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    hp elitebook 840 g2 turning on and off

    Please help;
    the above system wit the board number 6050a2637901-mb-a02 turns on and off with the lights on.
    when the system is turned on, the fan spins but it stopped immediately, while the light turns on and off continuously.

    L6100 3.3V
    L6159 5V
    L6200 0v
    L6000 0.6v
    L6300 1v
    L6610 0v

    i checked U6200, the enable pin is 0v

    i flashed the bios, same problem still.

    please help!

    #2
    Re: hp elitebook 840 g2 turning on and off

    Start with the adapter - is it 90W as recommended by the vendor? Does the adapter work ok and supply the DCIN voltage ?

    What is the adapter voltage ?

    Next, remove all power -> meter in resistance mode (2k scale is ok).

    Check if the first 2 mosfets are defective by checking their resistance.

    Measure the resistance between:

    (Mosfet @ Q6010)

    source (1-2-3) & drain (5-6-7-8)
    source (1-2-3) & gate (4)
    gate (4) & drain (5-6-7-8)


    If you see 'OL' = over limit - then increase the resistance scale to the next higher setting on your meter and measure again.

    If you see a low resistance reading, the mosfet is defective and needs to be replaced.

    Repeat the test with the next mosfet @ Q6011 and again Q6012.

    Post the readings.
    Attached Files

    Comment


      #3
      Re: hp elitebook 840 g2 turning on and off

      Originally posted by mon2 View Post
      Start with the adapter - is it 90W as recommended by the vendor? Does the adapter work ok and supply the DCIN voltage ?

      What is the adapter voltage ?

      Next, remove all power -> meter in resistance mode (2k scale is ok).

      Check if the first 2 mosfets are defective by checking their resistance.

      Measure the resistance between:

      (Mosfet @ Q6010)

      source (1-2-3) & drain (5-6-7-8)
      source (1-2-3) & gate (4)
      gate (4) & drain (5-6-7-8)


      If you see 'OL' = over limit - then increase the resistance scale to the next higher setting on your meter and measure again.

      If you see a low resistance reading, the mosfet is defective and needs to be replaced.

      Repeat the test with the next mosfet @ Q6011 and again Q6012.

      Post the readings.


      thank you for your response.

      i believe the mosfets are okay, because there's voltage supply into the system.

      here are what you requested for:

      1. the adapter is rated 90W
      2. all the voltages are okay- 19.83V and 19.26v
      3. there's supply of DCIN voltage
      4. resistances- q6010 89.5k, 205.3k; q6011 205.3k, starts from 20M but continues to drop, reverse prob gives 21.32k; q6012 same with immediate previous, the other side fluctuates in K ohms
      but reverse prob gives 0.562k.

      5. q6011 19.83v; q6012 0.8v.

      in summary voltage gets to r6000.

      I felt RAM voltage missing is the cause of this problem

      Comment


        #4
        Re: hp elitebook 840 g2 turning on and off

        Can you post exactly the requested resistance checks ?

        For each mosfet, in order - otherwise it is very difficult to follow the details.

        source (1-2-3) & drain (5-6-7-8)
        source (1-2-3) & gate (4)
        gate (4) & drain (5-6-7-8)

        Comment


          #5
          Re: hp elitebook 840 g2 turning on and off

          Originally posted by mon2 View Post
          Can you post exactly the requested resistance checks ?

          For each mosfet, in order - otherwise it is very difficult to follow the details.

          source (1-2-3) & drain (5-6-7-8)
          source (1-2-3) & gate (4)
          gate (4) & drain (5-6-7-8)
          ok.

          source and drain- 208k, 350k (prob reversed)
          source and gate- 207.5k, 220.4k (prob reversed)
          gate and drain- 0.577M, 0.577M (prob reversed)

          Comment


            #6
            Re: hp elitebook 840 g2 turning on and off

            Are these measurements for a single or for both mosfets ?

            Comment


              #7
              Re: hp elitebook 840 g2 turning on and off

              Originally posted by mon2 View Post
              Are these measurements for a single or for both mosfets ?
              just q6010.

              these are the readings for the other two fets:

              source (1-2-3) & drain (5-6-7-8)
              source (1-2-3) & gate (4)
              gate (4) & drain (5-6-7-8)

              q6011
              source and drain 0.444M keeps increasing, 168k keeps increasing past 0.444M (reversed probe)
              source and gate 11.81M, ol (rversed probe)
              gate and drain 12.53m, ol (reversed probe)

              q6012
              source and drain 37.32k, starts at 36.7M and decreases after (reversed probe)
              source and gate 246k, starts at 40M fluctuated to ol, drops to 246k (reversed prob)
              gate and drain 249k, 206k

              Comment


                #8
                Re: hp elitebook 840 g2 turning on and off

                q6012
                source and drain 37.32k
                is too low IMHO. Replace Q6012.

                reference (see the resistance table):

                http://electronicsbeliever.com/how-t...0good%20MOSFET.

                Comment


                  #9
                  Re: hp elitebook 840 g2 turning on and off

                  Originally posted by mon2 View Post
                  is too low IMHO. Replace Q6012.

                  reference (see the resistance table):

                  http://electronicsbeliever.com/how-t...0good%20MOSFET.

                  thanks, i will keep you updated

                  Comment


                    #10
                    Re: hp elitebook 840 g2 turning on and off

                    Originally posted by mon2 View Post
                    is too low IMHO. Replace Q6012.

                    reference (see the resistance table):

                    http://electronicsbeliever.com/how-t...0good%20MOSFET.
                    Thank you for this site .
                    Question : i don't understand how you juge that Q6012 is defected !
                    Question : i use always diode mode for my measurements and i think that in doubt i must desoldered the mosfet and take measurements out of board , why you didn't ask for that here!
                    Thank you

                    Comment


                      #11
                      Re: hp elitebook 840 g2 turning on and off

                      Originally posted by Zilicon View Post
                      thanks, i will keep you updated
                      negative!
                      thanks a lot

                      Comment


                        #12
                        Re: hp elitebook 840 g2 turning on and off

                        @mon2 thanks agaain for your assistance.
                        @platinumsteel messaged me privately because he was facing similar issue.

                        i'm going to post the private message here, it might be of help in the future to anyone facing similar hitch.

                        QUOTE=platinumsteel]Hi friend . Have you had any luck with your 840 g2 labtop? I have one with the same issue. Missing ram voltage. I traced it down to a bad cpu/PCH. Did yours had water damage? Mine had some water damage around some 19v mosfets and the cpu line is close to one of those lines so i think the water must of bridged it. But i will check all over again and see if i have a bad Q6010 like you[/QUOTE]


                        so let me dive in. go over the thread that i initiated, you'll see i've narrowed my diagnosis down to u6200 (the chip generating the RAM voltage) because the enable was not present, and of course "PGOOD" signal would be absent as well. on checking, the enable signal was supplied by "SLP_S4#_3R" which is from the CPU.

                        series of questions overwhelmed me, was the CPU bad? or was the BIOS bad?

                        i reprogrammed the BIOS chip, still no success. i was in a dilemma, so i thought to myself to isolate L6200, immediately i saw sign of life. the fan spins at top speed non stop. my enable pin is now present.

                        with L6200 isolated, there's 3.3v enable, there's Vin, but no output. i don't have a donor board, i'm looking into placing an order for the U6200 IC. the IC is "Z1268012" it is different from what's on the schematics.

                        i'll keep you guys updated. thanks

                        Comment


                          #13
                          Re: hp elitebook 840 g2 turning on and off

                          @platinumsteel, i'm sure by now you must have thoroughly cleaned the board. use ultrasonic cleaning if you have one, and if you don't, use isopropyl alcohol to clean the board thoroughly.

                          check if you have a short, the coils if any power rail is shorted. if no short, check the U6200. check the voltage missing. it appears the enable voltage is missing as well. because the enable takes you to the CPU. isolate the L6200 and apply power to the board.

                          my guess is, we might be having same challenges.

                          let's us know as it goes

                          Comment


                            #14
                            Re: hp elitebook 840 g2 turning on and off

                            Originally posted by Zilicon View Post
                            @mon2 thanks agaain for your assistance.
                            @platinumsteel messaged me privately because he was facing similar issue.

                            i'm going to post the private message here, it might be of help in the future to anyone facing similar hitch.

                            QUOTE=platinumsteel]Hi friend . Have you had any luck with your 840 g2 labtop? I have one with the same issue. Missing ram voltage. I traced it down to a bad cpu/PCH. Did yours had water damage? Mine had some water damage around some 19v mosfets and the cpu line is close to one of those lines so i think the water must of bridged it. But i will check all over again and see if i have a bad Q6010 like you

                            so let me dive in. go over the thread that i initiated, you'll see i've narrowed my diagnosis down to u6200 (the chip generating the RAM voltage) because the enable was not present, and of course "PGOOD" signal would be absent as well. on checking, the enable signal was supplied by "SLP_S4#_3R" which is from the CPU.

                            series of questions overwhelmed me, was the CPU bad? or was the BIOS bad?

                            i reprogrammed the BIOS chip, still no success. i was in a dilemma, so i thought to myself to isolate L6200, immediately i saw sign of life. the fan spins at top speed non stop. my enable pin is now present.

                            with L6200 isolated, there's 3.3v enable, there's Vin, but no output. i don't have a donor board, i'm looking into placing an order for the U6200 IC. the IC is "Z1268012" it is different from what's on the schematics.

                            i'll keep you guys updated. thanks[/QUOTE]




                            the ordered IC has arrived and fixed. sadly the problem persists. i traced the fault to U7400, i figured out it was blown. i had it replaced. voila, the system starts and it was stable. voltage is now present at L6200, but the CPU remains cold. L6610 is 0v.

                            meter readings
                            diode mode L6610 0.025
                            resistance mode 44.4

                            the buck converter u6610 has
                            Vin present, PWM present too but no output.
                            does it mean the chip is bad?

                            please help

                            Comment


                              #15
                              Re: hp elitebook 840 g2 turning on and off

                              the PWM is absent, but 5v is present at VDD

                              Comment


                                #16
                                Re: hp elitebook 840 g2 turning on and off

                                what is this in this diagram (d6035) near chargin pin
                                transister or what????? and no
                                Can anybody tell me plzz
                                Attached Files

                                Comment


                                  #17
                                  Re: hp elitebook 840 g2 turning on and off

                                  Originally posted by okrpkcomp View Post
                                  what is this in this diagram (d6035) near chargin pin
                                  transister or what????? And no
                                  can anybody tell me plzz
                                  where are u all guys
                                  ?????
                                  Attached Files

                                  Comment


                                    #18
                                    Re: hp elitebook 840 g2 turning on and off

                                    where are u all guys
                                    ?????
                                    Sleeping. Rest is sometimes required...


                                    See attached. If you copy and paste the markings shown in the schematic, you will find the vendor = PANJIT. They are a company out of Taiwan.

                                    Then go to their website or any of the many resellers of their parts and stuff in the other markings in the schematic.

                                    This is a surface mounted SOT23 packaged DUAL ZENER DIODE rated @ 24 Volts. The drawing of the arrow head with the slanted lines = ZENER diode.

                                    The direction shows that it is a UNIDIRECTIONAL DIODE so the component is protecting only the positive side of the power rail.

                                    In summary, the component will trigger to suppress any voltage > 24 volts on the line. There are 2 diodes in the single package, so it can protect 2 lines.

                                    As long as the voltage on each line remains under 24 volts, this part will not be active. If > 24 volts, it will attempt to suppress the voltage to the save and max value of 24 volts.

                                    The part is not critical and can be purchased from any vendor (does not have to be PANJIT brand). I think my mom makes these. Check your local suppliers for:

                                    'SOT-23 packaged dual zener / tvs / ESD diode @ 24 volts, unidirectional'.

                                    The part should be < $ 1 USD. For sure you can buy from Aliexpress.

                                    PS: If you have a logic board where this part is damaged then this means some in-rush surge was placed on this rail and the component was killed in an attempt to protect the rest of the logic board from being damaged. This can happen in power brown outs, etc. or with a bad power adapter.

                                    Update - the datasheet is attached for this part. Order the version that is rated @ 24 Volts !! Any brand of this part will work - nothing special here to replace this component.
                                    Attached Files
                                    Last edited by mon2; 06-25-2022, 07:41 AM.

                                    Comment


                                      #19
                                      Re: hp elitebook 840 g2 turning on and off

                                      Originally posted by mon2 View Post
                                      Sleeping. Rest is sometimes required...
                                      Salute u sir
                                      Thanksss
                                      Last edited by SMDFlea; 06-25-2022, 08:39 AM.

                                      Comment


                                        #20
                                        Re: hp elitebook 840 g2 turning on and off

                                        The following should work fine to replace this defective component:

                                        ONSEMI ESD7272LT1G
                                        https://cdn.badcaps-static.com/pdfs/...195d4e8444.pdf

                                        ONSEMI SM24T1G
                                        https://cdn.badcaps-static.com/pdfs/...c04ef91804.pdf

                                        ST ESDA25L
                                        https://cdn.badcaps-static.com/pdfs/...5f0415f8e5.pdf

                                        ST ESDA25LY
                                        https://cdn.badcaps-static.com/pdfs/...322e89e16c.pdf

                                        Mouser has the above parts in stock but as noted, you can find them on Aliexpress or mention the details to the store on Aliexpress and they will find a suitable replacement from their local markets.

                                        Comment

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