How to check short in power rail

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  • ktmmotocross
    Boardkiller
    • Feb 2014
    • 3575
    • 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?
    Tags: None
    • 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
          • 3575
          • 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
                  • 3575
                  • 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
                          • 3575
                          • 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
                                  • 3575
                                  • 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
                                          • 751
                                          • 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
                                              • 3575
                                              • slovakia
                                              #12
                                              Re: How to check short in power rail

                                              To ground of course.

                                                Comment

                                                • khaahk
                                                  Badcaps Veteran
                                                  • Dec 2013
                                                  • 751
                                                  • 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
                                                          • 3575
                                                          • 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
                                                                  • 3575
                                                                  • 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
                                                                      • 3575
                                                                      • slovakia
                                                                      #18
                                                                      Re: How to check short in power rail

                                                                      I forget the vga rams, it uses 3v

                                                                        Comment

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