Locating short circuits with bnch psu

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  • scobie_21
    Senior Member
    • Jul 2011
    • 144

    #1

    Locating short circuits with bnch psu

    Hi Im looking for the quickest way to locate shorts on laptop motherboards. I have a bench supply but every time I connect it the over current trips out and I have to power it off then on again. Is there an easier way of locating suspect component/components?.


    Many thanks
  • smason
    Badcaps Legend
    • Feb 2010
    • 1652
    • Canada

    #2
    Re: Locating short circuits with bnch psu

    Originally posted by scobie_21
    Hi Im looking for the quickest way to locate shorts on laptop motherboards. I have a bench supply but every time I connect it the over current trips out and I have to power it off then on again. Is there an easier way of locating suspect component/components?.


    Many thanks
    A better bench supply?
    Sounds like a smartass reply, but with a good bench supply if you tell it to limit current to 1A, it'll sit there and feed 1A into a dead short or whatever, no need to reset it all the time.

    I find it better to use a good low ohm meter and trace it that way.

    That said, I failed to find a short on a Dell laptop motherboard last month. Tried the give it power and watch for smoke routine, no luck.
    36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....

    Comment

    • scobie_21
      Senior Member
      • Jul 2011
      • 144

      #3
      Re: Locating short circuits with bnch psu

      No not a smart ass reply at all. much appreciated I will look into buying better psu. Can you recommend any ?.

      Comment

      • smason
        Badcaps Legend
        • Feb 2010
        • 1652
        • Canada

        #4
        Re: Locating short circuits with bnch psu

        Originally posted by scobie_21
        No not a smart ass reply at all. much appreciated I will look into buying better psu. Can you recommend any ?.
        There are a lot of similar supplies that look like this Chinese one:

        Item 400396805866 on Ebay.ie (link was too friggin long and I'm too lazy to use a short link site)
        36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....

        Comment

        • scobie_21
          Senior Member
          • Jul 2011
          • 144

          #5
          Re: Locating short circuits with bnch psu

          That's the exact same one I have.

          Comment

          • scobie_21
            Senior Member
            • Jul 2011
            • 144

            #6
            Re: Locating short circuits with bnch psu

            Actually its a slightly different model. Mine has not got the push button in the middle between the current and voltage knobs.

            Comment

            • scobie_21
              Senior Member
              • Jul 2011
              • 144

              #7
              Re: Locating short circuits with bnch psu

              So would I be right in saying I need one with a current limiting feature so it wont power off?.

              Comment

              • rievax_60
                Badcaps Veteran
                • May 2012
                • 897
                • australia

                #8
                Re: Locating short circuits with bnch psu

                I use a 1 ohm resistor in series with my power supply. I try to stay under 0.5A. My power supply is a simple linear design and tends to get rather hot when run at low voltage and high current.

                Comment

                • Th3_uN1Qu3
                  Believe in
                  • Jul 2010
                  • 6031
                  • Romania

                  #9
                  Re: Locating short circuits with bnch psu

                  Originally posted by scobie_21
                  Hi Im looking for the quickest way to locate shorts on laptop motherboards.
                  A milliohm meter.
                  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

                  • rievax_60
                    Badcaps Veteran
                    • May 2012
                    • 897
                    • australia

                    #10
                    Re: Locating short circuits with bnch psu

                    Originally posted by scobie_21
                    So would I be right in saying I need one with a current limiting feature so it wont power off?.
                    Are you starting from zero volts?

                    Comment

                    • scobie_21
                      Senior Member
                      • Jul 2011
                      • 144

                      #11
                      Re: Locating short circuits with bnch psu

                      No Im using 1v. I have a short on a dell motherboard that I cannot locate I have tried isolating different sections by removing some coils on at various regulators. The unit wont power on and the dell psu goes into protection mode after a second or so. I have a bench psu and as the short is on the 1.05v line to the PCh I have established the short is not on the regulator side by removing the coil on the output and the short stays on the output side ie. Pch supply voltage there are many components on that side and my bench meter cuts off after a second or so when I connect it to the circuit.

                      Comment

                      • scobie_21
                        Senior Member
                        • Jul 2011
                        • 144

                        #12
                        Re: Locating short circuits with bnch psu

                        Originally posted by Th3_uN1Qu3
                        A milliohm meter.
                        Can you explain a bit more on the method used please ?

                        Comment

                        • scobie_21
                          Senior Member
                          • Jul 2011
                          • 144

                          #13
                          Re: Locating short circuits with bnch psu

                          Originally posted by rievax_60
                          I use a 1 ohm resistor in series with my power supply. I try to stay under 0.5A. My power supply is a simple linear design and tends to get rather hot when run at low voltage and high current.
                          When you say you try to stay under .5A how do you control this ? I don't seem to have any current limit on my supply It just goes straight to protection mode and I have to switch of the bench psu then on again so theres no chance to find components heating up.

                          Comment

                          • smason
                            Badcaps Legend
                            • Feb 2010
                            • 1652
                            • Canada

                            #14
                            Re: Locating short circuits with bnch psu

                            Originally posted by scobie_21
                            That's the exact same one I have.
                            Hmm does it not have a current adjustment?

                            This is the exact model I have:
                            Attached Files
                            36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....

                            Comment

                            • scobie_21
                              Senior Member
                              • Jul 2011
                              • 144

                              #15
                              Re: Locating short circuits with bnch psu

                              Originally posted by smason
                              Hmm does it not have a current adjustment?

                              This is the exact model I have:
                              The one I have is a Zhaoxin PXN-1505d it looks almost identical to yours except theres no button in the middle for low/high Amp readings. I set the voltage to 1v and no matter what I set the current to as soon as I connact it to the circuit the bench supply just says 00 on both v and current readings and I had to power it off to reset it.

                              Comment

                              • smason
                                Badcaps Legend
                                • Feb 2010
                                • 1652
                                • Canada

                                #16
                                Re: Locating short circuits with bnch psu

                                Originally posted by scobie_21
                                The one I have is a Zhaoxin PXN-1505d it looks almost identical to yours except theres no button in the middle for low/high Amp readings. I set the voltage to 1v and no matter what I set the current to as soon as I connact it to the circuit the bench supply just says 00 on both v and current readings and I had to power it off to reset it.
                                Weird. I can short mine out and it'll limit current but I don't have to power reset it ever.
                                36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....

                                Comment

                                • nucleus
                                  Senior Member
                                  • May 2012
                                  • 64
                                  • Montenegro

                                  #17
                                  Re: Locating short circuits with bnch psu

                                  I also have similar dc power supply and I can set limits on voltage and current. when it reaches it stays there and can works days without problems. same is for short circuits. so probably your have malfunction or something

                                  Comment

                                  • scobie_21
                                    Senior Member
                                    • Jul 2011
                                    • 144

                                    #18
                                    Re: Locating short circuits with bnch psu

                                    Originally posted by nucleus
                                    I also have similar dc power supply and I can set limits on voltage and current. when it reaches it stays there and can works days without problems. same is for short circuits. so probably your have malfunction or something
                                    But what about if you are measuring a dead short on a board ? What does it do then ?.


                                    Thanks for the input

                                    Comment

                                    • nucleus
                                      Senior Member
                                      • May 2012
                                      • 64
                                      • Montenegro

                                      #19
                                      Re: Locating short circuits with bnch psu

                                      Originally posted by scobie_21
                                      But what about if you are measuring a dead short on a board ? What does it do then ?.


                                      Thanks for the input
                                      it reaches limit I set (for example 0.5A), turn on red light that say "I hit the limit" and stays there. thats how it should work every dc power supply I think

                                      Comment

                                      • scobie_21
                                        Senior Member
                                        • Jul 2011
                                        • 144

                                        #20
                                        Re: Locating short circuits with bnch psu

                                        When I adjust the Current without connecting load nothing changes it stays at 0.00A, if I connect say a dc motor the v will go to what I set it to but theres no adjustment on the current it just shows amount of current drawn but is not adjustable

                                        Comment

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