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    #1

    Advice needed regarding a broken charging circuit on a lappy

    Hi Guys,

    A friend of mine recently asked me to look at her laptop: its battery charging light constantly flickers whenever the laptop was plugged in to DC and I could not boot the machine.

    I got obtained a charged battery and was able to use it to boot the laptop, I could still not use the DC in to charge or run the lappy without the battery inserted.

    I have opened the laptop up and tested some of the power distribution circuitry and discovered that one of the diodes was not responding the a continuity test.

    As this is affecting charging and the laptop can run from battery I assume this is voltage stabilisation circuity (it sits besides a companion diode).

    This is marked only with a Z4 and I believe it is a COMCHIP CZRW5254B-HF and is apparently a Zener Diode (500mw, Zener Volt : 27, Reverse V: 21).

    This has me wondering:
    Do you guys thing it would be OK to solder over the Surface Mounted Diode as long my external AC > DC remains reliable, effectively shorting it ?

    If not could you guys give me some tips for repairing this:
    I am thinking a standard non surface mounted Diode having its legs soldered to the appropriate pins on the SM-Diode then insulated and put out of the way?

    Thanks Guys
    Tags: None
    #2
    Re: Advice needed regarding a broken charging circuit on a lappy

    Just shorted it with a staple and it now runs off DC

    I will replace the Diode before using a battery

    Any thoughts on the danger this carrys?

    Comment

      #3
      Re: Advice needed regarding a broken charging circuit on a lappy

      Originally posted by Funkimunk View Post
      This has me wondering:
      Do you guys thing it would be OK to solder over the Surface Mounted Diode as long my external AC > DC remains reliable, effectively shorting it ?

      If not could you guys give me some tips for repairing this:
      I am thinking a standard non surface mounted Diode having its legs soldered to the appropriate pins on the SM-Diode then insulated and put out of the way?
      If soldering a SMD component is what is keeping you from using a SMD diode, this video by CuriousInventer is really good at showing how it can be done.

      http://www.youtube.com/watch?v=3NN7UGWYmBY
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      Comment

        #4
        Re: Advice needed regarding a broken charging circuit on a lappy

        Originally posted by retiredcaps View Post
        If soldering a SMD component is what is keeping you from using a SMD diode, this video by CuriousInventer is really good at showing how it can be done.

        http://www.youtube.com/watch?v=3NN7UGWYmBY
        Thank you so much.

        That is a really good video in this case I wouldn't be able to solder directly as the mobo is very congested (there are 3 other SMD components within 2 mm of the varying sides of the diode and a few caps in the area) and I wouldnt trust myself

        The laptop is working at the moment, I simply shorted the diode and it appears to function without issue.

        I do have another board that needs repairing and I think that video will assist me in the repairs.

        Could anyone tell me about the risks associated with soldering over the diode in this charging circuit?

        Thanks again

        Comment

          #5
          Re: Advice needed regarding a broken charging circuit on a lappy

          That diode was probably just for reverse polarity protection, if it works, leave it at that. Its stock adapter can't be polarity reversed anyway.
          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

            #6
            Re: Advice needed regarding a broken charging circuit on a lappy

            Hello all,

            Since i have the exact same fault on a different laptop mobo i thought i'd continue this thread rather than starting a new one.
            Fault - works perfect with a battery but when the AC adapter is plugged in it won't power up or charge the battery.
            On the plus side i managed to source the schematics for it (thanks Google !) which i have attached for you all to examine.
            I am a bit of a newb when it comes to complex circuits but i know how to use a multimeter and i can solder !!

            I'm thinking the fault could be somewhere in the Precharge/Detector circuit which is on page 34

            If anyone can help me get this working i'll be your bud forever
            Attached Files

            Comment

              #7
              Re: Advice needed regarding a broken charging circuit on a lappy

              Bump.....

              A few peeps have viewed the PDF...... any ideas please ?

              Comment

                #8
                Re: Advice needed regarding a broken charging circuit on a lappy

                For a start you could make some measurements based on the schematic. Plug the adapter in and see where in the circuit does its voltage disappear.
                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

                  #9
                  Re: Advice needed regarding a broken charging circuit on a lappy

                  Page 35: VIN -> P2 page 36
                  Page 36: P2 -> PU5 V+
                  Does PU5 lose V+ when the transformer is plugged in?
                  sig files are for morons

                  Comment

                    #10
                    Re: Advice needed regarding a broken charging circuit on a lappy

                    Originally posted by severach View Post
                    Page 35: VIN -> P2 page 36
                    Page 36: P2 -> PU5 V+
                    Does PU5 lose V+ when the transformer is plugged in?
                    Many thanks in helping me with this....

                    Page 35: VIN and P2 measures 19v
                    Page 36: P2 and R254 also measures 19v

                    BR

                    Comment

                      #11
                      Re: Advice needed regarding a broken charging circuit on a lappy

                      Fix for posted problem PQ49 short circuit gate drain source,
                      type AO4407 p-type power trench mosfet,
                      underneath main board,

                      Comment

                        #12
                        Re: Advice needed regarding a broken charging circuit on a lappy

                        Originally posted by Funkimunk View Post
                        Thank you so much.

                        Could anyone tell me about the risks associated with soldering over the diode in this charging circuit? Thanks again
                        A zener diode is a diode that permits current not only in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage or zener voltage. They are used to maintain a certain voltage at a certain point so if shorted could affect the charging circuit. Since all laptops use lithium batteries they turn off the charger when the battery is fully charged to prevent damage to the battery. That could be the circuit affected by the zener diode.

                        Comment

                          #13
                          Re: Advice needed regarding a broken charging circuit on a lappy

                          remember that PQ49 has RDS on of 13 milliohmn at 20v and is a 12A part, replace with identical or equivalent I used fds4435 which was within the spec of what the circuit required,
                          btw to last poster this is the fix! lol

                          Comment

                            #14
                            Re: Advice needed regarding a broken charging circuit on a lappy

                            Did anyone notice these guys on page 33 of the schematic?
                            Attached Files

                            Comment

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