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E5500 - not functioning on AC

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    #1

    E5500 - not functioning on AC

    Schematic:

    Works fine on battery (I do not have one but the seller took a picture), does not charge or run from AC.

    There is a daughterboard with the DC jack on that does not appear in the schematic. When ACIN is read from a point on this board, it gets the full 19V. Yet when it is connected to the motherboard, this voltage falls to about 5.8v - a voltage found in quite a few places around the voltage regs.

    So clearly, the fault is on the motherboard somewhere.

    Volts tested:

    +PWRSRC: generated by BQ24275. Reads 2.45v.
    +PWR_SRC_VCHARGER: 0v
    Suspect the 5.8v is VCHGR, which supplies BQ24275.

    What could be causing this huge drop in voltage? I can't find any shorts anywhere.

    Cheers
    Last edited by spleenharvester; 11-12-2013, 01:47 PM.
    Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD
    Tags: None
    #2
    Re: E5500 - not functioning on AC

    Is this one of the dells that will only work and charge with a dell adapter?
    If it is and the centre pin signal is not correct I dont think it will work.
    Have you another "Proper" dell charger you can try it with.
    Please upload pictures using attachment function when ask for help on the repair
    http://www.badcaps.net/forum/showthread.php?t=39740

    Comment

      #3
      Re: E5500 - not functioning on AC

      Actually that's a good point. I've checked the center pin on that silly 8-pin jack and there is 0v. Could that be the issue?

      Also, the 5.8V is CHAGER_SRC, so at least I have something to work with on this horrid schematic.

      It's a genuine Dell adapter and very deffo working, powers my Dell X1 okay.
      Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

      Comment

        #4
        Re: E5500 - not functioning on AC

        Wait just checked again, apparently the center pin has 13V now. Strange.
        Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

        Comment

          #5
          Re: E5500 - not functioning on AC

          It gets weirder. Certain voltages are present - found +3.3v on both the power button and PC57, which seems to imply TPS51116 is working. When the power button is pressed, there is a "bzzzzzzz" sound on the motherboard.

          All this occurs even while that phantom 6V is there.

          Any ideas?
          Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

          Comment

            #6
            Re: E5500 - not functioning on AC

            too mainstream I know but, shorted capacitor.. maybe ?

            Comment

              #7
              Re: E5500 - not functioning on AC

              Or maybe a value losing component ?

              Comment

                #8
                Re: E5500 - not functioning on AC

                Possible but I'm not entirely sure why a short would pull the adapter down to 6V. Perhaps a resistor gone wonky?

                Plus I've just realised: the fault cannot be on the PWR_SRC line because that would cause the laptop to be completely dead on both AC and battery.

                So the fault must be on either +DC_IN, +DC_IN_SS, PWR_SRC_VCHGR, or +VCHGR.

                CHAGER_SRC is connected to PWR_SRC so the fault can't be there.

                What doesn't help is I can't reliably test any FETS. According to my DMM every single 4835 on the board is open circuit. That's what I get for buying a cheap ass DT830B.
                Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

                Comment

                  #9
                  Re: E5500 - not functioning on AC

                  Okay hang on. Is DCIN the charger or the battery? I can find both ACIN and DCIN on the schematic and I'm not sure if one of them is typo'd (this schematic is full of them) or if one of them refers to battery.
                  Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

                  Comment

                    #10
                    Re: E5500 - not functioning on AC

                    LM393 is recieving 0v even though it should be connected to DC_IN_SS. Also two of its legs read shorted, but I'm not sure which, because there's no orientation markers or anything.
                    Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

                    Comment

                      #11
                      Re: E5500 - not functioning on AC

                      PQ53 - 2N7002 appears to be faulty. Conducts only from source to drain and not source to ground (open circuit). The ones next to it are fine.

                      Could this be dragging the voltage down?

                      (edit, I remember a similar issue on a 6715s, where apparently this was normal? Suddenly not so hopeful)



                      (Note +DC_IN reads 6v, +DC_IN_SS reads about 5.5V)
                      Last edited by spleenharvester; 11-12-2013, 05:59 PM.
                      Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

                      Comment

                        #12
                        Re: E5500 - not functioning on AC

                        While a MOSFET is in OFF state, Its normal to only find the forward bias drop of the body diode, 0.5 to 0.6 volts on diode test.
                        PQ52 is a digital transistor with built in base divider resistors. You will not get normal diode test readings.
                        Its is not possible for a good AC adapter to be continuously loaded to 6v, it would shut down.

                        Comment

                          #13
                          Re: E5500 - not functioning on AC

                          The AC adapter is deffo fine, tried in two other laptops, stable reading of 19.5v.

                          Though my attention has turned back to the DC jack board. Checked again and VIN is 12~13v (it sort of briefly hits 19v and then droops back down). So it's possible the fault is actually there.

                          Though all that's really on the board is a few ceramic caps, inductors and a diode. :s
                          Last edited by spleenharvester; 11-12-2013, 06:31 PM.
                          Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

                          Comment

                            #14
                            Re: E5500 - not functioning on AC

                            More testing. With the DC jack board plugged in, the two outermost terminals (VIN) at the back read 6v.

                            The middle pin reads -1.2v (yes, you read that right).

                            The minus sign caught my attention. Any ideas?
                            Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

                            Comment

                              #15
                              Re: E5500 - not functioning on AC

                              Where are you using as meter ground? Not the LAN socket?
                              Else it is an open in a ground path somewhere maybe.

                              Comment

                                #16
                                Re: E5500 - not functioning on AC

                                Tried several places, including the USB ports and the jack's ground itself. Same readings.

                                Might try removing components from the daughterboard to try and figure out where this drop to 13v is happening.
                                Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

                                Comment

                                  #17
                                  Re: E5500 - not functioning on AC

                                  Try taking measurements with the meter referenced to the outer sleeve of the AC adapter's plug if you can get a probe on to it while its plugged into the laptop.

                                  Comment

                                    #18
                                    Re: E5500 - not functioning on AC

                                    Just tried it, same measurements unfortunately. 6V with daughter+motherboard, 13V on daughterboard only.

                                    EDIT: Wait sorry, misunderstood your comment, I'm getting 19V!
                                    Last edited by spleenharvester; 11-13-2013, 06:11 AM.
                                    Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

                                    Comment

                                      #19
                                      Re: E5500 - not functioning on AC

                                      So I'm guessing there's an open ground somewhere after all?
                                      Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

                                      Comment

                                        #20
                                        Re: E5500 - not functioning on AC

                                        Yes, or the socket is faulty.
                                        Will you update your profile?
                                        I like to see where other members are from.

                                        Comment

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