Shorted diode, help to identify it

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  • Ilyushin
    Member
    • Jun 2014
    • 11
    • Spain

    #1

    Shorted diode, help to identify it

    Hi, I have this laptop and I need help to find with what to replace it

    Packard Bell mit-drag-gt2
    Motherboard Hannstar J MV-4 94V-0 0648

    It was in short-circuit and I found that the cause was a shorted diode. I removed it and it has no resistance no matter what direction (anode to cathode or reverse)

    With that diode removed, the board has no short-circuit.

    I haven't found any schematic for this board, and in the PCB under the diode is printed its symbol, so it's not a zener (attached pic)

    The diode only has a yellow stripe on it. I found on other laptops what seems the same diode but with black stripe instead.

    Any help to identify it? Thanks
    Attached Files
    Last edited by Ilyushin; 07-14-2014, 02:47 PM.
  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: Shorted diode, help to identify it

    "It was in short-circuit and I found that the cause was a shorted diode. I removed it and it has no resistance no matter what direction (anode to cathode or reverse)" OK, it is alittle confused here, you found diode that tested shorted when is still soldered to the board, then you removed that diode and tested again and it shows NO RESISTANCE NO MATTER WHAT DIRECTION, do you mean it shows < 1 Ohm in both direction or it shows infinite resistance?
    Last edited by budm; 07-14-2014, 03:42 PM.
    Never stop learning
    Basic LCD TV and Monitor troubleshooting guides.
    http://www.badcaps.net/forum/showthr...956#post305956

    Voltage Regulator (LDO) testing:
    http://www.badcaps.net/forum/showthr...999#post300999

    Inverter testing using old CFL:
    http://www.badcaps.net/forum/showthr...er+testing+cfl

    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
    http://s807.photobucket.com/user/budm/library/

    TV Factory reset codes listing:
    http://www.badcaps.net/forum/showthread.php?t=24809

    Comment

    • selldoor
      Slow Learner
      • Dec 2010
      • 7870

      #3
      Re: Shorted diode, help to identify it

      Well looks like it may not be shorted - when you have worked that out this may help with ID
      http://www.marsport.org.uk/smd/sod80.htm
      Please upload pictures using attachment function when ask for help on the repair
      http://www.badcaps.net/forum/showthread.php?t=39740

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #4
        Re: Shorted diode, help to identify it

        That is a good link, selldoor.
        Never stop learning
        Basic LCD TV and Monitor troubleshooting guides.
        http://www.badcaps.net/forum/showthr...956#post305956

        Voltage Regulator (LDO) testing:
        http://www.badcaps.net/forum/showthr...999#post300999

        Inverter testing using old CFL:
        http://www.badcaps.net/forum/showthr...er+testing+cfl

        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
        http://s807.photobucket.com/user/budm/library/

        TV Factory reset codes listing:
        http://www.badcaps.net/forum/showthread.php?t=24809

        Comment

        • Ilyushin
          Member
          • Jun 2014
          • 11
          • Spain

          #5
          Re: Shorted diode, help to identify it

          Sorry if it wasn't well explained

          The diode removed, shows 0 resistance no matter what direction. This is the same values measured when it was soldered, and what caused the short in the mainboard between the +19v input and gnd

          Looking in the link provided by selldoor seems that it should be a zener? but the symbol in the pcb where it was soldered is the symbol of a simple diode, not a zener

          Or could it be a switching one as that link says?
          Last edited by Ilyushin; 07-14-2014, 04:13 PM.

          Comment

          • budm
            Badcaps Legend
            • Feb 2010
            • 40746
            • USA

            #6
            Re: Shorted diode, help to identify it

            So the anode is connected directly to ground and the Cathode is connected directly to the +19VDC input? Is that correct?
            Never stop learning
            Basic LCD TV and Monitor troubleshooting guides.
            http://www.badcaps.net/forum/showthr...956#post305956

            Voltage Regulator (LDO) testing:
            http://www.badcaps.net/forum/showthr...999#post300999

            Inverter testing using old CFL:
            http://www.badcaps.net/forum/showthr...er+testing+cfl

            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
            http://s807.photobucket.com/user/budm/library/

            TV Factory reset codes listing:
            http://www.badcaps.net/forum/showthread.php?t=24809

            Comment

            • Ilyushin
              Member
              • Jun 2014
              • 11
              • Spain

              #7
              Re: Shorted diode, help to identify it

              Yes, Anode goes to GND and Cathode goes to the +19v input through 2 "PL" that are inductors if i'm right.

              Attached photo, where the red wire was soldered (for finding the short) is the +19 input
              Attached Files

              Comment

              • atsio
                Badcaps Veteran
                • Oct 2013
                • 819
                • Greece

                #8
                Re: Shorted diode, help to identify it

                Usually Mitac designs (like yours) are using this http://my.mouser.com/ProductDetail/T...3NuWCW%252bQ==

                Comment

                • Ilyushin
                  Member
                  • Jun 2014
                  • 11
                  • Spain

                  #9
                  Re: Shorted diode, help to identify it

                  Originally posted by atsio
                  Usually Mitac designs (like yours) are using this http://my.mouser.com/ProductDetail/T...3NuWCW%252bQ==
                  thanks for your reply, but that link shows a Zener diode, and mine is not a Zener, based on the drawing of the pcb

                  Comment

                  • selldoor
                    Slow Learner
                    • Dec 2010
                    • 7870

                    #10
                    Re: Shorted diode, help to identify it

                    You cant always trust the markings on the boards - may have originally been going to have an ordinary diode then decided to switch to a zener and didnt alter the silkscreening.
                    Please upload pictures using attachment function when ask for help on the repair
                    http://www.badcaps.net/forum/showthread.php?t=39740

                    Comment

                    • cdicky
                      Member
                      • Jul 2014
                      • 27
                      • England

                      #11
                      Re: Shorted diode, help to identify it

                      You have to ask yourself for why would a diode be connected to ground ??

                      Any chance you can follow and trace a circuit around it. It might help identify what its purpose was and figure out what it should be, rather than guessing what it was.

                      Comment

                      • atsio
                        Badcaps Veteran
                        • Oct 2013
                        • 819
                        • Greece

                        #12
                        Re: Shorted diode, help to identify it

                        Originally posted by Ilyushin
                        thanks for your reply, but that link shows a Zener diode, and mine is not a Zener, based on the drawing of the pcb
                        Do not take note of the drawing on the board. All the markings usually on boards are for diodes although there is a zener on that position

                        Comment

                        • Ilyushin
                          Member
                          • Jun 2014
                          • 11
                          • Spain

                          #13
                          Re: Shorted diode, help to identify it

                          thanks everyone for helping. So, can we conclude it's the zener atsio posted in #8?

                          #11 I'm afraid that's far above from my understanding...

                          Comment

                          • selldoor
                            Slow Learner
                            • Dec 2010
                            • 7870

                            #14
                            Re: Shorted diode, help to identify it

                            looks to me like it goes to r103 not to ground? there is a trace under your arrow?
                            Please upload pictures using attachment function when ask for help on the repair
                            http://www.badcaps.net/forum/showthread.php?t=39740

                            Comment

                            • ktmmotocross
                              Boardkiller
                              • Feb 2014
                              • 3573
                              • slovakia

                              #15
                              Re: Shorted diode, help to identify it

                              its just diode on ground, replace with any of diode to 30v and u r good to go
                              Last edited by ktmmotocross; 07-15-2014, 01:09 PM.

                              Comment

                              • budm
                                Badcaps Legend
                                • Feb 2010
                                • 40746
                                • USA

                                #16
                                Re: Shorted diode, help to identify it

                                It looks to me from the pictures, the Anode is connected to two resistors (connected in parallel) PR51, PR66, the other two ends of the resistors are connected to the B+ large pad on the left side of the PQ10 (MOSFET?).
                                I doubt that this diode is used as a crowbar protection device in case the polarity of the power supply is reverse, which in that case, the Diode will be bias on and will cause the fuse to blow, the diode will be much bigger size to handle the crowbar current.
                                Never stop learning
                                Basic LCD TV and Monitor troubleshooting guides.
                                http://www.badcaps.net/forum/showthr...956#post305956

                                Voltage Regulator (LDO) testing:
                                http://www.badcaps.net/forum/showthr...999#post300999

                                Inverter testing using old CFL:
                                http://www.badcaps.net/forum/showthr...er+testing+cfl

                                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                http://s807.photobucket.com/user/budm/library/

                                TV Factory reset codes listing:
                                http://www.badcaps.net/forum/showthread.php?t=24809

                                Comment

                                • selldoor
                                  Slow Learner
                                  • Dec 2010
                                  • 7870

                                  #17
                                  Re: Shorted diode, help to identify it

                                  Originally posted by budm
                                  It looks to me from the pictures, the Anode is connected to two resistors (connected in parallel) PR51, PR66, the other two ends of the resistors are connected to the B+ large pad on the left side of the PQ10 (MOSFET?).
                                  Me too - I put the value instead of the board designator
                                  Please upload pictures using attachment function when ask for help on the repair
                                  http://www.badcaps.net/forum/showthread.php?t=39740

                                  Comment

                                  • Ilyushin
                                    Member
                                    • Jun 2014
                                    • 11
                                    • Spain

                                    #18
                                    Re: Shorted diode, help to identify it

                                    Hi everyone

                                    So... I found in some monitor scrap-power board a diode that looked exactly the same, and that tested good when I removed it. (flow in one direction, not in reverse)

                                    I put in the laptop board and there wasn't any short-circuit. Then I ensemble everything, connect to DC adapter and there was a slight "click" sound.

                                    No power-up at all, and now the laptop board is again in short-circuit. I have done again the "method" to locate the cause of the short (bench power supply and where it got hot), and again is the diode's fault. Diode removed and no short

                                    So, any suggestions? what can be causing the diode to die "open"?

                                    Comment

                                    • budm
                                      Badcaps Legend
                                      • Feb 2010
                                      • 40746
                                      • USA

                                      #19
                                      Re: Shorted diode, help to identify it

                                      Since the Anode is not directly connected to Ground pad, with diode removed, what resistance do you get between the chassis ground and the Anode, Chassis Ground and Cathode? It seems to me that too much current was flowing through the diode and caused the damage to the Diode.
                                      Never stop learning
                                      Basic LCD TV and Monitor troubleshooting guides.
                                      http://www.badcaps.net/forum/showthr...956#post305956

                                      Voltage Regulator (LDO) testing:
                                      http://www.badcaps.net/forum/showthr...999#post300999

                                      Inverter testing using old CFL:
                                      http://www.badcaps.net/forum/showthr...er+testing+cfl

                                      Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                      http://s807.photobucket.com/user/budm/library/

                                      TV Factory reset codes listing:
                                      http://www.badcaps.net/forum/showthread.php?t=24809

                                      Comment

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