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    Philips 40PFL3505D/F7 Question about FET replacment

    Hi, was told this TV was damaged by lightning. Unfortunately after I got it home I noticed someone had been tinkering inside already. Good lesson to check the screws in the back before hand.

    Anyways I found a shorted transistor, Q601 that has part # 2SK3798.
    http://www.digikey.com/product-detai...QM)-ND/2062700

    I can get that part used on ebay or from China, but Im wondering if this one would be a safe replacement:
    http://www.digikey.com/product-detai...4QM)-ND/871460

    The main thing I see different is it's rated for 3A current as opposed to 4A on the original. Thanks for any input!
    Attached Files

    #2
    Re: Philips 40PFL3505D/F7 Question about FET replacment

    It need to have the same or better, not lower spec than the original. This two-transistor switching power supply when it goes bad, the MOSFET, the small transistor, Zener diodes, Diodes, opto in that section need to checked.
    Same circuits used in Emerson/Sylvania. Also the rectifier diodes in the cold side.
    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


      #3
      Re: Philips 40PFL3505D/F7 Question about FET replacment

      This would be closer (5A) and sold min qty 1,

      http://www.digikey.com/product-detai...5QM-ND/1692460
      Attached Files
      Last edited by tw2005; 05-04-2013, 09:14 PM.

      Comment


        #4
        Re: Philips 40PFL3505D/F7 Question about FET replacment

        Thanks!

        Comment


          #5
          Re: Philips 40PFL3505D/F7 Question about FET replacment

          I've been working on this on and off for a bit now..

          Here's what I've done so far..

          After trying to repair the original PS board with no luck I decided to order a new one since someone attempted repair before and I didn't know what had been done and diodes were missing, etc.

          The new board came and when plugged in some diodes shorted again. I wasn't able to use light bulb method on this one as it kept clicking relay and shutting down.

          Long story short I eventually determined the digital main board had a short on the P-ON+3.3V line that was causing the damage to the PS board.

          I replaced digital main board and the shorted diodes on the new PS board and finally the TV started up, backlight came on but no video.

          So I pulled the T-Con and the fuse F1 was blown, to the left D1 shows shorted in circuit as well as several of the caps above. Im guessing the lightning took out D1 before the fuse blew but haven't removed it yet.

          I've put too much $ in this one so far and although I can get the T-Con for around $20 I'd like to try to replace the fuse and diode, if it turns out the diode is bad.

          But looking at the markings on the diode all I can make out is a BK and either LL or and F.

          Anyone have info on this diode? T-Con Part # is Samsung LJ94-03281G. Thanks!

          Im hopeful I can repair original PS board now that I've found the underlying issue and recoup some $.

          This is most extensive damage I've seen to a TV it basically caused damage to diodes and a transistor on power supply, a diode on jack board, main board, and now t-con..
          Attached Files
          Last edited by kevinm34232; 05-22-2013, 09:42 PM.

          Comment


            #6
            Re: Philips 40PFL3505D/F7 Question about FET replacment

            Update:

            Removed D1, it is shorted. Short went away on board. Just have to find a suitable replacement now.

            Hoping someone has had this problem before!

            Comment


              #7
              Re: Philips 40PFL3505D/F7 Question about FET replacment

              Is D1 Cathode (band side) connected to the fuse? I see the Anode is connected to Ground. If it is connected to the fuse, then it can be just plain diode to protect reverse power supply polarity connection, or it can be TVS Diode in case the feeding voltage is too high.
              Last edited by budm; 05-23-2013, 10:25 AM.
              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


                #8
                Re: Philips 40PFL3505D/F7 Question about FET replacment

                smaj14a
                Attached Files

                Comment


                  #9
                  Re: Philips 40PFL3505D/F7 Question about FET replacment

                  Thanks guys found the diode..

                  As far as the 3A fuse goes, what does the voltage rating need to be, just anything over 12V? And Fast or Slow blow?

                  Comment


                    #10
                    Re: Philips 40PFL3505D/F7 Question about FET replacment

                    Use type "T", time delay.
                    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                    Comment


                      #11
                      Re: Philips 40PFL3505D/F7 Question about FET replacment

                      twice as much or more, it has to do with arc over the open junction when the fuse blow, it must not be able to allow the arc to jump over the open fuse element. I use PICO II fuse rated at 125V.
                      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


                        #12
                        Re: Philips 40PFL3505D/F7 Question about FET replacment

                        It's 12V DC... is there much chance of the arc not extinguishing if the fuse is rated to at least 12V DC?
                        Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                        For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                        Comment


                          #13
                          Re: Philips 40PFL3505D/F7 Question about FET replacment

                          I never use or find any fuse rated at 12V, the lowest is the 32V for automotive fuse. I always spec in twice as much if it is available.

                          "Are ac and DC Fuses the Same?
                          Direct currents are very difficult to stop or interrupt
                          when compared to alternating currents. Alternatingcurrent sources reverse the flow of current 120 times a
                          second (in some locations 100 times a second on 50
                          Hz systems). Each time the current reverses, it goes to
                          zero in magnitude. A zero current is very easy for a
                          melting fuse to stop or interrupt—it is already stopped,
                          and there is no force trying to sustain an arc across the
                          fuse element.
                          DC currents, as the name implies, are currents that
                          travel in one direction only. They do not reverse. Fuses
                          bear the entire burden (with no help from the current) of
                          acting to stop these currents. The internal elements of a
                          fuse must react to an overcurrent condition (usually by
                          melting) and as they react, they must do so with
                          enough capability to interrupt the current from flowing
                          while extinguishing any arc that might form. DC fuses
                          are relatively sophisticated devices that have many
                          different internal elements that must work together. The
                          complexity of DC fuses makes them cost more than ac
                          fuses that may contain only a single, meltable link."
                          Attached Files
                          Last edited by budm; 05-23-2013, 06:48 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


                            #14
                            Re: Philips 40PFL3505D/F7 Question about FET replacment

                            So I ordered the T-Con parts

                            1 3 SMAJ14ALFCT-ND DIODE TVS 14V 400W UNI 5% SMA
                            2 3 F1659CT-ND FUSE 125V TIME-LAG 3A SMD

                            In the mean time I put a 5A 72v fuse in the T-Con I had from a bad inverter board to test it with the shorted diode removed and the TV is finally working!!

                            Thanks everyone for helping!
                            Attached Files
                            Last edited by kevinm34232; 05-23-2013, 08:00 PM.

                            Comment


                              #15
                              Re: Philips 40PFL3505D/F7 Question about FET replacment

                              Glad to hear nothing else was damaged, so it is 14V TVS 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


                                #16
                                Re: Philips 40PFL3505D/F7 Question about FET replacment

                                I put the old PS board in and TV clicks on with no backlight, then clicks off. Something else is still wrong with that one unfortunately.

                                Comment


                                  #17
                                  Re: Philips 40PFL3505D/F7 Question about FET replacment

                                  Hi could use some help here on the inverter section, I have all other voltages but the 24v to inverters. Was looking for the 345V, I tested cathode of D1607 and D1609 and have 114V, is that where I should have 345V?

                                  I also have 17V to VCC of IC1401.
                                  Attached Files

                                  Comment


                                    #18
                                    Re: Philips 40PFL3505D/F7 Question about FET replacment

                                    114V AC, or DC?
                                    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                                    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                                    Comment


                                      #19
                                      Re: Philips 40PFL3505D/F7 Question about FET replacment

                                      DC, I found I do have 345V dc on cathode of D1606 though

                                      Comment


                                        #20
                                        Re: Philips 40PFL3505D/F7 Question about FET replacment

                                        I also have the 345V to the center pin of Q1701 but nothing on the other pins
                                        Attached Files

                                        Comment

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