment


                          #13
                          Re: Laptop - Testing shorts on motherboard

                          On some cases I use bench PSU adjusted to low voltage and current as high as can get,sometimes works sometimes not.
                          In cases when is strong short, I use one pack of 18650 (4 in parallel) that way either short or pcb traces will blow.Lucky me until now only short blow and no traces.
                          Since thermal camera is expensive, I use fax paper or other thermal paper when is hard to identify which component is heating.
                          Another ideea for low voltage rails is to use some super capacitors, charge them to required voltage 1.8V 2.8V etc then connect to shorted power rail.

                          Comment


                            #14
                            Re: Laptop - Testing shorts on motherboard

                            Cic smb short locator
                            Attached Files

                            Comment

                            Working...
                            X