Phillips Magnavox 42MF438B/F7 does not power up

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  • mike123333
    Senior Member
    • Oct 2011
    • 196
    • USA

    #1

    Phillips Magnavox 42MF438B/F7 does not power up

    I recently aquired a Phillips Magnavox 42MF438B/F7 that presently does not power up. When I received the LCD TV it would blow the main board fuse. It appeared that the bridge rectifier and a mofset were blown. I managed to repalce both components and the fuse does not blow anymore. The only voltage I have going to the main board is the 3.3v. I do not have the 12v and 24v. the front LED does not light up no fucntion what so ever. I have been combing the board for any other compents that might have blown but nothign jumps out at me. All other fuses on the board are good.

    Any input would be greatly appreciated. The chasis number is LC8.14LA

    I attached photos of the PS board.
    Attached Files
  • retiredcaps
    Badcaps Legend
    • Apr 2010
    • 9271

    #2
    Re: Phillips Magnavox 42MF438B/F7 does not power up

    Originally posted by mike123333
    The only voltage I have going to the main board is the 3.3v.
    Strange. Normally most electronics use 5V for standby voltage. Is 5V standby present on the power board and the main board?
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    Comment

    • mike123333
      Senior Member
      • Oct 2011
      • 196
      • USA

      #3
      Re: Phillips Magnavox 42MF438B/F7 does not power up

      The PS only has 3.3v, 12v, and 24v...the 3.3v exists without the board going to the attached main board. I believe from there the relay switches and energizes the other components.

      I don't have an esr meter to check the capacitors, they do not appear to have issues physically.

      what is the best way of checking the tranformers and mofsets when energized?

      Comment

      • selldoor
        Slow Learner
        • Dec 2010
        • 7870

        #4
        Re: Phillips Magnavox 42MF438B/F7 does not power up

        Pictures are not really clear enough for trouble shooting
        can you get them a bit sharper - good light is the key.
        Need pics of the main board as well.
        On this board top left in your picture there is a half hidden orange component - is it a fuse? does the board designator begin with an F.

        Please can you also update your profile with Country and Mains Voltage
        Please upload pictures using attachment function when ask for help on the repair
        http://www.badcaps.net/forum/showthread.php?t=39740

        Comment

        • mike123333
          Senior Member
          • Oct 2011
          • 196
          • USA

          #5
          Re: Phillips Magnavox 42MF438B/F7 does not power up

          I will get better photos. I was using my iphone for quick photos. As for the orange component it is a fuse. when measured checks out good.

          Comment

          • mike123333
            Senior Member
            • Oct 2011
            • 196
            • USA

            #6
            Re: Phillips Magnavox 42MF438B/F7 does not power up

            Hopefully these photos will help. Thanks!
            Attached Files

            Comment

            • tom66
              EVs Rule
              • Apr 2011
              • 32560
              • UK

              #7
              Re: Phillips Magnavox 42MF438B/F7 does not power up

              Okay there is a pin marked "Standby" on the PSU. With boards installed in TV and everything connected up what does this read?
              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

              • selldoor
                Slow Learner
                • Dec 2010
                • 7870

                #8
                Re: Phillips Magnavox 42MF438B/F7 does not power up

                Busy day tomorrow so off to bed- have just to say im blown away with that first picture. Dont need to check the fuse its so clear we can see the wire. - fantastic
                Please upload pictures using attachment function when ask for help on the repair
                http://www.badcaps.net/forum/showthread.php?t=39740

                Comment

                • mike123333
                  Senior Member
                  • Oct 2011
                  • 196
                  • USA

                  #9
                  Re: Phillips Magnavox 42MF438B/F7 does not power up

                  with all the components attached to the PS the standby voltage is 0.000V DC.
                  With nothing on the board the voltage measures 2.655V DC

                  Comment

                  • mike123333
                    Senior Member
                    • Oct 2011
                    • 196
                    • USA

                    #10
                    Re: Phillips Magnavox 42MF438B/F7 does not power up

                    Selldoor - I am not following you...which wire are you referring to??

                    Comment

                    • retiredcaps
                      Badcaps Legend
                      • Apr 2010
                      • 9271

                      #11
                      Re: Phillips Magnavox 42MF438B/F7 does not power up

                      Originally posted by mike123333
                      Selldoor - I am not following you...which wire are you referring to??
                      He is just complementing you on the pictures. They are so clear and focused you can see the fuse filament wire intact through the glass casing.

                      The regulars, only a handful of volunteers, see about 90% of the pictures posted here either with one of the following characteristics

                      i) out of focus
                      ii) posted inline (which irritates me)
                      iii) posted offsite (which also irritates me)
                      iv) poor composition
                      v) or uses someone's photos

                      Only 10% of the pictures posted are clear enough for our requirements to do remote troubleshooting.
                      --- begin sig file ---

                      If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                      We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                      Please do not post inline and offsite as they slow down the loading of pages.

                      --- end sig file ---

                      Comment

                      • mike123333
                        Senior Member
                        • Oct 2011
                        • 196
                        • USA

                        #12
                        Re: Phillips Magnavox 42MF438B/F7 does not power up

                        Ayone have any suggestions as to what I check? still troubleshooting but coming up with nothing.

                        Comment

                        • tom66
                          EVs Rule
                          • Apr 2011
                          • 32560
                          • UK

                          #13
                          Re: Phillips Magnavox 42MF438B/F7 does not power up

                          So when you unplug the main board power connector, STBY pin rises to ~2.6V, do outputs 12V, 24V etc appear? When plugged in, are they still dead?
                          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

                          • mike123333
                            Senior Member
                            • Oct 2011
                            • 196
                            • USA

                            #14
                            Re: Phillips Magnavox 42MF438B/F7 does not power up

                            the STBY voltage goes to 2.6v but there is no 12v or 24v. I did find a dead LED on the main board but I don't think this would affect anything?

                            Comment

                            • tom66
                              EVs Rule
                              • Apr 2011
                              • 32560
                              • UK

                              #15
                              Re: Phillips Magnavox 42MF438B/F7 does not power up

                              Dead LED? What do you mean?

                              I think your problem is with the P/S. I will try and find schematics though for LG PSUs they are usually made of unobtanium.
                              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

                              • mike123333
                                Senior Member
                                • Oct 2011
                                • 196
                                • USA

                                #16
                                Re: Phillips Magnavox 42MF438B/F7 does not power up

                                dead meaning when I set my meter in diode mode the light will not emit. I have tested others on the board that work fine.. I don't think it would casue any issues.

                                When I aquired the TV my freind mentioned that the TV shutdown in a power outage. When I got the tv there was a ground trace on the bottom of the PS that blew I rewired that and then noticed the rectifier and mofset having the issues. Since then those 2 components were replace..I just wanted to add those comments as to the background of the issues that the tv went through.

                                Comment

                                • tom66
                                  EVs Rule
                                  • Apr 2011
                                  • 32560
                                  • UK

                                  #17
                                  Re: Phillips Magnavox 42MF438B/F7 does not power up

                                  Some meters can't provide enough voltage drop to light certain high brightness green, blue or white LEDs.

                                  I would advise you start checking all the diodes on the output side of the power supply.
                                  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

                                  • mike123333
                                    Senior Member
                                    • Oct 2011
                                    • 196
                                    • USA

                                    #18
                                    Re: Phillips Magnavox 42MF438B/F7 does not power up

                                    I am using a fluke 179 which I would assume to be a good meter. I checked them before but will check them again. What about electrolytic caps, i do not have an esr meter to check. I am wondering whether maybe they are posing any issues even though they physically look good. I may remove them and test one at a time with capacitance.

                                    Comment

                                    • selldoor
                                      Slow Learner
                                      • Dec 2010
                                      • 7870

                                      #19
                                      Re: Phillips Magnavox 42MF438B/F7 does not power up

                                      Hi if you start checking caps start with the small ones on the primary side may be 50v68uf - one of them will be a start up cap. Just to check, you did test both orange fuses?
                                      Please upload pictures using attachment function when ask for help on the repair
                                      http://www.badcaps.net/forum/showthread.php?t=39740

                                      Comment

                                      • mike123333
                                        Senior Member
                                        • Oct 2011
                                        • 196
                                        • USA

                                        #20
                                        Re: Phillips Magnavox 42MF438B/F7 does not power up

                                        yes I did check the orange fuses they were tied together. They checked out good.

                                        Comment

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