How to check short in power rail

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  • ktmmotocross
    Boardkiller
    • Feb 2014
    • 3573
    • slovakia

    #1

    How to check short in power rail

    Hello i need to know how to check short in power rails. I have some short in power rails and i check resistance but on processor, VGA or chipset i get resistence under 1ohm.
    anybody know how to chceck that short?
  • loser18
    Badcaps Veteran
    • Nov 2013
    • 274
    • UK

    #2
    Re: How to check short in power rail

    Take out the CPU...check again...should have some resistance now...GPU & GMCH have sometimes low resistance eg. 10-15ohms...

    Comment

    • ktmmotocross
      Boardkiller
      • Feb 2014
      • 3573
      • slovakia

      #3
      Re: How to check short in power rail

      yes i know that i take out processor i have some resistance but in GPU or chipset i get resistance less then ohm about 0.2ohm.

      Comment

      • loser18
        Badcaps Veteran
        • Nov 2013
        • 274
        • UK

        #4
        Re: How to check short in power rail

        What's the mobo model number...

        Comment

        • ktmmotocross
          Boardkiller
          • Feb 2014
          • 3573
          • slovakia

          #5
          Re: How to check short in power rail

          its HP dv6700 with nvidia GPU, it shuts right after power switch. its so fast that i cannot check power on power rails and resistance dont show enything

          Comment

          • loser18
            Badcaps Veteran
            • Nov 2013
            • 274
            • UK

            #6
            Re: How to check short in power rail

            Here's schematic if it's AT3...
            Which coils are shorted?
            Attached Files

            Comment

            • ktmmotocross
              Boardkiller
              • Feb 2014
              • 3573
              • slovakia

              #7
              Re: How to check short in power rail

              not mine board. i have Nvidia MCP chipset and Turion processor.
              PL3 - 0.2ohm
              PL11 - 0.2ohm
              PQ25 - output - 0.3ohm
              here is diagram
              https://cdn.badcaps-static.com/pdfs/...f1d82042d0.pdf

              Comment

              • loser18
                Badcaps Veteran
                • Nov 2013
                • 274
                • UK

                #8
                Re: How to check short in power rail

                If you don't have lab PSU it's a pain in the arse to look for shorted components...
                Desolder PL3 & PL11 and check which pin/side is shorted...

                Comment

                • ktmmotocross
                  Boardkiller
                  • Feb 2014
                  • 3573
                  • slovakia

                  #9
                  Re: How to check short in power rail

                  How can PSU help me to detect vhere i have short?

                  Comment

                  • loser18
                    Badcaps Veteran
                    • Nov 2013
                    • 274
                    • UK

                    #10
                    Re: How to check short in power rail

                    You will inject voltage to shorted rail & look for components which are heating up...
                    Need a proper lab PSU with voltage & current regulator...

                    Comment

                    • khaahk
                      Badcaps Veteran
                      • Dec 2013
                      • 749
                      • Estonia

                      #11
                      Re: How to check short in power rail

                      What do you mean by PL3 - 0.2 ohm ?
                      Are you measuring resistance across PL3 or measuring from PL3 relative to GND?

                      Originally posted by ktmmotocross
                      not mine board. i have Nvidia MCP chipset and Turion processor.
                      PL3 - 0.2ohm
                      PL11 - 0.2ohm
                      PQ25 - output - 0.3ohm
                      here is diagram
                      https://cdn.badcaps-static.com/pdfs/...f1d82042d0.pdf

                      Comment

                      • ktmmotocross
                        Boardkiller
                        • Feb 2014
                        • 3573
                        • slovakia

                        #12
                        Re: How to check short in power rail

                        To ground of course.

                        Comment

                        • khaahk
                          Badcaps Veteran
                          • Dec 2013
                          • 749
                          • Estonia

                          #13
                          Re: How to check short in power rail

                          Sorry, just checking...
                          Then lab PSU is the easiest way.
                          Way too many shorts for one mainboard (or do they all end in nvidia mcp67)?

                          Comment

                          • loser18
                            Badcaps Veteran
                            • Nov 2013
                            • 274
                            • UK

                            #14
                            Re: How to check short in power rail

                            Had shorted 19V rail...
                            Found 2 shorted FETs today (without PSU)...
                            Didn't take more than 15min...
                            Also had to use boardview file as no markings on board itself...
                            Was like schematic-boardview-mobo-desolder lol

                            Possible, if you following schematics...(but still pain in the arse)

                            Comment

                            • ktmmotocross
                              Boardkiller
                              • Feb 2014
                              • 3573
                              • slovakia

                              #15
                              Re: How to check short in power rail

                              i think its that mcp, because it have 1,2 and 3v and all this power rails is shorted. removed pl3 and pl11 and short is on chips side. gpu uses only 1.2v so i think MCP is shorted.

                              Comment

                              • loser18
                                Badcaps Veteran
                                • Nov 2013
                                • 274
                                • UK

                                #16
                                Re: How to check short in power rail

                                Need to reball...or try reflow if You don't have bga machine...
                                Also did you check PC43, 44, 45, 113, 19, 111, 13, 109 and PU1?

                                They're most likely ok, but you never know...
                                Last edited by loser18; 05-17-2014, 04:33 PM.

                                Comment

                                • ktmmotocross
                                  Boardkiller
                                  • Feb 2014
                                  • 3573
                                  • slovakia

                                  #17
                                  Re: How to check short in power rail

                                  damn have a bad luck. Unsolder MCP > nochange still short 1.2v and 3v

                                  so i desoldered GPU and all shorts is gone.
                                  I dont have a knowledge that GPU uses 3V rail

                                  Comment

                                  • ktmmotocross
                                    Boardkiller
                                    • Feb 2014
                                    • 3573
                                    • slovakia

                                    #18
                                    Re: How to check short in power rail

                                    I forget the vga rams, it uses 3v

                                    Comment

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