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    replacing schottky diodes on a AV power supply

    Hi guys, i have a power supply with a shorted SR320 schottky diodes which is in parallel. Only 1 shorted while another is ok. So i removed the faulty one, the power supply is working fine now. SR320 is 3A 20V. I was thinking can i remove both diodes and replace SR340 as 1 diode as it is 3A 40V? Because i dont have SR320. Or can i replace both with SR340?
    Last edited by DjKrish; 08-28-2020, 01:33 AM.

    #2
    Re: replacing schottky diodes on a AV power supply

    neither, your going to need 6A at 20v, not 3A at 40v
    parallel diodes double the current, not the voltage

    if you check my Ryobi charger thread, i replace a couple of diodes with a 25A to220 package part

    Comment


      #3
      Re: replacing schottky diodes on a AV power supply

      Originally posted by stj View Post
      neither, your going to need 6A at 20v, not 3A at 40v
      parallel diodes double the current, not the voltage

      if you check my Ryobi charger thread, i replace a couple of diodes with a 25A to220 package part
      6A 20V, noted, will try that. Cause i fitted the 3A 40V diodes, no power at all. When i fit back the single 3A 20V, its working again.

      Comment


        #4
        Re: replacing schottky diodes on a AV power supply

        higher voltage is fine - infact with schottky's you really want 10x the running voltage.

        https://www.badcaps.net/forum/showthread.php?t=54038

        Comment


          #5
          Re: replacing schottky diodes on a AV power supply

          Originally posted by DjKrish View Post
          6A 20V, noted, will try that. Cause i fitted the 3A 40V diodes, no power at all. When i fit back the single 3A 20V, its working again.
          That does not make any sense.
          What exactly did you put in?
          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


            #6
            Re: replacing schottky diodes on a AV power supply

            Originally posted by budm View Post
            That does not make any sense.
            What exactly did you put in?
            Its a home theaters SMPS. I know, it doesn't makes any sense either. But i dont know, i took out the old one, put in 2 new SR340, power on, no power. Pull out again, put in the old SR320 diode, its working and i was like LOL
            Last edited by DjKrish; 08-28-2020, 07:55 PM.

            Comment


              #7
              Re: replacing schottky diodes on a AV power supply

              I tried the following.

              1 piece of SR340
              2 piece of SR340
              1 piece of SR320 and 1 piece of SR340

              None works. If i pull all and put only 1 piece of SR320, it works. Sighs
              Attached Files
              Last edited by DjKrish; 08-28-2020, 08:11 PM.

              Comment


                #8
                Re: replacing schottky diodes on a AV power supply

                What happen if you test the SR340 and compared to the SR320 with you meter?
                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


                  #9
                  Re: replacing schottky diodes on a AV power supply

                  Originally posted by budm View Post
                  What happen if you test the SR340 and compared to the SR320 with you meter?
                  SR320 - 15.33v
                  SR340 - 5.56v

                  No wonder theres no power when i put SR340. I wonder why

                  Comment


                    #10
                    Re: replacing schottky diodes on a AV power supply

                    i dont understand where you got the numbers,
                    test the diodes with your diode-test on the meter - both directions.

                    Comment


                      #11
                      Re: replacing schottky diodes on a AV power supply

                      Originally posted by stj View Post
                      i dont understand where you got the numbers,
                      test the diodes with your diode-test on the meter - both directions.
                      test on V mode while power on.

                      while take off from board, these are the reading on diode mode

                      sr320 - 0.343v
                      sr340 - 0.164v

                      Comment


                        #12
                        Re: replacing schottky diodes on a AV power supply

                        the sr320 looks fucked for a schottky - thats far too much voltdrop
                        probably damaged - just not as much as the other one.

                        Comment


                          #13
                          Re: replacing schottky diodes on a AV power supply

                          both should be vf 0.55
                          https://cdn.badcaps-static.com/pdfs/...5f72338fd7.pdf
                          Last edited by petehall347; 08-29-2020, 10:34 AM.

                          Comment


                            #14
                            Re: replacing schottky diodes on a AV power supply

                            that's at max current, they generally meter at about 0.18 on a meter

                            Comment


                              #15
                              Re: replacing schottky diodes on a AV power supply

                              Originally posted by stj View Post
                              parallel diodes double the current, not the voltage
                              Theoretically that's correct.

                              However, if the diodes are not built on the same physical die (as is the case here, where O/P has two separate diodes wired in parallel on the PCB), then one diode will run hotter than the other. When that happens, the forward voltage of the hotter diode will drop further, making the the circuit "prefer" to push more current through that diode, which will in turn heat up the diode even more. If this continues, thermal runaway may eventually kill the diode if the circuit has the capacity to push a sufficiently large current through it.

                              Because of that, I agree with what STJ suggested: use a single 6 Amp (or higher) diode/rectifier (and preferably Schottky type for lower losses.)

                              Originally posted by petehall347 View Post
                              That's the maximum expected voltage drop at the rated current of the diode (3 Amps). Most multimeters push much much less than that when testing components (typically in the order of a few uA to maybe a fraction of a mA max.) As such, the Vf will appear much lower. Figure 3 in the above datasheet shows Vf for any given current from 0.1 Amps to rated surge current. You can see that for 0.1 Amps of current, the Vf is around 0.2V for SR320-340. So with a multimeter, the Vf should likely show even lower value... though depending on multimeter quality/design, that may not always be the case.
                              Last edited by momaka; 08-29-2020, 12:50 PM.

                              Comment


                                #16
                                Re: replacing schottky diodes on a AV power supply

                                This is the section. Output is 12V.
                                Attached Files

                                Comment


                                  #17
                                  Re: replacing schottky diodes on a AV power supply

                                  So when you install SR340 you say you no longer get the switched B12V?
                                  When that happens, what Voltage do you get at the Cathode of SR340 with ref to circuit ground?
                                  Is switched B31V present when that happen?
                                  Can you also provide the full PDF of the service manual?
                                  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


                                    #18
                                    Re: replacing schottky diodes on a AV power supply

                                    Originally posted by budm View Post
                                    So when you install SR340 you say you no longer get the switched B12V?
                                    When that happens, what Voltage do you get at the Cathode of SR340 with ref to circuit ground?
                                    Is switched B31V present when that happen?
                                    Can you also provide the full PDF of the service manual?
                                    Heres the pdf file.

                                    Comment


                                      #19
                                      Re: replacing schottky diodes on a AV power supply

                                      Sorry, heres the PDF file
                                      Attached Files

                                      Comment


                                        #20
                                        Re: replacing schottky diodes on a AV power supply

                                        Originally posted by budm View Post
                                        So when you install SR340 you say you no longer get the switched B12V?
                                        When that happens, what Voltage do you get at the Cathode of SR340 with ref to circuit ground?
                                        Is switched B31V present when that happen?
                                        Can you also provide the full PDF of the service manual?
                                        SR340 - 5v plus
                                        SR320 - 12v plus
                                        B31V present

                                        Comment

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