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Dell Latitude E6420 Charging and Power Problem

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    Dell Latitude E6420 Charging and Power Problem

    I have Dell Latitude E6420 Charging and Power Problem. First laptop was fine but it did not charge battery. When checked with new battery it would detect battery and worked on charged battery but wouldn't charge it. Tested with identical used laptop at computer shop and the other laptop charged the new battery. So I ended up not buying battery.

    After opening the laptop I notice 3 or 4 total capacitors shorted to ground on both sides of the board. I removed all and tested and they are not short. While taking measurement on the board, after measuring one of the capacitors, suddenly I noticed the power LED went off. Then instantly I notice the charging ic (PU11) get very hot. I removed PQ33 and it seems fine. So thinking it might be charging ic, I removed it but still I have shorted to ground readings on the following caps.

    1. Cap above PQ27 next to PL4
    2. Small Cap to right of PQ37
    3. Cap below PJP34
    4. Small Cap below PQ33
    5. Both Caps above PU11 charging ic ISL 88731c or BQ24747

    Also PD6 is giving me 4 readings. Is that normal?
    I have not removed the capacitor to right of PQ37 and checked.
    Board is PAL LA-6591-P Rev 2.0. I have found the Rev 1.0 schematics but it is difficult to follow since all components are not labeled on the board. Any help to isolate the problem is appreciated.

    Photo links below. Won't let me post in this thread.
    https://ibb.co/zh4Vv0j
    https://ibb.co/tDR3jj7
    Attached Files
    Last edited by SuperAman; 07-25-2020, 02:39 PM.

    #2
    Re: Dell Latitude E6420 Charging and Power Problem

    Try to locate PR205 and see if it is shorted to GND.

    Comment


      #3
      Re: Dell Latitude E6420 Charging and Power Problem

      Originally posted by mcplslg123 View Post
      Try to locate PR205 and see if it is shorted to GND.
      PR205 and PR227 are shorted to ground on both sides 002 and 003 readings.

      Comment


        #4
        Re: Dell Latitude E6420 Charging and Power Problem

        Originally posted by SuperAman View Post
        PR205 and PR227 are shorted to ground on both sides 002 and 003 readings.
        Remove PR205 and check which pad is shorted to gnd. Inject voltage on the shorted side of PR205. Dont exceed 1V though you can increse amp. Check consumption on dc bench supply and look for hot component on mb. I assume you have dc lab psu.

        Comment


          #5
          Re: Dell Latitude E6420 Charging and Power Problem

          Originally posted by mcplslg123 View Post
          Remove PR205 and check which pad is shorted to gnd. Inject voltage on the shorted side of PR205. Dont exceed 1V though you can increse amp. Check consumption on dc bench supply and look for hot component on mb. I assume you have dc lab psu.
          I will try tomorrow by removing PR205. My DC supply is only up to 15v and 2a maximum. But now with charging ic removed and charger connected PQ4 heats up.

          Comment


            #6
            Re: Dell Latitude E6420 Charging and Power Problem

            You should,nt power up the mb without charging IC.

            Comment


              #7
              Re: Dell Latitude E6420 Charging and Power Problem

              Originally posted by mcplslg123 View Post
              You should,nt power up the mb without charging IC.
              I removed the charging ic because it was getting hot when charger was connected. So should I replace it with a new one or the same one? I have the exact ic from a spare board.

              Comment


                #8
                Re: Dell Latitude E6420 Charging and Power Problem

                Replace with another one from scrap mb.

                Comment


                  #9
                  Re: Dell Latitude E6420 Charging and Power Problem

                  I have removed PR227 and checked and found one side is short to ground. I have tried to give voltage 1v but current is less than 1a my supply is 2a max so nothing is really heating up. But testing I find that PQ31 all 8 legs are shorted to each other and ground. Is this my faulty component? My charging coil is also short to ground on both sides. PQ31 & PQ33 are charging gates so is it possible this shorted PQ is causing all the shorted caps and not charging problem.

                  Comment


                    #10
                    Re: Dell Latitude E6420 Charging and Power Problem

                    ^ post I meant to say I removed PR205. PR227 is short to ground on both sides, I have not removed it to check yet.

                    Comment


                      #11
                      Re: Dell Latitude E6420 Charging and Power Problem

                      Remove PQ31 from mb and test it outside between PIN1-4/PIn1-5/Pin4-8 in diode mode. If it buzzes in all 3 ways its definitely shorted. Do repeat the same check on mb pads after removing PQ31.

                      Comment


                        #12
                        Re: Dell Latitude E6420 Charging and Power Problem

                        Originally posted by SuperAman View Post
                        I have removed PR227 and checked and found one side is short to ground. I have tried to give voltage 1v but current is less than 1a my supply is 2a max so nothing is really heating up. But testing I find that PQ31 all 8 legs are shorted to each other and ground. Is this my faulty component? My charging coil is also short to ground on both sides. PQ31 & PQ33 are charging gates so is it possible this shorted PQ is causing all the shorted caps and not charging problem.

                        If charging ic see short on main 19V line it turn off two main mosfets

                        check all highside mosfets for short and u can inject even 20V, but u need to have current max 1A
                        Last edited by ktmmotocross; 08-09-2020, 11:41 PM.

                        Comment


                          #13
                          Re: Dell Latitude E6420 Charging and Power Problem

                          Originally posted by ktmmotocross View Post
                          If charging ic see short on main 19V line it turn off two main mosfets

                          check all highside mosfets for short and u can inject even 20V, but u need to have current max 1A
                          Thanks. With power ic removed, PR205 and PQ31 & PQ33 all removed all the shorted caps are no longer short except for the small cap next to PL4 and PL4 is also short to ground on the board. Is there another component that is causing the coil and cap to read short to ground on both sides?

                          Comment


                            #14
                            Re: Dell Latitude E6420 Charging and Power Problem

                            In my country I am unable to buy SI4812DY (PQ33), it has schotky diode. I found a similar mosfet with schotky diode but the (VGS) was 12v, I need 20v. Do I need to replace with a mosfet that has schotky or will a similar rated N Channel mosfet work?

                            Comment

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