Help! Voltage injection not working

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  • doncius85
    Member
    • Feb 2022
    • 10
    • DE
    #1

    Help! Voltage injection not working

    Hello!
    Need help. Have two different dead laptop motherboards. One has a short on 3V rail, so I'm injecting voltage right there and it draws 8A, but nothing gets hot. Another board has a short on one of the mosfets. When injecting voltage, it draws 7A and the board is dead cold too. I'm inspecting using a thermal cam. What can be wrong? Where does those amps go? Since my power suply has a short circuit protection, for voltage injection I'm using Ni-MH battery, could this be a problem?
    Tags: None
    • reformatt
      Badcaps Legend
      • Feb 2020
      • 1414
      • Australia
      #2
      Re: Help! Voltage injection not working

      Take the heatsink off the CPU and retest. Most shorts of this nature are the CPU/PCH

        Comment

        • CapLeaker
          Leaking Member
          • Dec 2014
          • 8184
          • Canada
          #3
          Re: Help! Voltage injection not working

          if nothing is getting hot, the something is heatsinked pretty heavy...

            Comment

            • petehall347
              Badcaps Legend
              • Jan 2015
              • 4427
              • United Kingdom
              #4
              Re: Help! Voltage injection not working

              about 24w then 0.375 ohms . at 3v .

                Comment

                • doncius85
                  Member
                  • Feb 2022
                  • 10
                  • DE
                  #5
                  Re: Help! Voltage injection not working

                  Heat sinks removed, CPU's not getting warm on both boards. One board reads 0.1Ohm and another 0.2Ohm short. What's strange on the second board, that I'd say 30% of the mosfets reads 8Ohms Source to GND... Is that normal?

                    Comment

                    • reformatt
                      Badcaps Legend
                      • Feb 2020
                      • 1414
                      • Australia
                      #6
                      Re: Help! Voltage injection not working

                      I'd suggest getting something like the Mechanic TS-30A short killer in combination with a thermal camera. Voltage is selectable, and it will pulse on and off when a short is detected. So when a thermal camera is used, it makes the source of the short quite obvious without damaging the board in the process.

                      Don't go above 1V when doing voltage injection. If you have a high side FET shorted in a buck converter for the PCH/CPU/GPU, any volts you inject will end up directly to said components.

                        Comment

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